Experimental Determination of Stress

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Region I：close to the crack tip is usually not a valid region for measuring the strain Region II：has a stress field that is dominated by the singular term, namely the stress intensity factor K.This is avalid area for determining strain field around the crack tip and thus K withrequired accuracy. Region III:is far away from the crack tip and needs complex analysis to obtain a stress intensity factor
STRAIN GAGE METHOD
• The strain gage also demonstrates all the optimum requirements of a strain measurement system, such as good stability with respect to temperature and time, accuracy of+1mm/m over a range of+5% strain, smaller gage length and width, minimal inertia, linear response and minimal skill requirement for installation and readout of the gage.In this method, the strain at a point near the crack tip is measured and is then used to determine K1 There are three basic electrical strain gages available; namely metal foil（金属箔）, semiconductor（半导 体）,and liquid metal gages（液态金属片）
Experimental Determination of Stress Intensity Factor K1 实验测定应力强度因子K1
experimental techniques
1 The strain gage method（应变片法） 2 Optical method of photoelasticity（光弹性的光学方法） 3 Shadow method of caustics（焦散阴影的方法） 4 Optical fiber sensors（光纤传感器） 5 Moire´ intephic interferometry（全息干涉法） 7 Coherent gradient sensing technique（相干梯度传感技术）