Damage evolution in dynamic deformation of silicon carbide

Abstract

AbstractÐDamage evolution was investigated in silicon carbide by subjecting it to dynamic deformation in (a) a compression Hopkinson±Kolsky bar (compressive stresses of 5 GPa), and (b) high-velocity impact under con®nement (compressive stresses of 19±32 GPa) by a cylindrical (rod) tungsten alloy projectile. Considerable evidence of plastic deformation, as dislocations and stacking faults, was found in the fractured specimens. A polytype transformation was observed through a signi®cant increase in the 6H±SiC phase at compressive stresses higher than 4.5 GPa (in the vicinity of the dynamic compressive failure strength). Profuse dislocation activity was evident in the frontal layer in the specimen recovered from the projectile impact. The formation of this frontal layer is proposed to be related to the high lateral con®ne-ment, imposed by the surrounding material. It is shown that plastic deformation is consistent with an analysis based on a ductility parameter D K C at y pc p ). The microstructural defects and their evolution were found to be dependent on the concentration of boron and aluminum, which were added as sintering aids. Several mechanisms are considered for the initiation of fracture: (a) dilatant cracks induced by mismatch in the eective elastic moduli between two adjacent grains, leading to internal tensile stresses and creating transgranular fracture. Finite element calculations show that high tensile stresses are generated due to elastic compatibility strains; (b) Zener±Stroh cracks nucleated by the piled up dislocations along grain boundaries, and resulting in intergranular fracture; (c) cracks due to existing¯aws connected with grain-boundary phases, voids, etc.; and (d) stress concentrations due to twinning and stacking faults. The high dislocation density observed in the impacted specimen is consistent with existing models of microplasticity. 7

Experimental investigation on the surface and subsurface damages characteristics and formation mechanisms in ultra-precision grinding of SiC

“…Figure 9d is an enlarged image of region "b" with the sample tilting at another orientation, showing SFs with weak contrast and some edge on dislocations at the ends of fringes (marked by arrows) and no twins microstructure inside the grains. Such faults are similar to the phenomenon obtained in the dynamically ruptured SiC-I fragments in modified split Hopkinson bars test, indicating one of the contributions for this portation of SFs is coming from the plastic deformation of the SiC workpiece [40]. They are formed by the motion of partial dislocations in the basal planes, leaving behind stacking errors in the perfect SiC crystals.…”

“…The former part is mainly responsible for governing the nucleation and propagations of the SFs and twinning, while under the influence of lateral stress a tensile stress was generated perpendicular to the compressive stress as proposed in Ref. [40].…”

Damage development in an armor alumina impacted with ductile metal spheres

“…Although the relationships between failure mechanisms and material properties during ballistic impact have been studied extensively [Ashby and Sammis 1990;Longy and Cagnoux 1989;Rhee et al 2001;Shih et al 2000], no consensus exists on exactly how hardness, toughness and strength affect ballistic performance. In regard to penetration resistance, hardness, H , is arguably the most important material property; a hard material is more effective than a soft one at deforming and eroding an impacting projectile.…”

A Survey of Compression Studies on Silicon Carbide (SiC)

“…Numbers are attached to each polytype according to the number of pair layers within the stack. These polytypes differ with respect to temperature at generation [5]. 2H-SiC and 3C-SiC are formed at 1773 and 1873 K, respectively.…”