Effect of grinding on the fatigue life of titanium alloy (5 Al-2.5 Sn) under dry and wet conditions

The principal factors in the performance of aerospace materials are strength-to-weight ratio, fatigue life, fracture toughness, survivability and, of course, reliability. Machining processes and, in particular, grinding under adverse conditions have been found to cause damage to surface integrity and affect the residual stress distribution in the surface and subsurface region. These effects have a direct bearing on the fatigue life. In this investigation the effects of grinding conditions on the fatigue life of Titanium 5 Al-2.5Sn were studied. This alloy is used in ground form in the manufacturing of some critical components in the space shuttle's main engine. It is essential that materials for such applications be properly characterized for use in severe service conditions. Flat sub-size specimens 0.1 inch thick were ground on a surface grinding machine equipped with a variable speed motor at speeds of 2000 to 6000 rpm using SiC wheels of grit sizes 60 and 120. The grinding parameters used in this investigation were chosen from a separate study. The ground specimens were then fatigued at a selected stress and the resulting lives were compared with that of the virgin material. The surfaces of the specimens were examined under a scanning electron microscope, and the roughness and hardness were measured using a standard profilometer and microhardness tester, respectively. The fatigue life of the ground specimens was found to decrease with the increase in speed for both dry and wet conditions. The fatigue life of specimens ground under wet conditions showed a significant increase at the wheel speed of 2000 rpm for both the grit sizes and thereafter decreased with increase profilometry, microhardness measurements and scanning electron microscopic examination

Design and Implementation of an X-Ray Strain Measurement Capability Using a Rotating Anode Machine

This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). Residual stresses close to the surface can improve the reliability and lifetime of parts for technological applications. X-ray diffraction plays a significant role in gaining an exact knowledge of the stresses at the surface and their depth distribution. An x-ray capability at Los Alamos is key to developing and maintaining industrial collaborations in strain effects. To achieve this goal, the authors implemented a residual strain measuring station on the rotating anode x-ray instrument at the Lujan Center. This capability has been used to investigate residual strains in heat treated automotive components, machining effects on titanium alloys, resistance welded steel joints, titanium matrix fiber reinforced composites, ceramic matrix composites, thin films, and ceramic coatings. The overall objective is to combine both x-ray and neutron diffraction measurements with numerical models (e.g., finite element calculations)

A study of twinning in zirconium using neutron diffraction and polycrystalline modeling

An experimental study using neutron diffraction quantified the evolution of twinning in pure clock-rolled zirconium that was subsequently deformed under uniaxial compression. The clock rolling introduced an initial texture of approximately 5 times random, and the compression specimens were cut with their loading axes nearly parallel to the predominant c-axes direction. Seven specimens deformed to strains between ?2 and ?17 pct and an undeformed specimen (0 pct strain) were examined. The deformation was performed at an applied strain rate of 0.001/s at 77 K. Twin volume fractions were estimated from diffraction data. Changes in texture and twin volume fractions were compared to predictions from a visco-plastic self-consistent (VPSC) polycrystal model, which described both slip and twinning. This work demonstrates the feasibility of using neutron diffraction to track the evolution of twinning. These results help benchmark the polycrystalline model, validate the description of twinning, and potentially lead to a better understanding of its role in hardening.NRC publication: Ye

Investigations of the reduction of NiAl{sub 2}O{sub 4}. 2: X-ray diffraction studies

The volume shrinkage that accompanies the reduction of NiAl{sub 2}O{sub 4} to a metal-ceramic composite of nickel and alumina leads to residual stress buildup. The authors have attempted to utilize these stresses to temper a ceramic component by placing it under compression. To prove the concept, they produced model specimens which they investigated using X-ray diffraction. Employing the conventional d vs. sin{sup 2} {Psi} method to map surface stresses, the results obtained from these measurements are presented together with finite element calculation predictions used to interpret experimental stress data

Texture and residual strain in SiC/Ti-6-2-4-2 titanium matrix composites

Residual strain and texture variations were measured in two Titanium matrix composites reinforced with Silicon Carbide fibers (Ti/SiC) of similar composition but fabricated by different processing routes. Each composite comprised a Ti-6242 {alpha}/{beta} matrix alloy containing 35% by volume continuous SiC fibers. In one composite, the matrix was produced by a plasma spray (PS) route, and in the other by a wire drawing (WD) process. The PS and WD composites were reinforced with SCS-6 (SiC) and Trimarc (SiC) fibers, respectively. The texture in the titanium matrices differed significantly, from approximately {approx} 1.1x random for the monolithic and composite produced by PS route to {approx} 17x random in the monolithic and {approx}6x random in the composite produced by the WD route. No significant differences in matrix residual strains between the composites prepared by the two procedures were noted. The Trimarc (WD) fibers recorded higher ({approx}1.3x) compressive strains than the SCS-6 (PS) fibers in all the measured directions. The plane-specific elastic moduli, measured in load tests on the un-reinforced matrices, showed little difference

Association of calpain 10 gene polymorphisms with type 2 diabetes mellitus in Southern Indians

The aim was to investigate the association between the CAPN10 gene single nucleotide polymorphisms (SNPs) -44 (rs2975760), -43 (rs3792267), -19 (rs3842570), and -63 (rs5030952) and type 2 diabetes mellitus in an Asian Indian population in Southern India. A total of 1443 subjects, 794 normal glucose tolerant (NGT) and 649 type 2 diabetes mellitus subjects, were randomly selected from the Chennai Urban Rural Epidemiology Study. These subjects were genotyped for the 4 CAPN10 SNPs using polymerase chain reaction-restriction fragment length polymorphism and validated by direct sequencing. None of the 4 SNPs showed any significant differences in the genotypic distribution among the NGT and type 2 diabetes mellitus subjects (P=.20, .86, .34, and .39 for SNPs -44, -43, -19, and -63, respectively). The NGT subjects with the 11 genotype of the SNP -63 had significantly higher 2-hour postload plasma glucose (mean ± SD, 5.66 ± 1.05 mmol/L) levels compared with the combined 12 and 22 genotype group (5.33 ± 1.11 mmol/L, P=.004). The P value remained significant even after adjusting for age, sex, body mass index, smoking, and alcohol consumption (nominal P=.008). No significant difference in the biochemical parameters was observed when the subjects were stratified according to the other SNPs. The 2111 haplotype corresponding to SNPs -44, -43, -19, and -63 showed a significant difference in the proportion among NGT (0.18) and type 2 diabetes mellitus subjects (0.22, nominal P=.014). Although the Bonferroni correction based on the asymptotic test does not preserve this significance, the test based on the empirical distribution remained significant. In conclusion, our study raises the possibility that the 2111 haplotype of SNPs -44, -43, -19, and -63 may be associated with type 2 diabetes mellitus, although none of these SNPs may be individually associated with diabetes