Damage and failure mechanism of pre-static loaded rock under cyclic impact

To study the damage and failure mechanism of rocks under the coupling effect of high ground stress static load and cyclic impact disturbance generated by mining and excavation, the multi-strain rate dynamic static superposition rock mechanics test system was used to carry out the experiments with different pre-imposed static loads (0.45/0.65/0.85σc) superimposed cyclic impact and the same pre-imposed static load superimposed with cyclic impact loads of different frequencies (0.5/1.0/2.0 Hz). The experimental results indicate that the peak strength of rocks in the dynamic static superposition test is smaller than that in the static load test, and the maximum deformation is greater than that in the static load test, indicating that the dynamic static superposition load has a significant promoting effect on rock damage. The evolution of strength, deformation, and failure under dynamic and static superimposed loads are consistent, also, peak strength, fracture duration are linearly negatively correlated with pre-loading static, and logarithmically positively correlated with cyclic impact frequency. The maximum strain, fracture fractal dimension, and fragment fractal dimension are linearly positively correlated with pre-loading static, and logarithmically negatively correlated with cyclic impact frequency. Under different dynamic and static superpositions, the evolution trend of the fractal dimension of rock surface cracks and fragment sizes are basically consistent, and the former is larger than the latter, that shows the synchronicity of the development of rock surface and internal cracks, and rock surface cracks are more prone to generation and expansion. As the pre-loading static increases or the impact frequency decreases, the rock failure gradually intensifies, and the failure mode undergoes a transition from “inclined shear failure to vertical tensile failure to overall burst failure”. The burst failure position extends from bottom to overall. To quantify the damage mechanism of pre-loading static and cyclic impact, a dynamic static superimposed damage factor evolution model was established, which comprehensively considers static load damage, different peak, frequency, and number of cyclic impact damage, and strain rate strengthening effects. Further dynamic and static superposition experiments were conducted, and the error rates of rock peak strength obtained from theoretical calculations and experimental results were 0.5%, 1.8%, 0.6%, and 1.7%, respectively, the errors were relatively small. The theoretical calculation strength based on the superposition of dynamic and static damage factors is lower than the experimental strength. Preliminary analysis shows that this is due to the microscopic hysteresis of damage development under high-frequency cyclic impact. The actual cumulative damage generated by cyclic impact is less than single impact damage multiplied by cycle number. In the later stage, the microscopic testing can be carried out to explore the evolution law of rock microscopic damage under cyclic impact and further improve the theoretical model

Fine mapping and candidate gene analysis of proportion of four-seed pods by soybean CSSLs

Soybean yield, as one of the most important and consistent breeding goals, can be greatly affected by the proportion of four-seed pods (PoFSP). In this study, QTL mapping was performed by PoFSP data and BLUE (Best Linear Unbiased Estimator) value of the chromosome segment substitution line population (CSSLs) constructed previously by the laboratory from 2016 to 2018, and phenotype-based bulked segregant analysis (BSA) was performed using the plant lines with PoFSP extreme phenotype. Totally, 5 ICIM QTLs were repeatedly detected, and 6 BSA QTLs were identified in CSSLs. For QTL (qPoFSP13-1) repeated in ICIM and BSA results, the secondary segregation populations were constructed for fine mapping and the interval was reduced to 100Kb. The mapping results showed that the QTL had an additive effect of gain from wild parents. A total of 14 genes were annotated in the delimited interval by fine mapping. Sequence analysis showed that all 14 genes had genetic variation in promoter region or CDS region. The qRT−PCR results showed that a total of 5 candidate genes were differentially expressed between the plant lines having antagonistic extreme phenotype (High PoFSP > 35.92%, low PoFSP< 17.56%). The results of haplotype analysis showed that all five genes had two or more major haplotypes in the resource population. Significant analysis of phenotypic differences between major haplotypes showed all five candidate genes had haplotype differences. And the genotypes of the major haplotypes with relatively high PoFSP of each gene were similar to those of wild soybean. The results of this study were of great significance to the study of candidate genes affecting soybean PoFSP, and provided a basis for the study of molecular marker-assisted selection (MAS) breeding and four-seed pods domestication

Force and energy analysis of single-piston free-piston expander—linear generator

The movement of piston in free-piston expander-linear generator (FPE-LG) mainly depends on the dynamic force balance among four kinds of forces (air impetus, air resistance, electromagnetic resistance and frictional resistance). In this paper, the Newton's Second Law and the first law of thermodynamics are used to analyze the single-piston FPE-LG, the change of four kinds of forces and work produced by the four kinds of forces are analyzed. Nominal work-electricity conversion loss coefficient is proposed for the firs time to represent the energy loss. The experiment results show that the work produced by four forces from top dead center (TDC) to bottom dead center (BDC) are higher than those from BDC to TDC. The minimum proportion of air resistance energy consumption is also more than 50%, the proportion of electromagnetic resistance energy consumption is less than 20%, and the proportion of frictional resistance energy consumption is more than 20%. Therefore, the total nominal work-electricity conversion loss can be effectively reduced by increasing intake time or intake pressure.•Newton's Second Law is used to analyze the change of forces.•The first law of thermodynamics is used to analyze work produced by different forces.•Increasing intake time or intake pressure in a certain range can reduce energy loss