Strain gauge
A strain gauge is a device designed to measure physical force, particularly stress and strain in materials. Commonly utilized in mechanical engineering, strain gauges help assess how much stress machinery produces, making them vital in various applications, including aircraft component testing and structural analysis. Typically measuring less than an inch across, strain gauges can be made from thin wire or other materials, with bonded gauges being glued to the test specimens to capture precise measurements.
The most prevalent type, electrical resistance strain gauges, operate on the principle that stretching a wire increases its electrical resistance, while compressing it decreases resistance. Other types include mechanical, hydraulic, optical, and piezoelectric strain gauges, each suited to specific applications and materials. Strain gauges play a crucial role in engineering, aiding in the design and testing of bridges and monitoring structural integrity in landmarks like Mount Rushmore. They are also employed in medical technologies, such as robotic surgery and pressure measurement devices. Overall, strain gauges are essential tools for ensuring safety and functionality across a wide range of fields.
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Strain gauge
A strain gauge (sometimes gage) is a device used to measure physical force. Strain gauges are often used in mechanical engineering research and development to measure how much stress a machine produces. Most are no more than an inch across. Strain gauges are used in aircraft component testing and other manufacturing applications. The majority use very thin wire, though other types exist. A bonded gauge is a strain gauge glued to a test specimen. The gauge itself can be of use only when the stresses applied to it are within its elastic limits and do not permanently alter the gauge's components.
Overview
Stress is the internal resistance (counterforce) of a material to the distorting effects of an external force or load. Strain is the intensity or degree of distortion. Strain is the change in length produced by the force divided by the original length of the material.
Conductive metal that is not being stretched or compressed has a standard electrical resistance from end to end. Stretching it—making it longer and thinner—increases electrical resistance. Compressing it—making it shorter and thicker—decreases electrical resistance.
An electrical resistance strain gauge is the most common type. It uses a long length of thin electrical wire, which is looped back and forth and mounted to a material or substrate. When force is applied to the substrate, both the substrate and the mounted wire stretch. This affects the electrical resistance in the wire. A constant known voltage runs through the gauge and is measured. The change indicates the amount of strain.
The four other main types of strain gauges are mechanical, hydraulic, optical, and piezoelectric. A mechanical strain gauge may be used to measure subsidence. One version, often called a crack monitor, comprises two clear plastic layers with rules printed on them. By noting the difference in the rules, an individual can see how quickly a crack is moving.
A hydraulic strain gauge uses leverage to amplify the strain, so even a small movement can be detected. These often use large and small syringes, which work like hydraulic pistons. The smaller syringe magnifies the movement.
An optical strain gauge measures strain on glass, plastics, and other fragile materials. It uses polarized light shined at an angle and measures how much light is reflected and transmitted. This changes according to the strain on the material.
Piezoelectric strain gauges use quartz crystals and ceramics. These materials generate electrical voltages between their opposite faces, a phenomenon called piezoelectricity. The voltage can be measured to calculate the strain. These are the most sensitive and reliable strain gauges.
Engineers must account for various factors, such as temperature, that might affect the wire and substrate in measurements. Multiple strain gauges are typically used to ensure accuracy.
Strain gauges have many applications. They are used to test aircraft in wind tunnels. Bridge designers use them when considering the stresses and strains of weather and traffic on structures. Strain gauges in cracks on Mount Rushmore allow workers to monitor the rock structure from a safe distance rather than from harnesses. When a crack grows, workers are able to pinpoint the problem and target the area that needs repair. Strain gauges are also used in medicine—for example, in robotic surgery devices, in medical scales, and to measure medical pump pressure and flow.
Bibliography
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