In strain-controlled fatigue testing, a conventional extensometer is usually used to measure the average strain between its two blades. However, the actual strain distribution in the gauge section cannot be revealed by the extensometer. To measure this distribution during strain-controlled fatigue testing of 304 stainless steel, stereo Digital Image Correlation (stereo-DIC) was used in this study. Three different geometries with two of them satisfying ASTM standard E606/E606M-12 were tested in strain-controlled fatigue testing with two representative strain amplitudes of ±1.0% and ±1.5% on a properly aligned testing machine. At both strain amplitudes, the two geometries in line with ASTM standard E606/E606M-12 exhibit evident nonuniform strain distribution under compression already from the very first cycle while the geometry proposed by the authors (not according to the ASTM standard E606/E606M-12) has better uniformity in axial strain distribution.

Next, a novel fixture is designed to monitor the misalignment of the specimens in the fatigue testing. Benefiting from the novel fixture and the stereo-DIC technique, not only the deformation in the gauge section of the specimen can be captured but also the misalignment between both ends of the specimen can be extracted by post-processing. The measured misalignment has been further used as boundary conditions in simulating the mechanical response of those three geometries under cyclic loading. Numerical simulation has successfully reproduced the nonuniform strain distribution under compression, which validates the stereo-DIC measurements. It suggests that while even following the ASTM standard E606/E606M-12, uniformity in strain distribution under compression cannot be ensured and thus might render the constitutive laws calibrated from strain-controlled fatigue testing invalid, since uniform stress and strain across the gauge section of the specimens were falsely assumed.

在应变控制疲劳测试中，通常使用传统的引伸计来测量其两个叶片之间的平均应变。然而，引伸计无法揭示测量截面中的实际应变分布。为了在 304 不锈钢的应变控制疲劳测试期间测量这种分布，本研究中使用了立体数字图像相关 (stereo-DIC)。三种不同的几何形状，其中两种满足 ASTM 标准 E606/E606M-12 在应变控制疲劳测试中进行了测试，在正确对齐的试验机上具有 ±1.0% 和 ±1.5% 的两个代表性应变幅度。在两个应变幅度下，

接下来，设计了一种新颖的夹具来监测疲劳试验中试样的错位。受益于新型夹具和立体DIC技术，不仅可以捕获试样量规截面的变形，还可以通过后处理提取试样两端之间的错位。测得的未对准已被进一步用作边界条件，以模拟这三种几何形状在循环载荷下的机械响应。数值模拟成功地再现了压缩下的非均匀应变分布，这验证了立体 DIC 测量。这表明即使遵循 ASTM 标准 E606/E606M-12，