Fethma M. Nor

Finite element analysis of bone–implant biomechanics: refinement through featuring various osseointegration conditions

A refinement technique is proposed for developing finite element models capable of simulating peri-implant bone conditions for bone types II, III, and IV at various degrees of osseointegration. The refined models feature a transition region between bone (cortical and cancellous) and implant and designate it partially to fully osseointegrated by assigning corresponding fractions of the bulk bones elastic properties to this region. Bone is assumed to be transversely isotropic. The refined technique is implemented in a case study, in which osseointegrated (25-100%) peri-implant bone, type II, III, or IV with an implant attached, is loaded with a 100 MPa occlusal load. The biomechanics of this peri-implant bone was simulated and analysed. Results showed that the less dense bone must support higher stress and strain, especially at the cortical region. Higher degree of osseointegration induced higher stress but lower strain. Both the bone type and the osseointegration condition significantly affected the stress-strain relation. For minimum stress and strain, denser and more osseointegrated peri-implant bone is desirable. When bone failure criteria were set, based on the yield strength and strain of the bone, a higher degree of osseointegration was needed for the less dense peri-implant bone to be considered safe.

Elastic properties of polycaprolactone at small strains are significantly affected by strain rate and temperature

Tensile tests were conducted on polycaprolactone at various strain rates and temperatures. Focusing on the mechanical properties within only the small-strain elastic region, i.e. up to the inflection point in the stress–strain diagram, it was found that strain rate and temperature had significant effects on the polymer. This finding implies that the effects of strain rate and temperature on the elastic properties of polycaprolactone should be considered in the design and manufacture of rigidity-sensitive, load-bearing applications, including use as biomaterial for scaffolds in tissue engineering applications.

Polycaprolactone–starch blends with corn-based coupling agent: physical properties and in vitro analysis

In an attempt to improve properties of polycaprolcatone–starch blend, this study uses zein as coupling agent in preparing the blend through a single-step process. Zein, which has affinity to both polar and non-polar groups, is expected to improve miscibility between the blends’ constituents and its overall biocompatibility. Mechanical properties of the blend were tested and further characterizations (Fourier transform infrared spectroscopy, thermal properties) were performed to analyze the effect of zein as an addition to the blend’s physical properties. The blend’s biocompatibility was examined by indirect methods (contact angle and weight gain after immersion in simulated body fluid) and in vitro analysis. No significant effect on the blend’s strength and stiffness was caused by adding zein. Hydrophilicity and cell affinity were improved when zein was added. Zein did not perform as a coupling agent that improved miscibility between polycaprolactone and starch, but its addition improved the blend’s biocompatibility.

Hybrid Experimental-Computational Approach for Solder/IMC Interface Shear Strength Determination in Solder Joints

Damage-based models for solder/intermetallics (IMC) interface often require the interface properties such as tensile and shear strengths. The minute size of the solder joint renders direct experimental determination of these properties impractical. This paper presents a hybrid experimental-computational approach to determine the shear strength of solder/IMC interface. Displacement-controlled ball shear tests are performed on as-reflowed and thermally-aged solder specimens. The observed sudden load drop in the load-displacement curve corresponds to the crack initiation event and the load is indicative of the shear strength of the solder/IMC interface. Finite element simulation of the ball shear test is then employed to establish the complex stress states at the interface corresponding to the onset of fracture. The finite element model consists of Sn40Pb solder, Ni3Sn4 intermetallic and Ni layers, copper pad and a rigid shear tool. Unified inelastic strain theory describes the strain rate-dependent response of the solder while other materials are assumed to behave elastically. Quasi-static ball shear test is simulated at 30°C with a prescribed displacement rate of 0.5mm/min. Results show that steep stress gradients develop in the shear tool-solder contact and solder/IMC interface regions indicating effective load transfer to the interface. The bending (normal) stress is found to be of the same order of magnitude as the maximum shear stress. Higher stress values are predicted near the leading edge of the solder/IMC interface. The equivalent shear stress condition to the triaxial stress state at the interface, represented by the absolute maximum shear stress, τmax,abs should have reached the shear strength of the interface at fracture. The resulting shear strength of Sn40Pb/Ni3Sn4 interface is determined to be 87.5 MPa.

Strain rate and temperature effects on elastic properties of polycaprolactone/starch composite

Abstract Composite of polycaprolactone (PCL) and starch is a potential biomaterial for tissue engineering scaffolds. During implantation, its mechanical properties might be compromised considering the various strain rates it is subjected to and that human body temperature is close to polycaprolactone’s melting temperature. This study aims at revealing the effect of strain rate and temperature to the elastic properties of polycaprolactone-starch composite. Tensile test at strain rates of 5, 0.1, and 0.01 mm/min at ambient and body temperatures were performed. It was revealed that strain rate as well as temperature readily have significant effects on the composite’s elastic properties. Such effects have similar trends with that of PCL homopolymer which is used as the composite’s matrix. Further analysis on the consequence of the finding was performed by applying the behavior to a finite element model of a porous scaffold and it was found that the discrepancy in elastic properties throughout the construct is even greater.

Effect of starter defect to GIIC of unidirectional CFRP composite

Critical strain energy release rate in CFRP composites characterizes the delamination resistance. More study is still needed to measure the critical strain energy release rate in sliding shear mode (GIIC) considering various factors that influence its measurement. This study evaluates one of the influencing factors, the starter defect. Two types of on thin, unidirectional CFRP composites with one having thin film insert as starter defect and another one with pre-crack under Mode II loading were prepared and tested in three point bending end notch flexure (3ENF) test. It was found that the (GIIC) of the former was more than twice higher than that of the latter, supposedly due to the presence of resin rich region in the former.