Creep-fatigue crack growth testing and analysis of pre-strained 316H stainless steel

Material pre-straining is known to have significant effects of the mechanical response and crack growth behaviour of steels. In this paper, the influence of material pre-straining on the subsequent creep-fatigue crack growth behaviour of Type 316H stainless steel at 550 °C has been examined by performing tests on compact tension specimens that were extracted from blocks uniformly pre-compressed at room temperature. Creep-fatigue crack growth tests on pre-compressed material were performed at the frequency of 0.01 Hz and R-ratio of 0.1. The crack growth data obtained from these experiments have been correlated with the C* and K fracture mechanics parameters and the results are compared with the existing creep crack growth data on the pre-compressed and as-received material at 550 °C. The results obtained have also been compared with the creep-fatigue data from experiments on weldments where the crack tip was located in the heat affected zone (HAZ). The crack growth behaviour in creep-fatigue tests on pre-compressed material has been found similar to that of HAZ material and are higher than that of the as-received material. Moreover, depending on the loading condition and frequency the crack growth data obtained from creep-fatigue tests on pre-compressed material may be characterized using C* or ΔK fracture mechanics parameters

Association of candidate genes and molecular markers with male reproductive traits and meat quality properties in boer and boer cross goats

Boer goats are popularly reared in Malaysia as pure breed or as crosses with the local goat populations. As such, identification of the factors influencing their meat production and reproduction is necessary in order to design optimal breeding and selection programs. Conventional selection methods are usually costly for traits which are expressed later in life and evaluated in adulthood, and may be inappropriate when animals need to be sacrificed for such evaluation to be carried out. Using candidate genes in the selection criteria for male reproduction traits may allow early selection thus decreasing the rearing cost, decrease generation interval and increase accuracy of selection. It is more important in the selection for meat quality traits as animals need not be slaughtered to confirm their genetic merit for these traits, thus making them available for breeding. This study aimed to identify and elucidate the effects of functional candidate genes as well as non genetic factors on meat and semen quality traits in Boer goats and Boer crosses. This objective was accomplished through two independent studies. In the first study, fresh and thawed 1-day and 6-month frozen semen from 36 Boer bucks and 17 Boer crosses were evaluated. The semen quality traits were analyzed for the effects of fixed factors and 17 candidate genes chosen based on their physiological or biological functions. The effects of age, population,cryopreservation period and some of their interactions on the semen quality traits were significant (P<0.05). Sperm motility and average velocity were 44.16 % and 96.35 μm/s, respectively, after cryopreservation for 1 day, and 37.61 % and 90.04 μm/s, respectively, after 6 months. The younger goats showed higher sperm motility (43.32 %) for fresh and (38.45 %) for post-thaw semen after six months than older bucks. Restriction fragment length polymorphism (PCR-RFLP) and single strand conformation polymorphism (SSCP) analysis and comparative sequencing revealed three single nucleotide polymorphisms (SNP) in exon 3 of follicle stimulating hormone beta (FSHB), 200A>G (FSHB3-1), 226T>C (FSHB3-2) and 237A>G (FSHB3-3); two SNPs in the coding region of heat shock protein 70 (HSP70),73A>C (HSP70-1) and 190C>G (HSP70-2); one SNP in exon 2 of Luteinizing hormone beta (LHB) (207T>C) (LHB2); and one SNP in 5‘-UTR of neuropeptide Y (NPY) (182G>T) gene. There was also an indel in position 29 of NPY3. Analyses of variance revealed significant association of the candidate genes with libido and semen quality traits. The three SNPs of FSHB3 had significant effect on libido (P<0.05), progressive motility and abnormality of fresh semen (P < 0.05), and on motility, velocity and viability traits of post-thaw semen (P < 0.05). The SNPs of HSP70 were associated with libido, semen volume (VOL), sperm concentration (SCON), motility traits and sperm viability of fresh semen (P<0.05) and with motility and viability traits of post-thaw semen (P<0.05). The two SNPs of NPY gene influenced libido (P<0.05), progressive motility (PROG) of fresh semen (P<0.05), and motility traits, velocity traits, amplitude lateral sperm head (ALH), straightness (STR), linearity (LIN) and acrosome integrity (ACI) of post-thaw semen (P<0.05). In the second study, carcass characteristics and meat quality traits of 30 Boer goats,which were either not transported or transported in low or high stocking density before slaughter, were evaluated. The effects of non genetic factors and 24 candidate genes chosen for their known physiological or biological functions were investigated. The effects of aging, transportation and muscle types and their interactions were significant on meat quality traits (PC (HSP70-1) and 190CC (HSP27b-1) and 132C>G (HSP27b-2). Analyses of variance showed significant association of GH4-HaeIII with carcass dressing percentage (P < 0.05); the two SNPs of HSP70 were associated with pH, glycogen content, drip loss, cooking loss,redness (a*) and chroma (P<0.05); while the two SNPs of HSP27b-1 were associated with calpastatin level and drip loss shear force (P<0.05). The results of the present study shows there are candidate genes associated with semen quality as well as carcass and meat quality traits of Boer goats and Boer crosses. These genes may be targeted and used in marker assisted selection for the respective traits to improve the production and reproduction performance of the animals

Relevance of fracture mechanics to creep crack growth

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An investigation of irregular crack path effects on fracture mechanics parameters using a grain microstructure meshing technique

Electronic version of an article published as Journal of Multiscale Modeling, Vol. 4, Iss. 1, atricle 1250001, 2012, http://dx.doi.org/10.1142/S1756973712500011 © World Scientific Publishing Company, http://www.worldscientific.com/worldscinet/jmmA sub-grain size finite element modelling approach is presented in this paper to investigate variations in fracture mechanics parameters for irregular crack paths. The results can be used when modelling intergranular and transgranular crack growth where creep and fatigue are the dominant failure mechanisms and their crack paths are irregular. A novel method for sub-grain scale finite element mesh consisting of multiple elements encased in ~50–150 μm-sized grains has been developed and implemented in a compact tension, C(T), mesh structure. The replicated shapes and dimensions were derived from an isotropic metallic grain structure using representative random sized grain shapes repeated in sequence ahead of the crack tip. In this way the effects of crack tip angle ahead of the main crack path can be considered in a more realistic manner. A comprehensive sensitivity analysis has been performed for elastic and elastic-plastic materials using ABAQUS and the stress distributions, the stress intensity factor and the J-integral have been evaluated for irregular crack paths and compared to those of obtained from analytical solutions. To examine the local and macroscopic graph path effects on fracture mechanics parameters, a few extreme cases with various crack-tip angles have been modelled by keeping the macroscopic crack path parallel to the axis of symmetry. The numerical solutions from these granular mesh structures have been found in relatively good agreement with analytical solutions

Perceived Justice With Service Recovery, Recovery Satisfaction And Loyalty In An Airline Company: The Moderating Role Of Failure Attributions

It is now well documented that an effective recovery is an essential part of firms‟ service quality programs and critical to generating satisfaction and loyalty. A number of studies have investigated the impact of recovery efforts on post-recovery satisfaction, mostly in Western countries. However, despite the importance of customer attributions of service failure; the impact of customers‟ stability and controllability attributions of failure in implementing effective recovery programs is still under study. Based on Justice Theory, this research conducted in Malaysia employed a field study to investigate how customer evaluations of recovery efforts are influenced by interplay of their failure attributions and service recovery efforts of distributive, procedural, interactional and informational justices in the context of airline company. The findings resulted from the structured questionnaire collected among 263 respondents revealed that there is a significant relationship between perceived justice and recovery satisfaction as well as loyalty in distributive and procedural justices. Recovery satisfaction was found to be affecting loyalty. The results of hierarchical regression and inclusion of failure attributions as moderator found that positive relationship between procedural and informational justices and recovery satisfaction will be higher when stability and controllability of failure is low. Finally, recovery satisfaction mediated the relationship between perceived justice in distributive and procedural justices and loyalty. The results have implication for marketing theory as well as managerial action

Plastic pre-compression and creep damage effects on the fracture toughness behaviour of Type 316H stainless steel

The influence of inelastic damage in the form of plastic pre-strain and creep damage, on fracture toughness of Type 316H stainless steel has been examined. Creep damage has been introduced into the 8% pre-compressed material by interrupting creep crack growth tests. Comparisons have been made between the fracture toughness test results from the as-received, pre-compressed and creep damaged materials. Furthermore, the effects of creep crack discontinuities on the crack tip strain fields have been examined by digital image correlation measurements. Inelastic damage was found to reduce the fracture toughness of the material, with creep damage having more severe effects than pre-strain