Fatigue life prediction considering variability for additively manufactured pure titanium clasps.

PURPOSE: This study aims to develop a numerical prediction method for the average and standard deviation values of the largely varied fatigue life of additively manufactured commercially pure titanium (CPTi grade 2) clasps. Accordingly, the proposed method is validated by applying it to clasps of different shapes. METHODS: The Smith-Watson-Topper (SWT) equation and finite element analysis (FEA) were used to predict the average fatigue life. The variability was expressed by a 95% reliability range envelope based on the experimentally determined standard deviation. RESULTS: When predicting the average fatigue life, the previously determined fatigue parameters implemented in the SWT equation were found to be useful after conducting fatigue tests using a displacement-controlled fatigue testing machine. The standard deviation with respect to stroke and fatigue life was determined for each clasp type to predict variability. The proposed prediction method effectively covered the experimental data. Subsequently, the prediction method was applied to clasps of different shapes and validated through fatigue tests using 22 specimens. Finally, the fracture surface was observed using scanning electron microscopy (SEM). Many manufacturing process-induced defects were observed; however, only the surface defects where the maximum tensile stress occurred were crucial. CONCLUSIONS: It was confirmed that the fatigue life of additively manufactured pure titanium parts is predictable before the manufacturing process considering its variability by performing only static elasto-plastic FEA. This outcome contributes to the quality assurance of patient-specific clasps without any experimental investigation, reducing total costs and response time.

Tensile-shear properties of steel-Al adhesively bonded dissimilar joints and the effect of Al plate thickness.

Lap shear dissimilar joints between aluminium (Al) alloy, A6061-T6, and stainless steel, type 304, were fabricated by adhesive bonding. Three Al plates with different thicknesses were used to investigate the effect of the Al plate thickness on the tensile-shear properties, namely the effect of bending stiffness of Al plates. The maximum tensile-shear loads increased with increasing Al plate thicknesses. The fracture through the adhesive layer (cohesive fracture) occurred when the Al plate was the thickest, while the interface fracture between Al plate and adhesive layer appeared on the fracture surface with decreasing Al plate thickness. Fatigue strengths also increased with increasing Al plate thickness. When the fatigue strengths were normalized by the tensile strengths, the effect of the plate thickness became negligible. FEM analyses revealed that the stress concentration at the edge of adhesive on Al side decreased with increasing Al plate thickness, which could be related to the dependence of tensile and fatigue properties on the Al plate thickness.

Accumulation of high levels of free amino acids in soybean seeds through integration of mutations conferring seed protein deficiency.

Soybean ( Glycine max [L.] Merr.) seeds are rich in protein, most of which is contributed by the major storage proteins glycinin (11S globulin) and beta-conglycinin (7S globulin). Null mutations for each of the subunits of these storage proteins were integrated by crossbreeding to yield a soybean line that lacks both glycinin and beta-conglycinin components. In spite of the absence of these two major storage proteins, the mutant line grew and reproduced normally, and the nitrogen content of its dry seed was similar to that for wild-type cultivars. However, protein bodies appeared underdeveloped in the cotyledons of the integrated mutant line. Furthermore, whereas free amino acids contribute only 0.3-0.8% of the seed nitrogen content of wild-type varieties, they constituted 4.5-8.2% of the seed nitrogen content in the integrated mutant line, with arginine (Arg) being especially enriched in the mutant seeds. Seeds of the integrated mutant line thus appeared to compensate for the reduced nitrogen content in the form of glycinin and beta-conglycinin by accumulating free amino acids as well as by increasing the expression of certain other seed proteins. These results indicate that soybean seeds are able to store nitrogen mostly in the form of either proteins or free amino acids.