通过钻孔理论进行残余应力测量
SINT 技术是一家位于意大利佛罗伦萨的公司，是 HBM 的合作伙伴, 设计开发的 MTS 3000, 是一种通过钻孔理论进行残余应力测试的自动系统.
残余应力 发生在任何机械结构中. 产生的原因，如焊接和塑性形变或材料的局部变形，材料表面的尖锐凹槽或者是敲击，或硬化等.
残余应力和机械应力对于机械结构来讲都一样重要. 但是，与机械应力可以通过加载来进行计算不同，因此，残余应力需要采用可靠的方法进行测量，而不能对表面产生大的破坏.
这也是钻孔理论产生的原因。通过在应变花的中心在材料表面钻个非常小的孔，通过检测在钻孔前后，应变花的变化，可以计算出残余应力的大小.
MTS 3000 系统包括:
- 一个光学-机械系统 (进行物理钻孔)
- 一个电子控制单元(控制光学-机械系统并通过HBM Spider8-30 放大器进行测量)
- 钻孔操作和控制软件 (进行自动钻孔)
- 后处理软件 (采用不同的评估理论来处理数据).
采用气涡轮进行钻孔，转速可达 400,000 RPM ，因此不会产生额外的残余应力.
后处理软件用来计算残余应力.
获得精确的应力状况，计算方法是非常重要的 许多研究者发表了很多钻孔理论计算应力的文献.
目前，在后处理软件中有三种计算方法: 均一应力理论, Kockelmann 理论和积分法 .
均一应力理论 [ASTM E 837-01标准]
这种理论在 ASTM E 837-01 标准中进行了详细描述, 是基于样本表面应力不伴随距离变化的假设为基础的. 因此，不考虑空间解析度. 如果残余应力是均一的，这是最好的计算方法，并且对测试错误不敏感.
Kockelmann’s method
Kockelmann’s method is based on the theory that there is a correlation function between the strain derivative and the stress distribution, expressed as a function of the hole’s depth. The bond is formed by a pair of coefficients (Kx and Ky), calculated on a simulation model, that relate stress and strain.
From these stress values it is possible to calculate the principal stresses and angle by using Mohr’s Circle.
Integral Method
This method, proposed by G. S. Schajer, provides a separate residual stress analysis at every hole-drilling depth increment. In this method, the contributions to the total measured strain relaxations of the stresses at all depths are considered simultaneously giving a higher spatial resolution than the other methods.
To simplify the problem of residual stress evaluation, Schajer proposed that the stress field could be described by means of step-wise functions whose value is constant through the partial hole depths. Using this hypothesis, Schajer established the numerical coefficients that are used for the calculation. The maximum depth that the method can be used for is 0.5 times the mean radius of the strain rosette used for the test.
The integral method should be chosen when residual stresses are expected to vary significantly with depth; however, it also has the highest sensitivity to test errors.
NEW! ASTM E837-08
There is a new standard on residual stresses that introduces the computation of non-uniform stresses. The Integral Method is used for this computation and the Tikhonov regularization can be used to reduce the errors in the calculated stresses when using a large number of hole depths.
