Abstract

In mechanical engineering research and development, strain gauges are commonly used to calculate the stresses produced by machinery. Aircraft component checking is one area of use, tiny strain gauge strips taped to structural parts, linkages, and every other vital component of the airframe for stress analysis. A strain gauge is a mechanism used on an item to measure strain. The calculation of strain gauges plays an important role in many manufacturing industries. The degree of strain occurring in various buildings, from biomechanics to civil engineering, can be described by suitable measuring systems. Life period and hazard of particular construction can be determined depending on strain.  The description, configuration, interfacing circuit, use or applications of strain gauges in strain measurements are seen in this article.

1.    Introduction

Definition

A strain gauge is often referred to as a sensor whose resistance changes with the force applied; it transforms force, friction, friction, weight, etc., into an observable difference in electrical resistance. Stress and pressure are the consequence if external forces are applied to a stationary object. Stress is defined as the internal resisting forces of the object, and strain is defined as the occurrence of displacement and deformation.

Strain gauges measurements play an important role in many industrial sec-

tors. Appropriate  measurements systems can define the strain level occurring

in  different  construction  from  biomechanics  to  civil  engineering.  Based  on

strain, life time and threat of specific construction can be calculated. 

This article shows application of strain gauges in strain measurements 

for charge air cooler during thermal cycle test.

Strain gauges measurements play an important role in many industrial sec-

tors. Appropriate  measurements systems can define the strain level occurring

in  different  construction  from  biomechanics  to  civil  engineering.  Based  on

strain, life time and threat of specific construction can be calculated. 

This article shows application of strain gauges in strain measurements 

for charge air cooler during thermal cycle test.

Structure

On the electrical insulator of the thin resin, the strain gauge has metal foil, and gauge leads attached, as seen in Fig. 1 from below.

Fig. 1 Structure of strain gauge

Source: https://www.kyowa-ei.com/eng/technical/strain_gages/principles.html

The strain gauge is bonded with a dedicated adhesive to the measuring object. Strain that occurs on the measuring site is transferred via adhesive and the resin base to the strain sensing element. The strain gauge and adhesive should be consistent with the measuring medium and working conditions such as temperature, etc for precise calculation.

Interfacing Circuit

The standard resistance of the strain gauge ranges from 30 Ω to 3 kΩ. Given the limitations imposed by the elastic limits of the gauge material and of the test specimen, this resistance can change only a fraction of a percent for the entire force range of the gauge. The measurement specimen and/or the gauge conductors themselves will be forever deformed by forces great enough to cause larger resistance changes, thereby ruining the gauge as a measuring system. Therefore we must calculate incredibly minor changes in resistance with high precision in order to use the strain gauge as a practical method. A bridge measuring circuit calls for such demanding accuracy. A strain gauge bridge circuit shows measured strain by the degree of imbalance, with the exception of the Wheatstone bridge that uses a null-balance detector and a human operator to maintain a state of balance A precision voltmeter in the middle of the bridge is used to precisely calculate this imbalance.

Use of Strain Gauge

– In area of improvement of mechanical engineering.

– To calculate the tension that machinery produces.

– In the field of aircraft part research, such as connections, structural damage, etc.

2.    Literature Review:

The strain gauge is a thin metal strip designed to calculate mechanical load by adjusting resistance when strained (tensile or compressed beyond its elastic limit).

Strain gauge tension effects are usually determined in a bridge circuit, to allow reliable calculation of minor resistance changes, and to adjust for temperature differences in resistance. In the field of geotechnical control, strain gauges are commonly used to keep a steady eye on bridges, dams, tunnels, and buildings so that mishaps can be avoided on time. Strain gauges are attached to longitudinal load-bearing elements to calculate tension along load paths for wing deflection or aeroplane deformation[1]. The strain gauges are connected further into circuits of the Wheatstone Bridge, and their implementation areas include on-board signal conditioning systems, excitation power supplies, and the telemetry used to read in site measurements.[3] Bridge instrumentation is conducted to check design specifications, determine the performance of emerging technology used in bridge building, verify and monitor the bridge construction. Strain Gauges has a long tradition in rail safety. It is used on rails to measure stress and strain.[5] Strain gauges measure axial tension or compression without any rail effect. The strain gauges will produce an alert in the event of an emergency, so maintenance can be completed early to reduce the effect on railways.

References

• [1] Hoffman K.,” An Introduction to Measurements using Strain Gauges”,

HBM GmbH, Darmstadt, 1989

• [2] Bathe K. J.”Finite Element Procedures”, Prentice Hall, New Jersey, 1989.
• [3] Cook R.D. “Concepts and applications of Finite Element Analysis”,

1. Wiley & Sons, New Jersey, 2002,.

• [4] Crisfield M.A, “Non-linear Finite Element Analysis of Solid and Structures”, J. Wiley & Sons, Chichester, 1991.
• [5] Stöcker H., “Nowoczesne kompendium fizyki”, PWN, Warszawa,2010
• [6] Zienkiwicz O.C,” The Finite Element Method Volume 2: Solid Mechanics”, Oxford,2000.