Abstract To evaluate the fatigue life of Q420C steel welded joints, fatigue tests were performed on butt-welded joints, cross-butt-welded joints and cross-fillet-welded joints. The fatigue strength S-N curves of the joints were fitted. Then the formation and development of fatigue cracks were analyzed by fracture morphology. The fatigue properties of joints were compared with literature data and standard curves. The results showed that the fatigue test data of the three types of welded joints were roughly above the standard curves. Moreover, the fatigue strength of butt-welded joint was significantly higher than the calculated values of standards, indicating a large safety margin. The test value of cross-butt-welded joint was close to the calculated values of standards, so it is suggested to moderately reduce the standard values. In addition, all the three standards could well predict the fatigue life of cross-fillet-welded joint. The fracture morphology of the specimens showed the development process of fatigue damage, and the fatigue displacement curve and damage curve proved the formation of the fatigue fracture in specimens.

Abstract Q420 structural steel, which is widely used in transmission towers and offshore platform structures, has been studied less than other steels. However, fatigue failure of offshore platform structures can occur under repeated wave loads. The fatigue strength applied stress–number of cycles (S-N) curves of Q420C structural steel were obtained by performing static tensile tests and high-cycle fatigue tests, and the fatigue crack formation and development were investigated based on the fracture morphology. The steel fatigue lifetimes were compared with standard curves and those of steels with various strengths reported previously. The results showed that the fatigue failure of the specimen was typical, and the fracture surface could be divided into a crack initiation region, a propagation region, and a transient fracture region. The Q420C curve was above the BS7608:2014, GB50017-2017, and ANSI/AISC360-10 standard curves. The S-N curve specified in the standard is conservative for Q420C steel. The strength of the steel directly affected its fatigue properties, and the thickness of the steel plate had a significant effect on the fatigue properties.

The polymorphism in the gonadotropin-releasing hormone receptor (GnRHR) gene was detected by PCR single-strand conformational (PCR-SSCP) and DNA sequencing methods in 224 Boer goats. Two single nucleotide polymorphisms (SNPs), G891T and G757A, were found in the exon I of the goat GnRHR gene and their associations with litter size in Boer goats were evaluated. Association analysis showed that G891T and G757A had significant effects on litter size. In locus G891T, individuals with GT genotype had significantly larger litter sizes compared to GG genotype in the first and third parity. In locus G757A, ewes with GG genotype had significantly higher litter sizes than those of GA in the fourth parity. The present study primarily revealed an association between allele T at 891 locus of the GnRHR gene and high litter size in the first and third parity in Boer goats. These results provide evidence that the GnRHR gene may be significantly correlated with a high prolificacy in goats.

Two active mutations (A 781 G and A 1575 G) in growth hormone (GH) gene, and their associations with litter size (LS), were investigated in both a high prolificacy (Matou, n = 182) and a low prolificacy breed (Boer, n = 352) by using the PCR-RFLP method. Superovulation experiments were designed in 57 dams, in order to evaluate the effect of different genotypes of the GH gene on superovulation response. Two genotypes (AA and AB, CC and CD) in each mutation were detected in these two goat breeds. Neither BB nor DD homozygous genotypes were observed. The genotypic frequencies of AB and CC were significantly higher than those of AA and CD. In the third parity, Matou dams with AB or CC genotypes had significantly larger litter sizes than those with AA and CD (p < 0.05). On combining the two loci, both Matou and Boer dams with ABCD genotype had the largest litter sizes when compared to the other genotypes (p < 0.05). When undergoing like superovulation treatments, a significantly higher number of corpora lutea and ova, with a lower incidence of ovarian cysts, were harvested in the AB and CC genotypes than in AA and CD. These results show that the two loci of GH gene are highly associated with abundant prolificacy and superovulation response in goat breeds.