Numerical Simulations of Void Linkage in Model Materials using a Nonlocal Ductile Damage Approximation

Experiments on the growth and linkage of 10 μm diameter holes laser drilled in high precision patterns into Al-plates were modelled with finite elements. The simulations used geometries identical to those of the experiments and incorporated ductile damage by element removal under the control of a ductile damage indicator based on the micromechanical studies of Rice and Tracey. A regularization of the problem was achieved through an integral-type nonlocal model based on the smoothing of the rate of a damage indicator D over a characteristic length L. The simulation does not predict the experimentally observed damage acceleration either in the case where no damage is included or when only a local damage model is used. However, the full three-dimensional simulations based on the nonlocal damage methodology do predict both the failure path and the failure strain at void linkage for almost all configurations studied. For the cases considered the critical parameter controlling the local deformations at void linkage was found to be the ratio between hole diameter and hole spacing

Study of the upper bound of tool edge radius in nanoscale ductile mode cutting of silicon wafer

10.1007/s00170-009-2347-6International Journal of Advanced Manufacturing Technology489-12993-999IJAT

In\ua0vitro degradation study of polyanhydride copolymers / surface grafted hydroxyapatite composites for bone tissue application

Poly (1,6-bis- (p-carboxyphenoxy hexane)-co- (sebacic anhydride)) (PANH), is a polyanhydride copolymer which has good biocompatibility, and degrades to non-toxic products with a predictable rate of degradation. Nano-sized hydroxyapatite (HAP) is a well-known biomaterial which has been applied in bone regeneration due to its osteoconductivity. However, nano-sized HAP has poor colloidal stability which leads to agglomeration when incorporated into polymeric composites. In this work we describe the surface grafting of poly(ɛ-caprolactone) to HAP (PCL-gHAP) to improve the interfacial adhesion and dispersion of HAP particles in a PANH matrix to form a composite material. The use of scanning electron microscopy-backscattered electron (SEM-BSE) detector and the combination of focused ion beam (FIB)/ transmission electron microscopy (TEM) provided a powerful approach for observing the dispersion of HAP particles in the polymer matrix. We show that surface modification of HAP with PCL improved the homogeneity of the dispersion of HAP particles in the composites and affected the composite morphology during hydrolytic degradation. Composites with high HAP content displayed high compressive strength and a fast rate of degradation. The PCL-gHAP/PANH composites showed superior maintenance of mechanical properties compared with HAP/PANH composites during degradation. A preliminary in\ua0vivo study on rat calvaria repair, demonstrated the superior performance of PCL-gHAP/PANH composites. The results suggest that the newly developed PCL-gHAP/PANH composite materials have great potential of serving as a new substrate for bone tissue engineering

Adenine auxotrophic heterozygosity in Candida krusei

Candida krusei CK18 carries heterozygosity for a recessive adenine biosynthesis allele, as it can be induced by UV irradiation to form adenine mutants at high frequency. The resultant mutants were characterized with the phenotype of red colony and residual growth on minimal media. The majority of the descendant prototrophic segregates were capable of continuous segregation to adenine mutants, suggesting gene conversion as one possible mechanism for the occurrence of the adenine auxotroph in the isolate.link_to_subscribed_fulltex