Finite element analysis of induced damage due to indentation and scratching on brittle materials

Grinding with diamond wheels is the primary process used in achieving high dimensional accuracy and desired surface integrity of structural ceramic components. However, the interaction between the grinding grits and the material is extremely complex to analyze due to the brittle nature of ceramics. To understand the material removal mechanisms during a high speed ceramic grinding process, two simplified approaches have been adopted in the literature: (1) experimental simulations including single and multi-grit scratch tests, and (2) modeling efforts utilizing static indentation fracture mechanics approach. The former approach typically measures the grinding forces and specific energy as well as microscopically observes the surface morphology and the grinding detritus. It allows for analyzing the inter-relationship between the material removal mechanisms and the associated process induced damage evolution modes. The latter approach models the interaction of an abrasive grit with the workpiece as an indentation event. The induced damage is then modeled as idealized crack systems produced by a sharp indenter. In these studies, the median cracks which develop during the loading phase represent the residual damage during the grinding process and the lateral cracks which develop during the unloading phase are viewed as responsible for material removal.; The induced damage due to indentation and scratching was found to depend on both the brittle nature of ceramics and the plastic behavior caused by high compressive stresses beneath the indenter.; To further understand the influence of plasticity on induced fracture patterns, an ‘elastic-plastic-cracking’ (EPC) model was developed and used to analyze the brittle fracture characteristics on materials subjected to Vickers indentation loads. The analysis indicated that the EPC model can capture the development of median cracks during the loading phase and the development of lateral cracks during the unloading phase of the Vickers indentation cycle. The influence of material properties (Young's modulus E, yield stress Y, fracture stress $sf$) on induced damage zone characteristics was analyzed by defining a non-dimensional brittleness parameter $EY/s2f1/3$. The model predictions of hardness as well as load-depth (P-h) relationship during an indentation cycle were found to agree well with the experimental trends presented elsewhere in the literature. (Abstract shortened by UMI.)...