Particulate erosion of brittle materials is a complex process of fracture nucleation, growth, and interaction which leads to removal of material from the exposed surface. The temporal and spatial development of the localized pressure loading imparted to a material surface by a water-drop or soft-body collision is not clearly defined. For the impact conditions investigated, the duration of the applied pressure pulse is generally less than 100 ns. Correspondingly, the exact form of the transient stress states generated within the impacted body is not easily determined. However, insights into the nature of the damage produced by these relatively short stress cycles are being obtained from microscope examinations of the residual deformation and fracture patterns in transparent materials. The response of single crystals of magnesium oxide to water-drop collisions is described. It was found that for the high strain rates imposed slip and fracture occur in the same systems and planes as are associated with quasi-static deformations. However, water-drop impacts produce slip only on the four {110}45-deg slip systems, whereas rounded solid particles produce dominant slip on two {110} 90-deg slip systems, as well as on the {110} 45-deg slip systems. The fractures associated with each condition are also distinctly different. It was also found that fracture initiation could be suppressed with the introduction of numerous active slip sources on the impact face of the crystal.

Magnesium oxide crystals show a wide variety of deformation and fracture modes under tension at high temperatures depending on the number of slip systems operating concurrently in a given volume. At low temperatures slip is confined to a single 110 (110) system and plasticity is limited by stress concentrations which develop where slip switches from one plane to another. At intermediate temperatures 110 (110) slip systems at 90 degrees to each other can interpenetrate but those at 60 degrees cannot. At high temperatures dislocations can interpenetrate on all systems and polygonization can occur. After easy glide the crystals work harden and elongate over 100 percent before fracturing in a completely ductile manner. The transition from one mode to another depends on strain rate. The relative ability for 90 or 60 degree systems to intersect is discussed in terms of dislocation interactions. (Author).

Fracture: An Advanced Treatise, Volume VII: Fracture of Nonmetals and Composites examines the fracture of nonmetals and composites. The text of this treatise has been designed so that the reader may acquire pertinent information by self-study. Most chapters have been written in detail and, insofar as possible, have been made to fill a significant gap by also providing, when appropriate, the details of complicated and involved mathematical derivations in appendixes. Whenever possible, only a level of college calculus on the part of the reader has been assumed. Numerical examples showing the engineering applications have been included; also, photographs and drawings have been greatly utilized. The book opens with a review of the fracture behavior of glass. This is followed by separate chapters on the fracture of polymeric glasses; mechanics of the fracture process in rock, with emphasis on the engineering viewpoint; the fracture behavior of simple, single-phase ceramics; and empirical information about, and our level of understanding of, fracture in polycrystalline ceramics. Subsequent chapters deal with the fracture of elastomers; molecular mechanical aspects of the isothermal rupture of elastomers; failure mechanics of fibrous composites; fracture mechanics of composites; fracture and healing of compact bones; and fracture of two-phase alloys; and fracture of lake ice and sea ice.