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Strain Gauges: How they Work, Applications, and Types

Strain gauges are devices that are commonly used by engineers to measure the effect of external forces on an object. They measure strain directly, which can be used to indirectly determine stress, torque, pressure, deflection, and many other measurements.

In this post I’ll provide an overview on what strain gauges are and how they work. Then I’ll dive a bit deeper into the different types of strain gauges, provide some example applications, and then go through a detailed case study of one application where I work. If interested in buying a strain gauge to use in your project, I’ll also provide a few places to buy them.

What is a Strain Gauge and How Do They Work?

Types of strain gauges, where to buy strain gauges, strain gauge applications, strain gauge case study.

Strain is a dimensionless measurement that is a ratio of the change in length to the original length of an object. Therefore, a positive strain is the result of stretching a material and negative strain is the result of compression. Stress is a measurement of the force applied divided by the initial cross-sectional area of an object, or the internal resisting capacity of an object.

Figure 1. Left: Composition of a strain gauge ( source ) Right: Example of a strain gauge ( source )

Each strain gauge is composed of a metal foil insulated by a flexible substrate, as shown in the figure above. The two leads pass a current through the gauge, and as the surface of the object being measured stretches or contracts, the change in resistance is measured. This change in resistance is proportional to the change in length on the surface of the object being tested, as shown in the equation below. Strain gauges work by measuring the change in electrical resistance across a thin conductive foil. The gauge factor (or “gage factor”) is the sensitivity of the strain gauge (usually 2). It converts the change in resistance to the change in length.

Equation 1: Gauge factor equation ( source ).

Figure 2. Compression and tension as experienced on a strain gauge ( source ).

As a strain gauge experiences bending, stretching, or twisting, the change in resistance across the metal foil is measured by a Wheatstone bridge. The change in resistance that is measured is proportional to the strain experienced by the object. A user can determine the stress experienced by an object using Hooke’s law (equation shown below) by knowing the material’s modulus of elasticity.

Equation 2: Hooke’s law equation.

While there are many types of strain gauges--for different applications and the degree of freedom to be measured, all of them use a Wheatstone bridge to calculate the change in resistance.

Quarter Bridge Strain Gauge

If you are measuring a single axis, a quarter bridge strain gauge is used, as shown in the figure below. The quarter bridge refers to that fact that only one of the four resistors is variable (Rx) and the other three resistors are fixed. The circuit determines the value of the variable resistor so that the circuit is balanced and no current passes between points B and C.

Figure 3. Wheatstone quarter bridge diagram ( image source: copyright DEWESoft from their PRO Training Series ).

Strain Gauge Rosettes

Some strain gauges called strain gauge rosettes use additional sensors to provide strain measurements in multiple directions. The rosettes are used to determine the complete strain state of an object at the surface. The complete strain state is composed of normal, shear, and principal strains. A biaxial rosette uses two sensors and the strain gauges are mounted perpendicular to each other. For a triaxial rosette, three degrees of measurement are necessary. These gauges are mounted at 0°-45°-90° or 0°-60°-120° relative to each other, depending on the measurements required. Below are some common configurations for strain gauge rosettes (you can see the original 

Figure 4. Strain gauge rosette examples ( image source: copyright DEWESoft from their PRO Training Series ).

Piezoresistor

When measuring strain that is on a small scale, a piezoresistor is often a better measurement tool. These measurements are often so small that they are expressed in micro strain (µε or ε x 10-6). When these sensors are used, the sensitivity changes so the gauge factor is often higher than a typical foil strain gauge. While these sensors record smaller changes in length, they are also more susceptible to temperature changes and are more likely to break than foil gauges.

If you are interested in using a strain gauge for your application, there are a variety of places to get them, here are just a few we use typically use:

Now with strain gauges you will also need very specific instrumentation to power and condition the signal output of a strain gauge. Here are a few options from HBM and more from Omega . We know many enDAQ customers are also interested in adding strain gauge measurement capabilities to our devices to go along with the accelerometers and other sensors and we plan to develop such a solution within the next couple of years (see more on our roadmap )!

The fields of civil engineering and geotechnical monitoring regularly use strain gauges to detect failures in structures like bridges, buildings, and much more. These structures require constant monitoring because any significant deformation could lead to injuries or death. These gauges are commonly used because they have high precision, function well at long distances from the test object, and require minimal effort to set up and maintain over long periods of time.

Testing in the field is frequently quite different from laboratory testing under ideal conditions. One of the reasons strain gauges are highly valued is the fact that they can be used in harsh environments, yielding repeatable results with high precision. When an engineer tests objects with irregular shapes in harsh environments with difficult-to-access configurations, a specialized device like a strain gauge is often needed. For example, aerospace applications use millions of strain gauges to verify results from CAD (Computer Aided Design) and FEA (Finite Element Analysis) simulations. These tests are often conducted in dynamic conditions to display an accurate representation of how different forces affect aircraft.

Figure 5.  Left: Minneapolis steel truss bridge in 2006. Right: Underside of the bridge. ( Source )

Strain gauges are also frequently used for static testing. Some bridges are set up to use wireless telemetry, which transfers the testing results via Ethernet. But other bridges primarily undergo visual inspection or penetrant testing to detect surface defects. While cost-efficient, these methods are without constant inspection, which can lead to catastrophic failures such as with the I-35 Minneapolis steel truss bridge. Beginning in 1990, the bridge was flagged as “structurally deficient” by the federal government, which meant that it had to undergo yearly inspections. However, in the absence of constant monitoring from strain gauges, significant repairs, or replacement, the bridge inevitably collapsed in 2007, killing 13 people. This bridge is just one of roughly 80,000 bridges across the United States that were found, in 2007, to be “structurally deficient.”

Here at Midé ( Note: enDAQ is a division of Midé ), we use strain gauges regularly for project work. Recently, a colleague and I added a strain gauge to our test setup to indirectly measure torque. The project we were working on focused on the design of a deep-sea diving suit. For this experiment, we tested the amount of torque required to rotate a thrust bearing in the arm of the suit by pressurizing the thrust bearing to simulate using it at a depth of up to 530 feet.

Figure 6. Test setup with the strain gauge mounted in between the motor and thrust bearing.

For this test, a strain gauge was mounted to a pedestal in between a motor and a sealed thrust bearing, as shown in the figure above. This assembly was placed inside a high-pressure tank, submerged, and pressurized. The motor was powered by AC current, which made the torque output consistent. The tests conducted measured the resistance of the thrust bearing to axial rotation in both clockwise and counterclockwise directions.

Figure 7. Fully assembled diving suit arm with thrust bearing.

During this test we slowly increased the pressure to determine the resistance of the thrust bearing at different depths. Starting with atmospheric pressure as a base, the pressure was increased to 30, 50, 75, 100, 150, 200, and 250 psig (or pounds per square inch). Each time we increased the pressure, the motor was rotated in both directions for 7-8 seconds. At the highest pressure, a maximum torque was measured by the strain gauge at 35 foot-pounds in the counterclockwise direction (positive torque), as shown in the graph below.

Figure 8. Torque vs. Time testing measurements using a strain gauge.

Strain gauges are profoundly versatile geotechnical tools with very broad applications that help to ensure safety and productivity. They are especially prized for their precision, ease of installation, low cost, long operating life, and the need for very limited maintenance. It is exciting to consider the many future applications of strain gauges in fields such as aerospace, cable bridges, rail monitoring (for railroad systems), and measuring torque and power in a wide range of rotating equipment such as fans, generators, wheels and propellers.

I hope this post helped you to better understand the different types of strain gauges, how they work, and their applications. If you have any questions, don't hesitate to leave a comment or contact us . And if you liked this post, don't forget to subscribe to our enDAQ blog for more on data acquisition, sensors, and analysis. 

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For more on this topic, visit our dedicated Environmental Sensors resource page . There you’ll find more blog posts, case studies, webinars, software, and products focused on your environmental testing and analysis needs.

Gabriel Hollings

Gabe is a Mechanical Engineer at Midé Technology. His background is seals, computer aided design, and materials engineering.

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Strain Gauge | Working , Types , Diagram , Applications

Table of Contents

What is Strain Gauge

A strain gauge is an example of a passive transducer that converts a mechanical displacement into a change of resistance. It is a thin, wafer-like device that can be attached to a variety of materials by a suitable adhesive to measure the applied strain. As the structure is stressed, the resulting strain deforms the strain gauge attached to the structure. It causes an increase in the resistivity of the gauge which produces an electrical signal proportional to the deformation. The strain gauge displacement sensor consists of a structure attached with the strain gauge that elastically deforms when subjected to a displacement shown in Figure 1.32(a).

The change of resistance is very small and it is usually measured using a Wheatstone bridge circuit where a strain gauge is connected into the circuit with a combination of four active gauges for full-bridge, two gauges for half-bridge or a single gauge for the quarter bridge. In half and quarter circuits, the bridge is completed with precision resistors.

Working principle of strain gauge :

Gauge Factor: It is the ration of per unit change in resistance to per unit change in length.

When force is applied to any metallic wire its length increases due to the strain. If L1 is the initial length of the wire and L2 is the final length after application of the force, the strain is given as:

ε =(L2-L1)/L1

Further, as the length of the stretched wire increases, its diameter decreases. so that resistance of the conductor is the direct function of the length. As the length of the conductor increases its resistance increases. This change in resistance of the conductor can be measured easily and calibrated against the applied force. Thus strain gauges can be used to measure force and related parameters like displacement and stress. The input and output relationship of the strain gauges can be expressed by the term gauge factor or gauge gradient, which is defined as the change in resistance R for the given value of applied strain ε.

Requirements of strain gauge material

i. Strain gauge should be small in size with negligible mass. ii. It should be highly sensitive to strain. iii. Strain gauge should have a high value of gauge factor. iv. It should be easily attachable to the specimen. v. It should have a high speed of response with negligible time lag. vi. It should be capable to indicate static, transient, and dynamic strain. vii. It should be capable of remote indication and recording. viii. It should not be sensitive to ambient conditions such as temperature, humidity, vibration, etc. ix. It should be inexpensive, reliable and easily available in various sizes

Types of strain gauges

Based on the principle of working, strain gauges are classified into

• Piezoelectric

Based on mounting, they are classified into

• Bonded strain gauge
• Unbounded strain gauge

Based on construction, they are classified into

• Foil strain gauge
• Semiconductor strain gauge
• Photoelectric Strain gauge
• A wide variety of gauge sizes and grid shapes are available. The metallic strain gauge consists of a very fine wire or metallic foil arranged in a grid pattern. The grid pattern maximizes the amount of metallic wire or foil subject to strain in the parallel direction. The cross-sectional area of the grid is minimized to reduce the effect of shear strain and Poisson’s strain. The grid is bonded to a thin backing called carrier which is attached directly to the test specimen.
• The majority of strain gauges are bonded foil types available in a wide choice of shapes and sizes to suit a variety of applications and typical examples are shown in Figure.

• They consist of a pattern of resistive foil which is mounted on a backing material. They operate on the principle that as the foil is subjected to stress, the resistance of the foil changes in a defined way.
• Bonded foil strain gauges can be as small as 16 mm2 and have strain sensitivity or gauge factor of 2.
• Wire wound gauges are made of round wire of copper-nickel, chrome-nickel, or nickel-iron alloys about 0.0064 cm diameter. The length of the wire is 25 mm or less. The figure shows the example of a wire-wound strain gauges.
• The environmental considerations focus mainly on the temperature of the gauge. Since the resistance is a function of temperature, the strain gauges are susceptible to variations in temperature. Thus, if it is known that the temperature of the gauge will vary due to any influence and the temperature compensation is required to ensure that the force measurement is accurate.

Strain gauge load cell

• A load cell is an electromechanical transducer that converts load acting on it into an analog electrical signal. Load cells provide an accurate measurement of compressive and tensile loads.
• Load cells commonly function by utilizing an internal strain gauge that measures deflection. The amount of strain can be calibrated to determine the force upon the load cell because the modulus of elasticity of a load cell is constant.
• Typically, the force creates the strain in the load cell which is measured by a strain gauge transducer.
• The strain gauge is attached to the object or the strained element where the force is being applied. As the object is stressed due to the applied force, the resulting strain deforms the strain gauge attached to it. It causes an increase in resistivity of the gauge which produces electrical signals proportional to the deformation.
• The measurement of resistivity is the measure of strain which in turn gives the measurement of force or load applied on the object. The change of resistance is generally very small and it is usually measured using a Wheatstone bridge circuit where strain gauges are connected into the circuit.
• The strain gauges are serving as resistors in the circuit. The Wheatstone bridge circuit produces an analog electrical output signal. In a typical strain gauge load cell for measuring force, four strain gauges are attached to the surface of the counterforce and they are electrically connected in a full Wheatstone bridge circuit shown in Figure.

Diaphragm with strain gauge :

1) Strain gauge is a passive type resistance pressure transducer whose electrical resistance changes when it is stretched or compressed. It can be attached to a pressure sensing diaphragm as shown in fig 2) When diaphragm flexes due to the process pressure applied on it, the strain gauge stretches or compresses due to this resistance changes.

3) As soon as the pressure is applied the strain gauge stretches or compresses accordingly and the bridge circuit in fig is unbalanced due to the change in resistance of the strain gauges. 4) Thus a current flows in the galvanometer, Which is measured by the deflection of the galvanometer, this change in output voltage may be calibrated for the pressure change.

Bonded strain gauge :

Working of Bonded Strain Gauges :

• With the help of an adhesive material, the strain gauge is pasted/ bonded on the structure under study. • The structure is subjected to a force (tensile or compressive). Due to the force, the structure will change the dimension. • As the strain gauge is bonded to the structure, the strain gauge will also undergo a change in both in length and cross-section (that is, it strained). • This strain (change in dimension) changes the resistance of the strain gauge which can be measured using a wheat stone bridge. • This change in resistance of the strain gauge becomes a measure of the extent to which the structure is strained and a measure of the applied force when calibrated.

Semiconductor Strain gauge.

• These gauges are produced from silicon and germanium crystals in which a certain amount of special impurities are added to impart certain characteristics.

a) Negative or n-type, whose resistance decreases in response to tensile strain b) Positive or p-type, whose resistance increases in response to tensile strain.

• The breaking stress of material rises as the cross-sectional area decreases.
• The gauge is in the form of a single rectangular filament about 0.05 mm thick and 0.25 mm wide and 1.5 mm to 12 mm in length.
• Advantages: Very high sensitivity in comparison of metal gauges, High gauge factor in the range of 100 to 200. , Low hysteresis.

Applications of Strain Gauge : 

(i) Strain measurement (ii) Residual stress measurement (iii) Vibration measurement (iv) Torque measurement (v) Bending and deflection measurement (vi) Compression and tension measurement

Advantages of Strain Gauge : 

(i) There is no moving part and hence no wear (ii) Strain gauges are very precise (iii) It is small and inexpensive (iv) It has a high-frequency bandwidth.

Disadvantages of Strain Gauge :

(i) It is non-linear (ii) It is very sensitive to temperature. (iii) It needs to be calibrated regularly (iv) Strain gauges have to be applied manually. Putting them in their place consuming and costly. It is one of their biggest disadvantages

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Sachin Thorat

Sachin is a B-TECH graduate in Mechanical Engineering from a reputed Engineering college. Currently, he is working in the sheet metal industry as a designer. Additionally, he has interested in Product Design, Animation, and Project design. He also likes to write articles related to the mechanical engineering field and tries to motivate other mechanical engineering students by his innovative project ideas, design, models and videos.

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What is Strain Gauge : Working and Its Applications

A strain gauge was invented by Edward E. Simmons and Arthur C. Ruge, in 1938. This invention led to the measurement of a significant amount of strain on various structures. A strain gauge is a type of sensor used in a wide variety of applications to measure the strain of an object. It is an essential geotechnical tool that determines strain in a range of structures such as tunnels, underground cavities, buildings, bridges, concretes, masonry dams, embedment in soil/concrete, etc. Here’s everything that a reader can know about the Strain gauge including working principle, characteristics, and applications.

What is a Strain Gauge?

Definition: A strain gauge is one of the imperative devices used in the field of geotechnical engineering to measure strain on diverse structures. By applying an external force, there would be a change in resistance of a strain gauge.

The basic construction of a gauge has an insulating flexible backing to support a metallic foil structure. This metallic coil is glued to a thin backing called a carrier, and the entire setup is fixed to an object using a suitable adhesive. As the object is deformed due to force, pressure, weight, tension, etc., the electrical resistance of foil changes. A Wheatstone bridge measures the change in resistivity, which is related to strain through a quantity known as Gauge Factor.

The small changes in resistance of a gauge are measured using the concept of Wheatstone bridge. The figure below illustrates the general Wheatstone bridge, which has four resistive arms and an excitation voltage, V EX .

The Wheatstone bridge has two parallel voltage divider circuits. R1 and R2 form a one voltage divider circuit, R3 and R4 form second voltage divider circuit. The output voltage VO is given by:

Vo=[R3/(R3+R4 )-R2/(R1+2)]* V EX

If R1/R2 = R4/R3, then the output voltage is zero and the bridge is said to be a balanced bridge.

A small change in resistance leads to a nonzero output voltage. If ‘R4’ is replaced with a strain gauge and any changes in the resistance of strain gauge will unbalance the bridge and produce nonzero voltage.

Gauge Factor of Strain Gauge

The gauge factor GF is given as

GF= (∆R⁄RG )/∈

‘ΔR’ is the change in resistance due to strain

‘RG’ is the resistance of the undeformed gauge

‘ε’ is the strain

The gauge factor of common metallic foils is around 2. The output sensor voltage SV of a Wheatstone bridge is given by,

SV=EV (GF.∈)/4

Where EV is the bridge excitation voltage

Strain Gauge Working

The functioning of a strain gauge entirely depends on the electrical resistivity of an object/conductor. When an object gets stretched within its limits of elasticity and does not break or buckle permanently, it becomes thinner and longer, resulting in high electrical resistance. If an object is compressed and does not deform, but, broadens and shortens, results in decreased electrical resistance. The values obtained after measuring the electrical resistance of a gauge helps to understand the amount of stress-induced.

The excitation voltage is applied at the input terminals of a gauge network, while the output is read at the output terminals. Normally, these are connected to a load and are likely to remain stable for longer periods, sometimes decades. The glue used for gauges depends on the duration of a measurement system – cyanoacrylate glue is suitable for short term measurements and epoxy glue for long term measurements.

Strain Gauge Working Principle

As we know that the resistance is directly dependent on the length and cross-sectional area of a conductor, which is given by R = L/A

‘R’= Resistance

‘L’ = Length

‘A’ = cross-sectional area

Clearly, the length of a conductor is altered with the change in size and shape of a conductor, eventually, altering the cross-sectional area and resistance.

Any normal gauge has a conductive strip that is long and thin, placed in a zig-zag fashion of parallel lines. The purpose of this zig-zag alignment is to elaborate on the small amount of stress that occurs between the parallel lines with much accuracy. Stress is defined as the resisting force of an object.

Strain Gauges Rosettes

Two or more gauges positioned closely in a rosette-like structure to measure the number of components to evaluate precise strain on the surface are known as strain gauge rosettes. The illustration is shown in the figure below.

Strain Gauge Load Cells

These load cells are most commonly found in industrial applications. It is highly precise and economical. Basically, a load cell consists of a metal body on which strain gauges are attached. For the metal body to be sturdy and less elastic, alloy steel, aluminum, or stainless steel are employed to design.

When an external force is applied on a load cell, the load cell is slightly deformed, and if not overloaded, it returns to its original shape.

If the load cell deforms, the gauge changes in shape, causing the change in electrical resistance of gauge, which in turn measures voltage.

There are common types of strain gauge load cells, which include bending beam, pancake, single point shear beam load cell, double-ended shear beam, wire rope clamps, and so on.

Characteristics of Strain Gauges

The important characteristics of strain gauges are:

• These are appropriate for longer periods with certain precautions
• They provide precise values with a change in temperature and other factors
• These are easy to manufacture because of simple components
• They are easy to maintain and has a long operating life
• This is totally encapsulated to protect from damages like handling and installation

Applications of Strain Gauge

The exceptional features enable these gauges to be used in the field of geotechnical engineering to monitor structures like dams, tunnels, etc. constantly and to avoid accidents well in advance. Some of the applications of strain gauges include –

• Rail monitoring
• Cable bridges
• Nuclear power plants

1). What is the sensitivity of strain gauge?

The flow stress differs with respect to the strain rate. Also, the strain rate relies on the grain size of an object or a work material. It is defined as the ratio of the change in the flow stress to the change in the strain.

2). What is the unit of strain?

The strain is a dimensionless quantity. However, the strain rate is the reciprocal of time and the SI unit is reciprocal of seconds (s-1).

3). How do I choose a strain gauge?

This is selected based on the type of applications and other related elements. Such as –

• Based on gauge length and resistance
• Based on labor-saving cost
• Based on material and measurement environment

4). Why Wheatstone bridge is used for strain gauge?

Wheatstone bridge is capable of measuring output voltages in terms of millivolts. For a bonded strain gauge, a change in resistance can be measured when it is connected to an electrical circuit (Wheatstone bridge) that measures the minute change in resistance. As the output voltage on the Wheatstone bridge becomes non-zero, the circuit loses its balance and helps to determine the strain on the object.

5). How do you install strain gauges?

Here are the steps to install strain gauge

Thus, an extensive description of the strain gauge , the principle of working, gauge factor, characteristics, and applications are provided in this article. Besides this, digital image correlation (DIC) is a technique employed nowadays to measure strain. It is used in many industries because of accuracy and as a replacement of conventional types of sensors like accelerometers, string pots, LVDT, and many more. Here is a question for you, what is the main function of strain gauge?

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Strain Gauge

A strain gauge is a versatile and widely used sensing device that measures strain or deformation in various materials. It is a fundamental component in the field of engineering and plays a crucial role in measuring and monitoring mechanical forces and stresses. Strain gauges are utilized in a wide range of applications, including structural analysis, load testing, material testing, and stress analysis.

The basic principle behind a strain gauge is its ability to convert mechanical strain into an electrical signal. The gauge consists of a thin metallic wire that is attached to the surface of the material under observation. When the material is subjected to strain, the gauge undergoes deformation, which alters the electrical resistance of the metallic element. This change in resistance is directly proportional to the applied strain, allowing for accurate measurements. In this article, we will discuss about the strain gauge in detail. So, stay in this article for more information.

What is Strain Gauge?

A strain gauge is a device used to measure the strain or deformation of an object under external forces. It is widely employed in the field of solid mechanics to quantify the amount of stress experienced by a material. The gauge consists of a wire or a foil patterned in a zigzag or grid-like configuration, which undergoes changes in its electrical resistance when subjected to mechanical strain. Strain gauges find extensive applications in various fields, including structural engineering, aerospace, automotive, and materials testing. They are used to monitor and analyze the behavior of structures, determine material properties, assess structural integrity, and optimize designs.

When an external force is applied to an object, it causes the object to deform. This deformation alters the length and cross-sectional area of the strain gauge, leading to a change in its electrical resistance. This change in resistance is directly proportional to the amount of strain experienced by the object. To measure the strain, the strain gauge is typically attached to the surface of the object being tested using adhesive or solder. As the object deforms, the strain gauge undergoes the same deformation, resulting in a change in resistance.

Strain Gauge Working Principle

Strain gauge working principle is based on the concept of electrical resistance variation due to mechanical strain. The strain gauge consists of a fine wire or foil, typically made of a highly conductive material like copper or constantan, which is attached to a flexible backing material. When a mechanical strain is applied to the strain gauge, the wire or foil undergoes deformation, resulting in a change in its length and cross-sectional area. This alteration in dimensions causes a corresponding change in the electrical resistance of the wire or foil.

The change in resistance can be measured using a Wheatstone bridge circuit, which is commonly employed in strain gauge applications. The Wheatstone bridge consists of four resistive arms, with the strain gauge forming one of the arms. The other three arms typically consist of fixed resistors. When the strain gauge experiences a strain, the resistance of the gauge changes, leading to an imbalance in the Wheatstone bridge circuit. This imbalance generates a small electrical output signal, which is proportional to the applied strain.

By measuring the output signal, the magnitude of the strain can be determined. This allows for the analysis of various mechanical properties such as stress, load, and deformation in structural components. Strain gauges find extensive applications in areas like civil engineering, aerospace, automotive, and material testing. We will learn more about its applications in civil engineering in following sections.

Applications of Strain Gauge

The applications of strain gauges in the field of civil engineering are invaluable. Strain gauges are extensively used to measure and monitor the deformations and stresses experienced by various structural components and materials. These devices play a crucial role in ensuring the safety, durability, and efficiency of civil engineering projects.

One significant application of strain gauges is in the field of structural health monitoring. By attaching strain gauges to critical sections of structures such as bridges, dams, and buildings, engineers can accurately measure the strains and stresses these structures endure under normal and extreme conditions.

Strain gauges are also used in experimental studies and material testing. In SOM, researchers often apply strain gauges to test specimens and structural models to study the behavior of materials under different loads and environmental conditions. By measuring the strains in real-time, engineers gain insights into the material properties, stress distributions, and failure mechanisms, aiding in the development of safer and more efficient designs.

Strain gauges also have application in geotechnical engineering. They are employed to monitor the deformations in soil, rock, and underground structures such as tunnels and retaining walls. By measuring the strains caused by ground movements, engineers can assess the stability of slopes, predict potential failures, and implement appropriate measures to prevent disasters.

Advantages and Disadvantages of Strain Gauge

Strain gauges are widely used in civil engineering applications to measure strain or deformation in structural components. They are small devices that detect changes in electrical resistance when subjected to mechanical strain. While strain gauges offer several advantages, they also have certain limitations that need to be considered. So, Let’s understand them properly:

Advantages of Strain Gauge

• High Sensitivity: Strain gauges have excellent sensitivity, allowing for accurate measurement of even minute deformations. This feature is crucial in civil engineering, as it helps detect structural movements or stress concentrations that may affect the integrity of a building or infrastructure.
• Versatility: Strain gauges can be used on various materials such as concrete, steel, or composites, making them versatile for different civil engineering applications. They can be attached to surfaces or embedded within structures, enabling engineers to monitor strain at specific locations of interest.
• Cost-Effective: Strain gauges offer a cost-effective solution for strain measurement compared to other techniques such as extensometers. They are relatively inexpensive and reusable, allowing for multiple measurements at different locations within a structure.
• Real-Time Monitoring: Strain gauges provide real-time data, allowing engineers to monitor structural behavior continuously. This feature is particularly useful during load testing, construction, or seismic events, as it enables prompt identification of any excessive strains or deformations.

Disadvantages of Strain Gauge

• Installation Complexity: The installation of strain gauges can be a time-consuming and intricate process, requiring expertise and precision. Specialized knowledge is necessary to ensure proper attachment, wiring, and calibration of the strain gauges, which can increase the overall project complexity.
• Susceptible to Environmental Factors: Strain gauges are sensitive to environmental conditions such as temperature, humidity, and vibration. These factors can introduce additional strains or interfere with the accuracy of measurements. Proper environmental controls and shielding techniques are necessary to mitigate these influences.
• Limited Measurement Range: Each strain gauge has a specific measurement range, beyond which it may not provide accurate readings. This limitation restricts their application in cases where high strains are expected, such as during dynamic load testing or extreme events like earthquakes.
• Vulnerability to Damage: Strain gauges are delicate and can be easily damaged during construction activities or due to accidental impacts. Protecting them from mechanical damage is crucial to ensure reliable and consistent measurements.

Types of Strain Gauge

In civil engineering, strain gauges are essential instruments used to measure and monitor the strain or deformation of structural components. They play a crucial role in assessing the structural integrity and performance of various civil engineering projects. Strain gauges come in different types, each designed to suit specific applications and measurement requirements. It can be categrized into following types:

• Electrical Resistance Strain Gauges: Electrical resistance strain gauges are the most widely used type in civil engineering applications. They consist of a grid of fine metallic wire or foil bonded to a backing material. When subjected to strain, the wire or foil experiences a change in resistance, which is measured using a Wheatstone bridge circuit. These strain gauges offer high sensitivity, accuracy, and stability, making them suitable for measuring small strains in structures such as bridges, dams, and buildings.
• Vibrating Wire Strain Gauges: Vibrating wire strain gauges utilize the principle of the resonant frequency of a wire to measure strain. They consist of a taut wire stretched between two anchor points. When subjected to strain, the tension in the wire changes, altering its resonant frequency. By measuring the frequency change, the strain can be determined. Vibrating wire strain gauges are particularly useful in geotechnical and structural monitoring applications due to their robustness, long-term stability, and resistance to environmental factors.
• Fiber Optic Strain Gauges: Fiber optic strain gauges utilize optical fibers to measure strain. They operate based on the phenomenon of the strain-induced change in the light transmission characteristics of the fiber. The fiber optic sensor consists of a section of optical fiber embedded or bonded to the structure being monitored. As strain is applied, it alters the light intensity or wavelength propagating through the fiber, which is then detected and analyzed. Fiber optic strain gauges offer several advantages such as high accuracy, immunity to electromagnetic interference, and the ability to multiplex multiple sensors along a single fiber.
• Piezoelectric Strain Gauges: Piezoelectric strain gauges employ the piezoelectric effect to measure strain. They consist of a piezoelectric crystal or ceramic material that generates an electric charge when subjected to mechanical deformation. This charge is proportional to the applied strain and can be measured using specialized equipment. Piezoelectric strain gauges are highly sensitive and capable of measuring dynamic strains in structures such as bridges, tunnels, and pavements. However, they are susceptible to temperature variations and exhibit a limited range of linearity.

What is Strain Gauge Rosette

A strain gauge rosette is an essential tool used in civil engineering to measure strain in various structures and components. It consists of three or more strain gauges arranged in a specific pattern, typically at different angles to each other. These gauges are small devices that change their electrical resistance when subjected to strain or deformation. The purpose of using a rosette configuration is to measure strains in multiple directions, allowing engineers to obtain a complete picture of the strain state in a structure. By placing the strain gauges at different orientations, the rosette can measure strains in the axial and transverse directions, as well as shear strains.

To use a strain gauge rosette, the gauges are carefully bonded to the surface of the structure under investigation. As the structure undergoes deformation or load, the strain gauges experience strain, which causes a change in their electrical resistance. These changes are then measured using a strain indicator, providing valuable information about the strain distribution within the structure.

Civil engineers utilize strain gauge rosettes in a variety of applications. They are commonly used to monitor the behavior of structural elements such as beams, columns, and bridges. By analyzing the strain data, engineers can assess the structural integrity, evaluate the effectiveness of design modifications, and ensure the safety of the structure under different loading conditions.

Frequently Asked Questions on Strain Gauge

What is a strain gauge.

A strain gauge is a sensor used to measure the strain or deformation of an object by detecting changes in its electrical resistance. It consists of a thin metallic wire or foil that is attached to the surface of the object being measured.

What are the applications of strain gauges?

Strain gauges have a wide range of applications across various industries. They are commonly used in engineering and structural analysis to measure stress and strain in materials, such as load cells, pressure sensors, force transducers, and torque sensors. They are also used in experimental stress analysis, aerospace, automotive, and civil engineering applications.

How does a strain gauge work?

A strain gauge operates based on the principle of the piezoresistive effect, where the electrical resistance of certain materials changes when they are subjected to mechanical strain. When the object to which the strain gauge is attached experiences deformation, the strain causes the resistance of the gauge to change. This change in resistance is proportional to the applied strain, allowing for strain measurement.

What are the advantages of using strain gauges?

Strain gauges offer several advantages, including high accuracy, sensitivity, and reliability. They can be easily attached to the surface of various materials, providing a non-intrusive measurement method.

What are the disadvantages of using strain gauges?

One major disadvantage of strain gauges is their sensitivity to temperature changes. The resistance of the gauge can be affected by temperature variations, leading to inaccurate measurements.

What is a strain gauge rosette?

A strain gauge rosette is a configuration of multiple strain gauges that are strategically placed on an object to measure strain in multiple directions. By using a rosette, strain measurements can be taken along different axes, allowing for a more comprehensive understanding of the object’s deformation.

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Strain gauge.

Strain gauges are sophisticated sensory devices used to measure mechanical strain in materials. Their importance lies in their ability to provide accurate and reliable measurements, allowing for a deeper understanding of material behavior and structural integrity.

The historical evolution of strain gauges dates back to the late 19th century when Lord Kelvin developed the concept of electrical resistance. Their evolution has been marked by advancements in technology, leading to the development of various types of strain gauges.

Strain measurements play a crucial role in numerous fields, including engineering, research, and industrial sectors. They provide valuable insights into the behavior of materials under different conditions, aiding in designing and optimizing structures and products.

Strain gauges are designed to detect changes in the length of an object or material when subjected to an external force or load. These changes result in deformations known as strains. By measuring these strains, engineers and researchers can gather essential data about the mechanical properties and performance of materials.

The historical journey of strain gauges is closely tied to the evolution of electrical resistance theory. Lord Kelvin's pioneering work in the late 19th century laid the foundation for understanding how the resistance of a conductor changes when it undergoes mechanical deformation. This concept formed the basis for the development of strain gauges.

Over the years, technological advancements have led to the creation of various types of strain gauges, each catering to specific measurement requirements. These gauges are constructed using thin wires, foils, or semiconductor materials. As the material experiences strain, its electrical resistance changes proportionally, which can be measured and correlated to the applied force or stress.

Strain gauges have become indispensable tools in modern engineering and scientific research. They are extensively used in fields such as aerospace, civil engineering, automotive, and biomechanics. In aerospace applications, strain gauges monitor the structural health of aircraft components, ensuring safety and reliability. Civil engineers employ strain measurements to assess the integrity of bridges, dams, and buildings under various loads and environmental conditions.

The automotive industry relies on strain gauges to evaluate the performance and durability of vehicle components. In biomechanics, these devices aid in studying human movement and the interaction between muscles, bones, and external forces.

Understanding Strain Measurements

• Concept of Mechanical Strain in Materials - Mechanical strain refers to the deformation experienced by a material when subjected to external forces. - It is measured as the fractional change in the material's length, area, or volume.
• Importance of Accurate Strain Measurements - Accurate strain measurements enable engineers and researchers to understand how materials respond to external loads. - This understanding is vital for designing safe and efficient structures, predicting failures, and optimizing performance.
• Different Types of Strain: Tensile, Compressive, Shear, and Bending - Tensile strain occurs when a material is stretched, while compressive strain occurs when it is squeezed. - Shear strain describes the deformation resulting from forces applied parallel to a material's surface. - Bending strain refers to the deformation that occurs when a material is subjected to a combination of tensile and compressive forces.

Basics of Strain Gauge Technology

• Construction and Composition of Strain Gauges - Strain gauges consist of a thin metallic foil or semiconductor material attached to a flexible backing. - The composition is carefully selected to exhibit the desired electrical resistance changes when strained.
• Principle of Piezoresistance: Unveiling the Working Mechanism - The working mechanism of a strain gauge is based on the principle of piezoresistance. - Piezoresistive materials exhibit a change in electrical resistance when subjected to strain.
• Factors Influencing the Performance of Strain Gauges - The performance of strain gauges is influenced by factors such as temperature, humidity, and adhesive compatibility. - Calibration and installation techniques also play a vital role in ensuring accurate and reliable measurements.

Types of Strain Gauges

• Metal Foil Strain Gauges: Most Common and Versatile Type - Metal foil strain gauges are widely used due to their excellent durability, flexibility, and cost-effectiveness. - They are suitable for a broad range of applications, including automotive, aerospace, and material testing.
• Semiconductor Strain Gauges: Enhancing Sensitivity and Precision - Semiconductor strain gauges offer higher levels of sensitivity and precision compared to metal foil gauges. - They are commonly used in applications that require extremely accurate measurements, such as atomic force microscopy.
• Thin-Film Strain Gauges: High Stability and Resistance to Environmental Effects - Thin-film strain gauges exhibit enhanced stability and resistance to environmental influences, such as temperature variations and humidity. - They are often used in applications where long-term measurements or exposure to extreme conditions are required.
• Advanced Optical Strain Gauges: Utilizing Optical Interferometry - Advanced optical strain gauges employ optical interferometry principles to measure strain. - They offer exceptional precision and are commonly used in research and specialized applications.

Installation and Mounting Techniques

• Proper Pre-Installation Considerations - Before installing strain gauges, it is imperative to consider factors such as material properties, surface conditions, and strain gauge orientation. - Proper planning and preparation ensure accurate and reliable measurements.
• Surface Preparation Methods - The surface preparation of the material is vital for achieving optimal performance from strain gauges. - It typically involves cleaning, roughening, and applying a suitable primer or adhesive to maximize adhesion.
• Selecting Suitable Adhesives and Protective Coatings - The choice of adhesive and protective coating depends on the material being tested and the environmental conditions involved. - The selected materials should ensure proper bonding, electrical insulation, and protection against moisture and contaminants.
• Mounting Techniques for Different Applications: Static vs. Dynamic Measurements - Static measurements require strain gauges to be securely attached to the material. - Dynamic measurements involve mounting techniques that minimize the effects of vibration and strain rate variations.

Calibration and Measurement Accuracy

• Importance of Calibration in Ensuring Accuracy - Calibration is essential for achieving accurate and reliable strain measurements. - It involves establishing a known relationship between the electrical output of the strain gauge and the applied strain.
• Calibration Techniques for Strain Gauges: Dummy and Shunt Calibration - Dummy calibration involves applying a known strain to the structure to validate the measurements obtained. - Shunt calibration involves the application of a known resistance in parallel with the strain gauge to verify its accuracy.
• Evaluating Measurement Uncertainty and Error Sources - Measurement uncertainty should be carefully evaluated to determine the level of confidence in the obtained strain measurements. - Sources of error, such as temperature variations, electrical noise , and strain gauge aging, should be identified and minimized.

Strain Gauges in Structural Health Monitoring

• Assessing Structural Integrity and Preventing Failures - Strain gauges play a critical role in the monitoring and assessment of structural integrity. - They help identify potential weaknesses, predict failures, and prevent catastrophic incidents.
• Real-Time Monitoring of Bridges, Dams, and Buildings - Strain gauges installed on bridges, dams, and buildings provide real-time data on structural behavior, ensuring their safe operation. - Continuous monitoring allows for early detection of any abnormalities, enabling timely maintenance and repairs.
• Integration of Strain Gauges with Wireless Sensor Networks - Strain gauges can be integrated into wireless sensor networks, providing easy access to data and simplifying monitoring systems. - This integration enhances data collection, analysis, and decision-making processes.

Industrial Applications of Strain Gauges

• Automotive Industry: Enhancing Vehicle Safety and Performance - Strain gauges are extensively used in the automotive industry to measure stresses and strains in components and structures. - They aid in improving vehicle safety, optimizing performance, and ensuring compliance with safety standards.
• Aerospace Industry: Ensuring Structural Integrity of Aircraft - Strain gauges are crucial in the aerospace industry for monitoring the structural health of aircraft. - They provide vital information on stress distribution, fatigue, and load-bearing capacities, ensuring safe and reliable flight operations.
• Energy Sector: Monitoring Stress in Wind Turbines and Power Plants - In the energy sector, strain gauges are employed to monitor stress levels in critical infrastructure such as wind turbines and power plants. - Accurate strain measurements help optimize maintenance schedules, prevent downtime, and ensure the long-term reliability of these assets.

Strain Gauges in Material Testing and Research

• Measuring Material Properties and Behavior - Strain gauges enable researchers to measure and analyze the behavior of materials under various conditions. - This information is valuable for understanding material properties, exploring new applications, and enhancing product development.
• Investigating the Strength and Durability of Various Structures - Strain gauges play a crucial role in investigating the strength, durability, and failure mechanisms of structures. - They help engineers design resilient structures and ensure they meet safety requirements.
• Applications in Biomechanics and Medical Research - Strain gauges find applications in biomechanics and medical research, aiding in the study of human movement and physiological response. - They contribute to the development of medical devices, orthopedics, and rehabilitation techniques.

Strain Gauges in Robotics and Automation

• Optimizing Efficiency and Performance in Robotics - Strain gauges are employed in robotics to monitor the forces and strains experienced by robotic components. - This information enables optimization of performance, control, and efficiency in robotics applications.
• Implementing Feedback Control Systems - Strain gauges play a pivotal role in feedback control systems, enabling real-time adjustments and corrections. - They contribute to precision, stability, and safety in various industrial and automation processes.
• Enhancing Precision in Industrial Automation - Strain gauges are integrated into industrial automation systems to measure and control crucial parameters. - Their ability to provide precise strain measurements enables accurate process control and enhances overall system performance.

Emerging Trends and Future Prospects

• Miniaturization of Strain Gauges for Microscopic Applications - The miniaturization of strain gauges opens up possibilities for microscopic applications in fields like microelectronics and nanoengineering. - These highly sensitive sensors contribute to advancements in miniaturized devices and systems.
• Integration of Strain Gauges with IoT and Data Analytics - Strain gauges integrated with the Internet of Things (IoT) facilitates the collection and analysis of strain data on a large scale. - This integration enables proactive maintenance decisions, predictive analytics, and optimization of processes.
• Advancements in Wireless Strain Gauge Technology - Wireless strain gauge technology continues to advance, allowing for more reliable and efficient data transmission without physical connections. - This trend contributes to the development of wireless monitoring systems and expands the possibilities for remote and distributed applications.

Challenges and Limitations of Strain Gauges

• Sensitivity to Temperature Variations - Strain gauges are sensitive to temperature changes, which can introduce inaccuracies in the measurements. - Proper temperature compensation techniques are necessary for maintaining measurement accuracy.
• Strain Gauge Fatigue and Lifespan Considerations - Strain gauges experience cyclic loading, leading to fatigue and reduced lifespan. - Monitoring fatigue and implementing appropriate maintenance practices is crucial for reliable and continuous operation.
• Issues Related to Humidity and Environmental Influences - Humidity and environmental factors such as moisture and contaminants can affect strain gauge performance. - Proper sealing and protection measures should be implemented to mitigate these influences.

Benefits and Advantages of Strain Gauges

• Non-Disruptive Testing and Monitoring in Real Time - Strain gauges offer non-disruptive testing and monitoring capabilities, allowing measurements to be taken without disturbing the material or structure under investigation. - Real-time data acquisition ensures prompt responses to changes and deviations.
• High Precision and Accuracy in Strain Measurement - Strain gauges provide highly precise and accurate strain measurements, enabling engineers and researchers to make informed decisions and predictions. - The reliability of the measurements contributes to efficient design, optimization, and maintenance processes.
• Cost-Effectiveness and Versatility in Various Applications - Strain gauges offer a cost-effective solution for a wide range of applications. - Their versatility allows them to be used in different industries, addressing diverse measurement needs.

Summary and Conclusion

In conclusion, strain gauges play a vital role in measuring mechanical strain and understanding material behavior. They have evolved over time, offering a variety of types tailored for specific applications. Proper installation, calibration, and measurement techniques are essential to ensure accurate and reliable results. Strain gauges find applications in industries such as automotive, aerospace, energy, and research. They enable structural health monitoring, material testing, and advancements in robotics and automation. Emerging technologies, such as miniaturization and wireless integration, promise exciting prospects for strain gauge technology. Despite challenges and limitations, strain gauges provide significant benefits, including non-disruptive testing, high precision, and versatility, making them indispensable in various fields.

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