Strain gauge reinforcement of plastics

A major disadvantage in strain gauge work on plastics is the effect of strain gauge reinforcement, which induces signifcant errors in the quantitative evaluation of strain derived from the plastic. The parameters influencing reinforcement are well documented and procedures have been developed that permit the identification and correction of this effect in certain situations. The principal causes, effects and corrective procedures are reviewed and where appropriate compared with results obtained by the authors of this article.     

Strain gauge readings on a programmable pocket calculator

Programs and command instructions are described for three readily available and established programmable pocket calculators which are an aid to the reduction of readings for rosette strain gauges both into principal strains and stresses, and also to the corresponding maximum shear stresses.     

Strain gauge performance during fatigue testing

Strain gauges are used extensively to measure the changes in magnitude and distribution of dynamic stresses during fatigue testing. Over 200 000 fatigue cycles at high strains (4000 ± 2000/u/m) have to be withstood under certain conditions such as when evaluating the performance of heavy vehicle springs. In this work, various types of commercial strain gauges have been evaluated to determine the most appropriate installation for severe applications.
The best results were obtained using a constantan metal foil element strain gauge with phenolic glass backing.
Tests on heavy vehicle, multi-leaf, Taperlite springs, manufactured by Tinsley Bridge Limited (formerly BSC Light Products), have demonstrated the suitability of the chosen system and showed that the dynamic stresses remained essentially constant during fatigue testing.     

Neutron Strain measurement

The use of neutrons has extended the technique of diffraction strain measurement from an essentially two-dimensional, near-surface tool using X-rays to a true three-dimensional method. The depth scale has gone from micrometres to millimetres. This initially gave rise to subsurface measurements of type I residual macrostresses in weldments and type II residual microstresses in anisotropic and multiphase metals, and composites. Soon the possibilities of in situ applied stress measurements became apparent and today they represent a significant portion of the work being carried out. This perspective focuses on the current state of the art, the prospects and developments necessary for further progress. The transition from two- to three-dimensions raised the issues of stress free reference values, methodology for general tensor measurements, beam optics and experimental design. Workers invested great effort in resolving these issues. In addition, the development of pulsed source instruments has enabled in situ measurements of slip, fatigue, load partitioning, twinning, high T stress-strain response, thermal cycling and the shape memory effect. Most recently, the SNS instrument, VULCAN, has introduced torsion and continuous recording of data which can later be binned in the shortest statistically significant time intervals.     

Strain gauge installation in a civil engineering site

Installurion of resistance strain gauges is described for field tests under conditions of high humidity and in water in the intake area of a water power plant in New Zealand.     

technical note: Strain gauge slip ring circuits

This note describes practical uses of high quality slip rings for strain gauge measurements on rotating machinery. The advantages and disadvantages of various circuits are discussed and recommendations made for the best performance. Consideration is given to the most efficient use of the number of slip rings in a given system for the maximum data which can be obtained avoiding errors caused by slip ring noise. Other parameters which are considered are: the voltage applied to the bridge; the number of rings used to deliver power to the strain gauges and the gauge resistance. Some practical information on slip ring noise, life and cross talk and how to reduce it in the Chevron Bridge Circuit is also discussed.