MRI对半月板隐形层裂的诊断

目的:探讨MRI对半月板隐形层裂的诊断价值。方法:对15例半月板隐形层裂患者的MRI图像与关节镜检术手术录像进行回顾性分析和对比。结果:15例患者根据MRI分级,其中Ⅰ级4例,Ⅱ级11例。经关节镜检术后疗效好。结论:膝关节MRI检查能够准确地提供半月板撕裂部位、形态,对关节镜检术有指导意义。

半月板隐性层裂的MRI检查对行关节镜检术的意义

目的通过半月板隐性层裂的MRI和关节镜下征象的对比研究,明确术前MRI检查的重要性,并探讨其关节镜治疗方法。方法对17例半月板隐性层裂的MRI表现和镜下所见进行回顾性分析。结果本组镜下未见半月板层裂,而术前MRI检查证实有半月板层裂现象。结论术前MRI检查对于症状及体征不典型的半月板隐性层裂的诊断及治疗方式具有指导性意义,而仅凭关节镜检查,直视下难以确诊此类病变。

巷道煤壁在地应力作用下失稳特征的试验研究

煤矿围岩体失稳动力灾害现象主要表现之一就是冲击矿压。根据煤岩试样受载情况设计了加载装置,利用MTS815.02岩石力学试验系统及多点动态数据采集系统,对巷道煤壁附近围岩体劈裂成板、失稳破断及突出的全过程进行了试验研究,结果表明:煤壁自由面侧向变形随层裂板的弯曲逐渐增大,并在煤块弹射时突然减小;地应力导致煤壁内裂隙主要沿铅垂方向扩展,形成板结构,并向煤岩内部逐步发展、破坏;煤壁失稳分为层裂板的形成、屈曲失稳并剥离、大范围崩裂突出三个阶段,其中后两个阶段发生时间极短。

Formability of aluminum-silicon coated boron steel in hot stamping process

Flow behavior of the Al-Si coated boron steel was investigated with Gleeble-3500,in comparison with the uncoated one.Effect of deformation conditions on the coating integrity was characterized by optical microscopy.Facture surfaces of the coated steels were inspected under SEM.Experimental results indicate that the ultimate tensile strength and ductility of the Al-Si coated boron steel are lower than those of the uncoated steel under test conditions.Extensive cracks occur in the coating after tensile tests;the width and density of cracks are sensitive to the deformation temperatures and strain rates.The bare substrate exposed between the separate coating segments is oxidized.Appearance of the oxide degrades the Al-Si coating adhesion.Remarkable difference between formability of the coating layer and the substrate is confirmed.The formability of the Al-Si coating could be optimized by controlling the phase transformation of the ductile Fe-rich intermetallic compounds within it during the austenization.

INTERLAMINAR FRACTURE TOUGHNESS OF MULTI-DIRECTIONAL LAMINATES

Based on the conventional compliance and area methods, a high precision method named the angle method is presented in this work. The interlaminar fracture toughness is determined by measurement of the load and the bending angle at the loading point without measurement of the crack length, and the improvement of the conventional compliance method is made, which is more precise and can be used to general DCB specimen with unequal flexural stiffness of the cantilevers. The interlaminar fracture toughness in 0/ θ(θ =0°,30°,60°,90°) interfaces of two epoxy composites, one being the carbon fibre reinforced brittle matrix T300/4211, the other the carbon fibre reinforced tough matrix T300/3261, is measured by both compliance and angle methods, and the relationship between fracture toughness and the ply angle θ is obtained. It is found that the interlaminar fracture toughness is correlated with the type of matrix and the ply angles near the crack front.

A METHOD FOR PREDICTING BUCKLING LOADS OF COMPOSITE LAMINATED STRIPS WITH A SURFACE NOTCH

Surface notches lower the stiffness of laminated strips, so they lower the buckling loads of the laminated strips, too. In this paper a new method is proposed to predict the buckling loads of the laminated strips with a surface notch. The theoretical and experimental results show that the buckling loads decrease as the depth or width of the surface notches increase; when the stacking sequence of the laminated strips is [0°/0°/+ θ/-θ/0°/0°/+θ/-θ] s , the buckling load decrease as θ increases. It proves that the method is reliable and significant.

Influence of lateral pressure on mechanical behavior of different rock types under biaxial compression

Lots of field investigations have proven that layer-crack structure usually appears during the excavation process of deep rock or coal mass.To provide experimental data for studying the formation mechanism of layer-crack structure,this study researches the influence of lateral pressure on the mechanical behavior of different rock types.Four rock types have been tested and the formation mechanism of macro-fracture surface is analyzed.Results indicate that the brittleness and burst proneness of rock or coal material are stronger than that of gypsum material due to the different mineral compositions and structures.When the lateral pressure is less than 10%uniaxial strength,the peak stress and elastic modulus increase with the increase of lateral pressure;but when the lateral pressure is larger than 10%uniaxial strength,the two parameters decrease slightly or keep steady.This is because when the lateral pressure reaches a certain value,local failure will be formed during the process of applying lateral pressure.Under the condition of low lateral pressure,the failure of the specimen is dominated by the tensile mechanism;under the condition of relatively high lateral pressure,the area of the specimen close to the free surface is tensile splitting failure,and the area far from the free surface is shear failure.

Study on first caving fracture mechanism of overlying roof rock in steep thick coal seam

Based on the elastic plate theory, a mechanical model of thin plate for the first caving of overlying roof rock in steep mining face was established. The analytical solution of the deflection and stress distribution of roof rocks was obtained. According to the specific geological conditions of the 5-103 panel in Shanxi,the failure of roof rocks and the influence of seam dip on it during the exploitation were theoretically investigated. Meanwhile, the first caving characteristics of the overlying rock in the steep coal seam were investigated based on its stress contour. The results show that the dip angle has a distinct influence on the caving interval and the first caving interval for the 5-103 panel is 37 m in theory. Finally, a systematic monitoring on the behavior of rock pressures was conducted. The measured results agree well with the theoretical prediction, which provides a good reference for practical steep coal seam mining.

Experimental and finite element analysis for fracture of coating layer of galvannealed steel sheet

Mechanical properties of galvannealed (GA) steel sheet used for automotive exposed panel and predicted failure phenomenon of its coating layer were evaluated using finite element method. V-bending test was performed to understand better the fracture of coating layer of GA steel sheet during plastic deformation. Yield strength of the coating layer was calculated by using a relative difference between hardness of coating layer measured from the nano-indentation test and that of substrate. To measure shearing strength at the interface between substrate and coating layer, shearing test with two specimens attached by an adhesive was carried out. Using the mechanical properties measured, a series of finite element analyses coupled with a failure model was performed. Results reveal that the fracture of coating layer occurs in an irregular manner at the region where compressive deformation is dominant. Meanwhile, a series of vertical cracks perpendicular to material surface are observed at the tensile stressed-region. It is found that 0.26-0.28 of local equivalent plastic strain exists at the coating and substrate at the beginning of failure. The fracture of coating layer depends on ductility of the coating layer considerably as well.

DNS study on bursting and intermittency in late boundary layer transition

Experimental and numerical investigations have suggested the existence of a strong correlation between the passage of coherent structures and events of bursting and intermittency. However, a detailed cause-and-effect study on the subject is rarely found in the literature due to the complexity and the nonlinear multiscale nature of turbulent flows. The primary goal of this research is to explore the motion and evolution of coherent structures during late transition, whose structure is much more ordered than that of fully developed turbulence, and their relationship with events of bursting and intermittency based on a verified high-order direct numerical simulation(DNS). The computation was carried out on a flat plate at Reynolds number 1000(based on the inflow displacement thickness) with an inflow Mach number 0.5. It is concluded that bursting and intermittency detected by stationary sensors in a transitional boundary layer actually result from the passage and development of vortical structures, and it would be more rational to design transitional turbulence models based on modelling the moving vortical structures rather than the statistical features and experimental experiences.