Experimental investigation of the failure mechanism of P110SS casing under opposed line load

Many studies focused on casing collapse strength under uniform load have been done, and the API 5C3 and ISO standards have been formed. However, only a limited number of researches on collapse failure mechanism of casing have been done under non-uniform load, especially experimental study, although the non-uniform load has a great impact on casing collapse strength. Hence, the collapse experiment is conducted for P110SS casing under opposed line load by using electro hydraulic servo pressure testing machine. The displacement variation rules of P110SS casing have been obtained under opposed line load. The strain of casing is measured in the process of collapse testing by the method of gluing strain-gauge on the outside surface of P110SS casing. The initial yield load of casing, instability load of casing and the yield load, stress-hardening rate, strain-hardening rate of casing after hardening are obtained. The stress-strain rules of casing after hardening are analyzed. The hardening characteristic and collapse failure mechanism of P110SS casing have been clarified under non-uniform load (under opposed line load). Experimental results can provide important references for the theoretical study on failure mechanism and collapse strength of casing under non-uniform load.     

Experimental study on the fatigue failure mechanism of QP-16 type ball-eye under asymmetric load

The ball eye (BE) is a key connecting component between the insulator and transmission tower, whose fatigue characteristics concern the safety of transmission lines. To understand the fatigue mechanism and characteristics of it, the fatigue test was conducted based on the following data: r = 0.25, S = 500 MPa,then plotting of SN and Δε_axis − N, to analyze the fatigue failure of the test specimen from the macro and micro point of views. The research results show that: the life of BE significantly reduces with the increase of the stress amplitude, but the relative reduction in life is not the same; softening and strain amplitude of the specimen change differently before and after the stress amplitude of 300 MPa; when S ≤ 300 MPa, the fracture is more smooth, the fatigue crack propagation is slow; when S > 300 MPa, the rate of fatigue crack growth is faster, and the fatigue crack growth zones are not obvious. The cracks are easily detectable appear at the joint of the BE and insulator cap, and the cracks along the fracture cross section are constantly expanding, showing multiple fatigue sources and fatigue steps. The number of fatigue steps increases as the magnitude of the tensile stress increases. When S = 500 MPa, the yield strength decreases during the lifetime, the decrease rate of the tensile strength and microstructure strength in each stage are different. Axial lengthening and section shrinkage ratio decrease with the development of fatigue, fatigue evolution process is accompanied by phenomenon of crystalline slip, deformation, dislocation, at the same time, dissipation and decomposition of pearlite occur, and carbide precipitates from the matrix, growing and moving to the grain boundaries, the specific phenomenon of grain growth appears.     

胶结充填体在动荷载作用下的响应特征

为掌握大红山铜矿井下在用的胶结充填材料对爆破荷载的响应特征,对质量浓度为72%、水泥含量为180 kg/m³的胶结充填材料开展了不同加载应变率下的常规单轴冲击试验。试验结果表明:CTB_(180)试件对入射冲击波的透射能力微弱,在较低的冲击应变率作用下即发生破裂;当■_s≥42.3 s3的胶结充填材料开展了不同加载应变率下的常规单轴冲击试验。试验结果表明:CTB_(180)试件对入射冲击波的透射能力微弱,在较低的冲击应变率作用下即发生破裂;当■_s≥42.3 s^(-1)时,试件韧性增加,试件瞬间被压密,增幅较■_s=30.3 s(-1)时,试件韧性增加,试件瞬间被压密,增幅较■_s=30.3 s^(-1)时明显提升,破坏应变量发生了突增;随着■_s的增加,反射能占比先减后增,透射能占比先增后减,但耗散能占比呈递增趋势;破坏形态上,当■_s≤20.7 s(-1)时明显提升,破坏应变量发生了突增;随着■_s的增加,反射能占比先减后增,透射能占比先增后减,但耗散能占比呈递增趋势;破坏形态上,当■_s≤20.7 s^(-1)时,试件仍保持其整体性,但当■_s≥42.3 s(-1)时,试件仍保持其整体性,但当■_s≥42.3 s^(-1)时,将整体失稳破坏。研究结果可以指导充填材料配比选型以及矿柱回采爆破参数优化。     

动载下胶结充填体的力学特性试验研究

胶结充填体的稳定性对于矿山安全生产至关重要。为了研究动载作用下充填体的动力学特性,利用霍普金森压杆(SHPB)对充填体进行单轴冲击试验,研究充填体应力应变曲线、动态抗压强度、动态强度增长因子与平均应变率之间的关系。结果表明,当平均应变率低于60 s^(-1)时,应力应变曲线峰后阶段为"应变回弹"类型;超过80 s(-1)时,应力应变曲线峰后阶段为"应变回弹"类型;超过80 s^(-1)时,为"峰后塑性"类型;介于二者之间时,为"应力跌落"类型;随着平均应变率的增大,试样动态抗压强度先迅速增大,后趋于稳定,对应的平均应变率临界值为80 s(-1)时,为"峰后塑性"类型;介于二者之间时,为"应力跌落"类型;随着平均应变率的增大,试样动态抗压强度先迅速增大,后趋于稳定,对应的平均应变率临界值为80 s^(-1)。利用Gompertz模型能较好的描述充填体动态抗压强度与平均应变率之间的关系;动态强度增长因子与平均应变率正相关,当平均应变率处于40～130 s(-1)。利用Gompertz模型能较好的描述充填体动态抗压强度与平均应变率之间的关系;动态强度增长因子与平均应变率正相关,当平均应变率处于40～130 s^(-1),动态强度增长因子范围在1.5～3之间。     

复合材料机身曲板环向弯曲加载试验及失效机制

对复合材料机身曲板进行了环向弯曲加载试验,采用四点弯加载方式对考核段进行纯弯加载,设计一种加强连接方式避免加载段提前破坏,通过试验对机身曲板的环向稳定性和破坏模式进行了分析。同时,建立了基于内聚力单元的考虑长桁与蒙皮粘接界面损伤的有限元模型,分别使用Quads准则和Hashin准则作为界面和层合板的失效判据分析曲板结构的失效机制,计算结果与试验结果吻合较好。试验及有限元分析结果表明,长桁帽底蒙皮的局部屈曲引起长桁与蒙皮粘接的R区出现初始开裂,并最终扩展为长桁脱粘。随着蒙皮屈曲及长桁脱粘的扩大,蒙皮由局部屈曲变为整体失稳而失去承载能力,最终导致隔框承载过大而发生断裂。根据初始损伤模式,采取了长桁帽内全包工艺改进设计,改进后的曲板结构稳定性和承载能力分别提高了21.9%和16.8%。      

Dilatometric study of the sintering mechanism of nanocrystalline cemented carbides

Two types of WC-Co powders, nanometer particle size and micron particle size, were studied by means of dilatometry. The experiments showed that the sintering behavior of the nanocrystalline specimens is different from that of the micron grain-size specimen. While the sintering of the micron particle sized powder to full density is mainly done in the liquid phase, the nanoparticle sized powder can be sintered in the solid phase, at a lower temperature.     

平面钢框架在撞击荷载作用下的抗连续倒塌分析

各种自然灾害和人为因素都可能造成结构连续倒塌,抗连续倒塌研究经常抛开引起倒塌破坏的原因,直接拆除关键柱,研究剩余结构的抗倒塌性能.该研究以平面框架受撞击荷载为例分析具体灾害对框架结构抗倒塌性能的影响,提出一种撞击力简化模型,分析结构体系对撞击力的激励反应,并将撞击拆柱法模拟结果与传统直接拆柱法结果对比,分析两种方法对结...     

Vibrations of non-uniform functionally graded MWCNTs-polystyrene nanocomposite beams under action of moving load

Free and forced vibrations of non-uniform functionally graded multi-walled carbon nanotubes (MWCNTs)-polystyrene nanocomposite beams are investigated via Timoshenko beam theory. Different MWCNTs distributions in the thickness direction are introduced to improve fundamental natural frequency and dynamic behavior of non-uniform polymer composite beam under action of moving load. So, linear distribution patterns of carbon nanotubes (CNTs) in the thickness direction which can readily be achieved in practice are studied. The effects of shear deformation, rotary inertia, non-uniformity of the cross-section are also considered in the formulation. The finite element method is employed to obtain a numerical approximation of the motion equation. The non-uniform beam is approximated by another beam consisting of n elements with piecewise constant thickness so that the volume remains constant for each element. The effects of non-uniformity parameters, material distributions, velocity of the moving load and boundary conditions on the dynamic behavior are investigated. It is found that the symmetrical linear distribution of MWCNTs results in an increase in the fundamental natural frequency of nanocomposite beams which are higher than those of beams with uniform and unsymmetrical MWCNTs distributions.     

剪切载荷作用下复合材料挖补修理层合板试验及有限元分析

为了确定剪切载荷作用下含非穿透损伤复合材料挖补修理层合板的破坏模式和抗剪切能力,进行了复合材料挖补修理层合板的剪切试验,并与未损伤复合材料层合板进行对比。试验结果表明,复合材料挖补修理后的层合板具有较高的强度恢复率,且不影响层合板的后屈曲承载能力。同时,建立了剪切载荷作用下复合材料挖补修理层合板的有限元分析（FEA）模型,复合材料母板和补片采用了三维Hashin准则来判定材料失效,母板层与层之间采用零厚度界面单元以有效模拟剪切载荷作用下复合材料母板上、下子板之间的分层。该模型得到的破坏模式与试验结果基本相符。由于挖补修理的设计与工艺复杂性,理论模拟的破坏载荷与试验结果虽不能完全吻合,但其最大15%左右的差异能够满足修理设计的需要。以上结果说明,该模型对剪切载荷作用下复合材料挖补修理层合板的破坏模式和破坏载荷能够进行工程适用的预测。     

Experimental and FEM failure analysis and optimization of a centrifugal-pump volute casing

Material and geometry are two key factors in ideal mechanical performance of centrifugal-pump casings engaged in high pressures.This paper presents the model generation, static structural analysis, and geometrical modifications performed for a failed volute casing of a real centrifugal-pump. Failure would be examined under hydrostatic test conditions. Finite Element Method is employed in stage of theoretical problem investigation.To control failure phenomenon, necessary geometrical modifications are applied to the model. Geometrical modifications must have the least effect on hydraulic performance and avoid excessive manufacturing costs.Finally, some test volute casings with new geometry would be built to experimentally validate the analytical results and inspect the hydraulic performance.     

混凝土冻融循环下动态破损机理的试验研究

对冻融环境下混凝土试样进行了不同加载速率下的单轴压缩试验,得到了混凝土材料经历不同冻融循环次数下的质量损失及破损形态,分析了冻融循环下混凝土试样的全应力—应变曲线,并给出了其单轴极限抗压强度、峰值应变随加载速率的变化特征。通过运用CT细观试验的方法初步对经历不同加载速率下的试样进行了细观结构分析。试验结果表明:在相同加载率下,混凝土单轴动态极限抗压强度随冻融循环次数的增加而降低;在相同冻融循环次数下,混凝土单轴动态极限抗压强度随加载速率的增大而提高;冻融循环作用下,在低加载速率下,混凝土试样破坏时,裂纹数目较少,主要沿砂浆和交界面处扩展,破坏时呈现出集中式的分布;而在高加载速率下,裂纹逐渐变得分散,破坏时呈现弥散状分布式的裂纹,随着加载率的提高,裂纹穿过骨料的现象增多,骨料破坏数目呈指数形式增长。以此,通过试验系统地研究了冻融循环下混凝土动态破损机理。     

Experimental study of dissolution kinetics of divided non-uniform grained solids

Usually, dissolution studies of soluble powders do not take into account the existence of the size distribution of particles. It is shown that this concept is of fundamental interest in the prevision of particular aspects of the dissolution process, like the total time required for complete dissolution. The study of the evolution of grain size distribution was carried out with a laser beam scattering sizer. A numerical simulation was set up based on the results obtained.     

含冲击损伤复合材料层压板压缩破坏机制试验研究

为了研究含冲击损伤复合材料层压板的压缩破坏机制, 通过前后表面超声C扫描获得分层损伤在层压板内的分布情况, 使用应变片获取层压板两面的应变场, 采用声发射观察层压板压缩破坏过程。研究发现: 冲击分层损伤在厚度方向上的非对称分布引起层压板内部出现严重的应力集中, 致使纤维断裂并最终导致层压板整体破坏; 导致含冲击损伤层压板压缩破坏的主要原因为纤维断裂而非分层扩展。     

爆炸载荷作用下多层介质破坏的影响因素

针对现代战场上对多层介质破坏难的问题,提出多层介质结构模型来研究多层介质的破坏机理。通过理论分析、数值模拟及试验方法研究了介质性质、起爆方式、炸深对多层介质破坏的影响。结果表明:介质波阻抗越接近,能量传递利用率越高;下端起爆方式更有利于多层介质破坏作用;多层介质存在一个最佳炸深。研究结果对提高多层介质目标破坏作用有一定指导意义。     

爆炸载荷作用下多层介质破坏的影响因素

针对现代战场上对多层介质破坏难的问题,提出多层介质结构模型来研究多层介质的破坏机理。通过理论分析、数值模拟及试验方法研究了介质性质、起爆方式、炸深对多层介质破坏的影响。结果表明:介质波阻抗越接近,能量传递利用率越高;下端起爆方式更有利于多层介质破坏作用;多层介质存在一个最佳炸深。研究结果对提高多层介质目标破坏作用有一定指导意义。     

剪切载荷下含椭圆形大开口层合板的试验研究

在面内纯剪切载荷作用下, 采用试验与有限元模拟方法研究了结构中心设置椭圆形大开口的正方形复合材料层合板的应力/应变集中现象及屈曲、 后屈曲行为, 通过测试结果对试验件失效模式进行了评估。研究结果表明: 层合板开口附近应力/应变集中程度很高; 大尺寸开口使结构稳定性显著降低, 且开口层合板具有较好的后屈曲承载能力; 由于弯曲产生高水平的层间应力, 导致局部分层损伤并伴有基纤剪切破坏; 随着横向挠度的增加, 各应力集中区域的纤维发生拉伸断裂, 导致整体结构瞬间发生脆性失效。有限元模拟结果与试验结果符合较好。     

Experimental study on the compression properties and failure mechanism of 3D integrated woven spacer composites

The compressive experiments on the 3D integrated woven spacer composites with different core heights are performed in the flat and warp direction. Macro-fracture morphology and SEM micrographs have been examined to understand the deformation and failure mechanism. The results show that the core height is an important parameter to influence the compressive properties and failure mechanism. For flat compression, the compressive properties decrease with the core height and load–displacement curves exhibit elastic, plasticity plateau and densification stages. For high core height, yet more than one peak load appears. For warp compression, the compressive properties increase greatly with the core height and the curves only have obvious elastic stage. Meanwhile, the failure mechanism is significantly different under the flat and warp compression. For flat compression, core fiber bundles dominate the failure and three typical failure mechanisms have been obtained for different core heights. For warp compression, it is the face sheet rupture and dislocation between the top and bottom face sheets that dominate the failure of the composites.