Abstract The deposition of a hard coating is a commonly used solution to increase the scratch resistance of soft polymeric materials at low and moderate normal loads. But the major risk for a coating subjected to tribological stresses is to crack and spall off. In this study, the influence on scratch behavior of a hard polyurethane coating on a plasticized PVC substrate has been investigated. At low load, the hard coating allows decreasing the plastic deformation of the substrate, and a geometrical interpretation is proposed. At increasing loads, this coating shows three fracture mechanisms: first, cracks oriented at 45° to the scratch direction starting near the detachment point behind the tip, on the edge of the scratch; then, in addition to this first mechanism, tearing under the tip forming a central crack parallel to the scratch direction; finally, in addition to the first two mechanisms, a circular crack forms ahead of the indentor by a bending effect at the top of the frontal bulge. These mechanisms are observed in situ thanks to a microscope coupled to a camera. Then, the scratches are observed by X-Ray tomography in order to analyze crack propagation in the depth of the material. Finally a numerical model of the scratch test has been developed. The combination of the three techniques gives a precise insight into the local mechanical conditions that lead up to these different kinds of scratches.

中文翻译：

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硬对软聚合物双层的抗划伤性研究：原位视觉、X 射线断层扫描和数值模拟的结合

摘要 硬涂层的沉积是提高软聚合物材料在低和中等法向载荷下的抗划伤性的常用解决方案。但涂层承受摩擦应力的主要风险是开裂和剥落。在这项研究中，研究了硬质聚氨酯涂层在增塑 PVC 基材上的划痕行为的影响。在低负荷下，硬涂层可以减少基材的塑性变形，并提出了几何解释。在负载增加时，该涂层显示出三种断裂机制：首先，裂纹与划痕方向成 45°，从尖端后面的分离点附近开始，在划痕的边缘；然后，除了第一种机制之外，在尖端下方撕裂形成平行于划痕方向的中央裂缝；最后，除了前两种机制外，通过前凸出顶部的弯曲效应，在压头前方形成圆形裂纹。由于显微镜与相机相连，可以在原位观察到这些机制。然后，通过 X 射线断层扫描观察划痕，以分析材料深处的裂纹扩展。最后开发了划痕试验的数值模型。这三种技术的结合可以精确洞察导致这些不同类型划痕的局部机械条件。通过 X 射线断层扫描观察划痕，以分析材料深处的裂纹扩展。最后开发了划痕试验的数值模型。这三种技术的结合可以精确洞察导致这些不同类型划痕的局部机械条件。通过 X 射线断层扫描观察划痕，以分析材料深处的裂纹扩展。最后开发了划痕试验的数值模型。这三种技术的结合可以精确洞察导致这些不同类型划痕的局部机械条件。