The basic knowledge content about strain gauges you provided is very comprehensive and clear, covering key information such as the core concepts, principles, types, application scenarios and selection considerations of strain gauges. Based on your content, the following further supplementary explanations are made from the perspective of knowledge sorting and understanding deepening to help master the relevant knowledge more systematically:

Sorting out the core knowledge system of strain gauges

1. Definition and core principle of strain gauge

• Definition: A strain gauge is a sensor that converts the mechanical strain (deformation) on the surface of an object into measurable resistance changes, and it is a "bridge" for stress and strain measurement.
• Core principle - Resistance strain effect:
  When a conductor (or semiconductor) is deformed (elongated or shortened) under the action of an external force, its resistance value will change accordingly. Specifically:
• Length change: When the object is stretched, the length of the strain gauge increases, and the resistance increases; when compressed, the length shortens, and the resistance decreases.
• Cross - sectional area change: When stretched, the cross - sectional area decreases, and the resistance increases; when compressed, the cross - sectional area increases, and the resistance decreases.
• Gauge Factor (GF): It is a key parameter to quantify this effect. The calculation formula is GF = (ΔR/R) / ε, where ΔR/R is the relative change rate of resistance, and ε is the strain value (unit: microstrain, 1με = 10⁻⁶). By measuring ΔR/R and combining with GF, the strain ε can be calculated.

2. Comparison of characteristics of common strain gauge types

Different types of strain gauges have different applicable scenarios due to differences in materials and structures. The specific comparison is as follows:

Type	Material	Characteristics	Applicable scenarios
Foil strain gauge	Metal foil (such as copper - nickel alloy)	It is thin (several microns), has high strain transfer efficiency, good heat dissipation and strong consistency.	Conventional environment (room temperature, curved/irregular surface), high - precision measurement
Wire - wound strain gauge	Metal wire (such as constantan wire)	It can withstand high temperatures (up to several hundred degrees), has strong fatigue resistance, but the strain transfer is slightly poor.	High temperature, high strain (such as engine components)
Semiconductor strain gauge	Semiconductor materials (such as silicon)	It has extremely high sensitivity (GF is 50 - 200, which is dozens of times that of metals), but has poor temperature stability and is susceptible to interference.	Ultra - high precision measurement (such as precision instruments, micro - strain detection)
Fiber optic strain gauge	Optical fiber (using light interference/scattering)	It is resistant to electromagnetic interference, corrosion, suitable for long - distance transmission, and does not require a power supply.	Harsh environments (strong electromagnetic, chemical corrosion, high pressure), long - distance monitoring (such as bridges, oil and gas pipelines)

3. Core value in application fields

The essence of a strain gauge is to "convert the stress that cannot be directly observed into measurable electrical signals", so it is indispensable in scenarios where it is necessary to master the stress state of an object:

• Structural health monitoring: Real - time monitoring of strain changes in bridges, high - rise buildings, aircraft wings, etc., to early warn of structural damage (such as cracks, deformation).
• Mechanical design optimization: By measuring the strain distribution of mechanical parts (such as gears, bearings), verify the rationality of the design and reduce the risk of material waste or structural failure.
• Material performance testing: In material tensile/compression experiments, accurately measure strain to calculate key mechanical parameters such as elastic modulus and Poisson's ratio.
• Special fields: In biomedicine, measure bone stress or prosthetic adaptability; in the automotive industry, test the strain limit of the frame during a collision, etc.

4. Key considerations for selecting strain gauges

When selecting a strain gauge, it is necessary to combine the characteristics of the object to be measured and environmental conditions. The core factors include:

• Thermal matching: The thermal expansion coefficients of the strain gauge and the material to be measured should be close, otherwise temperature changes will lead to "false strain" (resistance changes not caused by stress). For example, when measuring aluminum alloys, copper - nickel alloy foil strain gauges (with similar thermal expansion coefficients) should be selected.
• Surface adaptability: Smooth surfaces (such as metals) can be directly pasted; rough surfaces (such as concrete) need to be polished; flexible materials (such as plastics) need to select foil strain gauges with good flexibility.
• Strain range: Brittle materials (such as glass) have a small strain range (usually < 1%), so high - sensitivity and small - range strain gauges should be selected; plastic materials (such as aluminum) have a large strain range, so wire - wound or foil strain gauges with good fatigue resistance should be selected.
• Environmental tolerance: Wire - wound strain gauges are selected for high - temperature environments, sealed optical fiber or metal strain gauges are selected for humid/corrosive environments, and optical fiber strain gauges are selected for strong electromagnetic environments.

Summary

Strain gauge is a basic tool for stress and strain measurement, and its core is to realize the conversion of "deformation - resistance" by using the resistance strain effect of materials. Understanding the characteristics and selection principles of different types of strain gauges is the key to ensuring the accuracy of measurement. Whether in industrial production, engineering monitoring or scientific research experiments, strain gauges are helping people "see" the effect of force and providing data support for safety and efficiency.