This study systematically investigates the effect of deviatoric loading paths on diffuse and localized deformation developing during the mechanical loading of a high porosity (20%) Vosges sandstone (Eastern France). Laboratory scale experiments are performed using a high pressure true triaxial apparatus, designed to provide access to full-field surface kinematics at high spatial and temporal resolutions during the loading phase. The true triaxial experiments, with independent control of the three principal stress, are conducted at two constant mean stresses, in the brittle-ductile transition regime, and at five prescribed Lode angles, from axisymmetric compression (ASC) to axisymmetric extension (ASE). First, the transition from diffuse towards localized deformation is analyzed in different loading increments and shows an intermediate step of early strain localization, characterized by a large number of early deformation bands developing well before the stress peak and with a predominantly dilatant behavior. Secondly, the evolution of the mechanical behavior and localization patterns, such as deformation band angles and localized dilatancy, indicate a transition from the brittle regime to the ductile regime that is not only dependent on an increase in the mean stress, but also on a decrease in the Lode angle. The analysis of full-field measurements also provides insights into the emergence and evolution of local strains, as deformation structures coalesce or relocate and different failure modes develop depending on the prescribed stress paths.

本研究系统地研究了在高孔隙度（20%）孚日砂岩（法国东部）机械加载过程中偏向加载路径对扩散和局部变形发展的影响。实验室规模的实验是使用高压真三轴装置进行的，该装置旨在在加载阶段以高空间和时间分辨率提供对全场表面运动学的访问。真正的三轴实验，独立控制三个主应力，在两个恒定平均应力下进行，从轴对称压缩（ASC）到轴对称扩展（ASE）。首先，在不同的加载增量下分析了从扩散到局部变形的转变，并显示了早期应变局部化的中间步骤，其特征是大量早期变形带在应力峰值之前形成，并且具有主要的膨胀行为。其次，力学行为和局部化模式的演变，例如变形带角度和局部剪胀，表明从脆性状态过渡延性状态不仅取决于平均应力的增加，还取决于 Lode 角的减小。全场测量分析还提供了对局部应变的出现和演变的见解，因为变形结构会合并或重新定位，并且根据规定的应力路径会发展出不同的失效模式。