The influence of mechanical properties of powder steels on die’s durability

Представлені результати експериментальних досліджень механічних властивостей сучасних штампових сталей для виготовлення карбувальних штемпелів з метою їх порівняння для обґрунтованого вибору. Були проведені дослідження штампових сталей К455 та Vanadis-4 Extra на статичну міцність в умовах триточкового згину, визначена ударна в’язкість на зразках з V-подібним концентратором, а також за результатами втомних випробувань була побудована крива втоми та встановлена границя витривалості при симетричному циклі для сталі К455. Всі випробування проводилися за стандартними методиками на зразках, що пройшли термообробку за технологією, яка застосовується при виготовленні карбувальних штемпелів. Були також проведені натурні випробування штемпелів з вказаних матеріалів з визначенням їх тиражостійкості з обґрунтуванням отриманих результатів на основі аналізу хімічного складу, структури матеріалів та експериментально встановлених характеристик статичної і динамічної міцності.The results of experimental studies of the mechanical properties of modern die steels for the manufacture of stamping dies for the purpose of comparing them to make informed choices. Die steels K455 and Vanadis-4 Extra were studied to obtain static strength characteristics in a three-point bending, identified toughness on specimens with V-like hub, as well as the results of fatigue tests were described with fatigue curve and fatigue point at symmetrical cycle was estimated for steel K455. All tests were conducted using standard techniques on specimens heat treated on the technology used in the manufacture of stamping dies. There were also conducted field tests of stamps powder steel Vanadis-4 Extra with the definition of plate run. Actual tests of stamping dies were conducted to identify their plate run with the justification of the results based on the analysis of the chemical composition, structure and materials experimentally determined characteristics of static and dynamic strength.Представлены результаты экспериментальных исследований механических свойств современных штамповых сталей для изготовления чеканочных штемпелей с целью их сравнения для обоснованного выбора. Были проведены исследования штамповых сталей К455 и Vanadis-4 Extra на статическую прочность в условиях трехточечного изгиба, определена ударная вязкость на образцах с V-подобным концентратором, а также по результатам усталостных испытаний была построена кривая усталости и установлен предел выносливости при симметричном цикле для стали К455. Все испытания проводились по стандартным методикам на образцах, прошедших термообработку по технологии, применяемой при изготовлении чеканочных штемпелей. Были также проведены натурные испытания штемпелей из порошковой стали Vanadis-4 Extra с определением их тиражестойкости. Проведено обоснование полученных результатов на основе анализа химического состава, структуры материалов и экспериментально установленных характеристик статической и динамической прочности

Genetic Effects on Bone Loss in Peri- and Postmenopausal Women: A Longitudinal Twin Study

This longitudinal twin study was designed to assess the heritability of bone loss in peri- and postmenopausal women. A sample of 724 female twins was studied. Baseline and repeat BMD measurements were performed. Results of genetic model-fitting analysis indicated genetic effects on bone loss account for similar to 40% of the between-individual variation in bone loss at the lumbar spine, forearm, and whole body. Introduction: BMD and bone loss are important predictors of fracture risk. Although the heritability of peak BMD is well documented, it is not clear whether bone loss is also under genetic regulation. This study was designed to assess the heritability of bone loss in peri- and postmenopausal women. Materials and Methods: A sample of 724 female twins (177 monozygotic [MZ] and 185 dizygotic [DZ] pairs), 45-82 yr of age, was studied. Each individual had baseline BMD measurements at the lumbar spine, hip, forearm, and total body by DXA and at least one repeat measure, on average 4.9 yr later. Change in BMD (Delta BMD) was expressed as percent of gain or loss per year. Intraclass correlation coefficients for ABMD were calculated for MZ and DZ pairs. Genetic model-fitting analysis was conducted to partition the total variance of ABMD into three components: genetic (G), common environment (C), and specific environment, including measurement error (E). The index of heritability was estimated as the ratio of genetic variance over total variance. Results: The mean annual Delta BMD was -0.37 +/- 1.43% (SD) per year at the lumbar spine, -0.27 +/- 1.32% at the total hip, -0.77 +/- 1.66% at the total forearm, -0.36 +/- 56% at the femoral neck, and -0.16 +/- 0.81% at the whole body. Intraclass correlation coefficients were significantly higher in MZ than in DZ twins for all studied parameters, except at the hip sites. Results of genetic model-fitting analysis indicated that the indices of heritability for ABMD were 0.38, 0.49, and 0.44 for the lumbar spine, total forearm, and whole body, respectively. However, the genetic effect on ABMD at all hip sites was not significant. Conclusions: These data suggest that, although genetic effects on bone loss with aging are less pronounced than on peak bone mass, they still account for similar to 40% of the between-individual variation in bone loss for the lumbar spine, total forearm, and whole body in peri- and postmenopausal women. These findings are relevant for studies aimed at identification of genes that are involved in the regulation of bone loss

Genetic Effects on Bone Loss in Peri- and Postmenopausal Women: A Longitudinal Twin Study

This longitudinal twin study was designed to assess the heritability of bone loss in peri- and postmenopausal women. A sample of 724 female twins was studied. Baseline and repeat BMD measurements were performed. Results of genetic model-fitting analysis indicated genetic effects on bone loss account for similar to 40% of the between-individual variation in bone loss at the lumbar spine, forearm, and whole body. Introduction: BMD and bone loss are important predictors of fracture risk. Although the heritability of peak BMD is well documented, it is not clear whether bone loss is also under genetic regulation. This study was designed to assess the heritability of bone loss in peri- and postmenopausal women. Materials and Methods: A sample of 724 female twins (177 monozygotic [MZ] and 185 dizygotic [DZ] pairs), 45-82 yr of age, was studied. Each individual had baseline BMD measurements at the lumbar spine, hip, forearm, and total body by DXA and at least one repeat measure, on average 4.9 yr later. Change in BMD (Delta BMD) was expressed as percent of gain or loss per year. Intraclass correlation coefficients for ABMD were calculated for MZ and DZ pairs. Genetic model-fitting analysis was conducted to partition the total variance of ABMD into three components: genetic (G), common environment (C), and specific environment, including measurement error (E). The index of heritability was estimated as the ratio of genetic variance over total variance. Results: The mean annual Delta BMD was -0.37 +/- 1.43% (SD) per year at the lumbar spine, -0.27 +/- 1.32% at the total hip, -0.77 +/- 1.66% at the total forearm, -0.36 +/- 56% at the femoral neck, and -0.16 +/- 0.81% at the whole body. Intraclass correlation coefficients were significantly higher in MZ than in DZ twins for all studied parameters, except at the hip sites. Results of genetic model-fitting analysis indicated that the indices of heritability for ABMD were 0.38, 0.49, and 0.44 for the lumbar spine, total forearm, and whole body, respectively. However, the genetic effect on ABMD at all hip sites was not significant. Conclusions: These data suggest that, although genetic effects on bone loss with aging are less pronounced than on peak bone mass, they still account for similar to 40% of the between-individual variation in bone loss for the lumbar spine, total forearm, and whole body in peri- and postmenopausal women. These findings are relevant for studies aimed at identification of genes that are involved in the regulation of bone loss

Genome-Wide Association Study Using Extreme Truncate Selection Identifies Novel Genes Affecting Bone Mineral Density and Fracture Risk

Osteoporotic fracture is a major cause of morbidity and mortality worldwide. Low bone mineral density (BMD) is a major predisposing factor to fracture and is known to be highly heritable. Site-, gender-, and age-specific genetic effects on BMD are thought to be significant, but have largely not been considered in the design of genome-wide association studies (GWAS) of BMD to date. We report here a GWAS using a novel study design focusing on women of a specific age (postmenopausal women, age 55–85 years), with either extreme high or low hip BMD (age- and gender-adjusted BMD z-scores of +1.5 to +4.0, n = 1055, or −4.0 to −1.5, n = 900), with replication in cohorts of women drawn from the general population (n = 20,898). The study replicates 21 of 26 known BMD–associated genes. Additionally, we report suggestive association of a further six new genetic associations in or around the genes CLCN7, GALNT3, IBSP, LTBP3, RSPO3, and SOX4, with replication in two independent datasets. A novel mouse model with a loss-of-function mutation in GALNT3 is also reported, which has high bone mass, supporting the involvement of this gene in BMD determination. In addition to identifying further genes associated with BMD, this study confirms the efficiency of extreme-truncate selection designs for quantitative trait association studies

Contribution of a Common Variant in the Promoter of the 1-α-Hydroxylase Gene (CYP27B1) to Fracture Risk in the Elderly

CYP27B1 encodes mitochondrial 1α-hydroxylase, which converts 25-hydroxyvitamin D to its active 1,25-dihydroxylated metabolite. We tested the hypothesis that common variants in the CYP27B1 promoter are associated with fracture risk. The study was designed as a population-based genetic association study, which involved 153 men and 596 women aged 65–101 years, who had been followed for 2.2 years (range 0.1–5.5) between 1999 and 2006. During the follow-up period, the incidence of fragility fractures was ascertained. Bone ultrasound attenuation (BUA) was measured in all individuals, as were serum 25-hydroxyvitamin D and PTH concentrations; 86% subjects had vitamin D insufficiency. Genotypes were determined for the –1260C>A (rs10877012) and +2838T>C (rs4646536) CYP27B1 polymorphisms. A reporter gene assay was used to assess functional expression of the –1260C>A CYP27B1 variants. The association between genotypes and fracture risk was analyzed by Cox’s proportional hazards model. We found that genotypic distribution of CYP27B1 –1260 and CYP27B1 +2838 polymorphisms was consistent with the Hardy-Weinberg equilibrium law. The two polymorphisms were in high linkage disequilibrium, with D′ = 0.96 and r2 = 0.94. Each C allele of the CYP27B1 –1260 polymorphism was associated with increased risk of fracture (hazard ratio = 1.34, 95% CI 1.03–1.73), after adjustment for age, sex, number of falls, and BUA. In transient transfection studies, a reporter gene downstream of the –1260(A)-containing promoter was more highly expressed than that containing the C allele. These data suggest that a common but functional variation within the CYP27B1 promoter gene is associated with fracture risk in the elderly