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<p>The strain distribution is the outcome of material&#xa0;properties, frictional conditions and strain path changes. The magnitude of strain non-uniformity is characterised by the Strain Non-uniformity Index (SNI). This is also the spatial derivative of spatial strain gradient, indicating the sharpness of the strain peak. It does not matter by which process the strain distribution was obtained. Unlike usual failure criteria like the Forming Limit Diagram (FLD), Forming Limit Stress diagram (FLSD), etc., which are&#xa0;based on laboratory-scale samples and simple strain paths, a component-specific criterion like the&#xa0;SNI will be consistent with the material properties, forming conditions, many of which cannot be measured, and the acceptance criteria for the product. The SNI can be used to predict failure by necking and instability as local strain gradients become significant. In the present work on SNI in uniaxial tension, the Strain Non-Uniformity Index is based purely on intrinsic material properties, the process being devoid of friction, contact, bending effects, and significant deviations in the strain path. Threshold SNI was determined from strain distribution data captured using the DIC technique. The strain distribution data were analysed to obtain the SNI and its evolution with strain, and its correlation with intrinsic properties <i>n</i> and <i>m</i> was established. The strain at diffuse necking correlated well with that estimated from the SNI evolution.</p>

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Investigations on the Strain Non-Uniformity Index (SNI) in Uniaxial Tension

  • 期刊论文

  • 发表日期：

    2026年5月30日

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  • Prashant P Date,
  • Akhil Kumar Nallana

摘要

The strain distribution is the outcome of material properties, frictional conditions and strain path changes. The magnitude of strain non-uniformity is characterised by the Strain Non-uniformity Index (SNI). This is also the spatial derivative of spatial strain gradient, indicating the sharpness of the strain peak. It does not matter by which process the strain distribution was obtained. Unlike usual failure criteria like the Forming Limit Diagram (FLD), Forming Limit Stress diagram (FLSD), etc., which are based on laboratory-scale samples and simple strain paths, a component-specific criterion like the SNI will be consistent with the material properties, forming conditions, many of which cannot be measured, and the acceptance criteria for the product. The SNI can be used to predict failure by necking and instability as local strain gradients become significant. In the present work on SNI in uniaxial tension, the Strain Non-Uniformity Index is based purely on intrinsic material properties, the process being devoid of friction, contact, bending effects, and significant deviations in the strain path. Threshold SNI was determined from strain distribution data captured using the DIC technique. The strain distribution data were analysed to obtain the SNI and its evolution with strain, and its correlation with intrinsic properties n and m was established. The strain at diffuse necking correlated well with that estimated from the SNI evolution.