Sjödahl M
Appl Opt. 1995 Sep 1;34(25):5799-808. doi: 10.1364/AO.34.005799.
High-accuracy, noncontact measurements of in-plane strain fields have been performed through the use of an electronic-speckle-photography system. The strain fields are extracted from the displacement of defocused laser speckle in a telecentric imaging system. Two different illumination configurations have been suggested, both of which use four illumination directions. Both configurations produce results of an accuracy according to Me/ΔL, where M is the demagnification of the telecentric imaging system, e is the random error in the speckle-displacement fields, and ΔL is the magnitude of the defocusing distance. The maximum defocusing distance possible was found to be restricted by the spatial resolution, especially at high magnifications. In experiments on a semicircularly and a rectangularly notched aluminum sheet, the principal strain field around the notch was measured with a random error in the strain field of less than 10 µstrain (µm/m).
通过使用电子散斑摄影系统，已经实现了对面内应变场的高精度非接触测量。应变场是从远心成像系统中散焦激光散斑的位移中提取出来的。提出了两种不同的照明配置，这两种配置都使用四个照明方向。两种配置产生的结果精度均符合Me/ΔL，其中M是远心成像系统的缩小倍率，e是散斑位移场中的随机误差，ΔL是散焦距离的大小。发现可能的最大散焦距离受到空间分辨率的限制，尤其是在高放大倍率下。在半圆形和矩形缺口铝板的实验中，测量了缺口周围的主应变场，应变场中的随机误差小于10微应变（μm/m）。
