圆柱螺旋弹簧疲劳强度的可靠性设计

指出传统机械设计的缺陷,结合现代机械设计理论,并基于应力和强度干涉模型,介绍了圆柱螺旋弹簧疲劳强度的可靠性设计,同时利用实例,进一步阐明了设计步聚。对于重要或有可靠性要求的圆柱螺旋弹簧提供了可行的设计方法。

碟式离心机转鼓筒体的动态可靠性研究

以碟式离心机转鼓为研究对象,建立考虑载荷时间历程和结构参数同为随机性的结构动态可靠性模型,得到转鼓筒体的可靠度和失效率随时间变化规律。首先利用Lagrange方程,建立转鼓与分离物流固耦合关系的解析动力学模型;然后以有限元仿真计算软件为平台,施加流固耦合载荷,采用随机抽样,得到转鼓筒体应力分布的统计特性;最后应用随机过程和应力与强度干涉理论,给出结构动态可靠性的评估指标。结论表明:碟式离心机正常工况下,最大应力集中区发生在沉渣区部位,其等效应力呈现时变正态分布,连续工作2000 h后,转鼓筒体强度满足要求的概率低于80%,寿命符合“浴盆”曲线中早期失效的特征,这为高速碟式分离机的动态优化设计奠定了基础。

ANALYSIS OF STRESS FIELD NEAR CRACK TIP BASED ON ELECTRIC SATURATION MODEL

Within the framework of nonlinear eleetroelasticity, the stress field near to the crack tip in an infinite piezoelectric media subject to a far field uniform loading is studied by using an electrical strip saturation model and the complex variable method. And the emphasis is placed on the stress field near to the crack tip. The obtained solutions show that the normalized stress components at an arbitrary point near to the crack tip are determined by the angle of the point. Moreover, the stress components are independent of the distance from the point to the ori- gin of the coordinate. The distributions of in-plane stress components near to the crack tip are analyzed based on numerical results for PZT-SH. Compared with some related solutions, results show that the solutions are valid.

轻量化货箱设计

随着节能降耗要求的提高,车厢轻量化以及自洁性好成为矿用自卸车主要发展趋势。传统的自卸车货箱设计的边角存在死角,在卸货时容易粘箱,卸货不干净;自重较重,结构不够优化。应力集中比较明显。利用PROE对传统车厢进行分析发现弊端比较明显。基于此种情况在传统车厢的基础上开发出U型的结构。并利用PROE对其进行强度校核,观察其应力和强度情况。

Crack initiation stress and strain of jointed rock containing multi-cracks under uniaxial compressive loading: A particle flow code approach

The ratio of crack initiation stress to the uniaxial compressive strength(SCI,B/SUC,B) and the ratio of axial strain at the crack initiation stress to the axial strain at the uniaxial compressive strength(B,UCB,CI,A,A/SSSS) were studied by performing numerical stress analysis on blocks having multi flaws at close spacing's under uniaxial loading using PFC3 D. The following findings are obtained: SCI,B/SUC,B has an average value of about 0.5 with a variability of ± 0.1. This range agrees quite well with the values obtained by former research. For joint inclination angle, β=90°,B,UCB,CI,A,A/SSSS is found to be around 0.48 irrespective of the value of joint continuity factor, k. No particular relation is found betweenB,UCB,CI,A,A/SSSS and β; however, the average B,UCB,CI,A,A/SSSS seems to slightly decrease with increasing k. The variability ofB,UCB,CI,A,A/SSSS is found to increase with k.Based on the cases studied in this work,B,UCB,CI,A,A/SSSS ranges between 0.3 and 0.5. This range is quite close to the range of 0.4to 0.6 obtained for SCI,B/SUC,B. The highest variability of ± 0.12 forB,UCB,CI,A,A/SSSS is obtained for k=0.8. For the remaining k values the variability ofB,UCB,CI,A,A/SSSS can be expressed within ± 0.05. This finding is very similar to the finding obtained for the variability of SCI,B/SUC,B.

Finite element analysis of road structure containing top-down crack within asphalt concrete layer

In this paper, a four-layered road structure containing a top-down crack is investigated by performing finite element analyses in ABAQUS. In this study, in addition to the vertical load of a vehicle wheel, the horizontal load as well as its position with respect to the crack is also considered in the analyses, and the crack tip parameters including stress intensity factors(SIFs) and T-stress are then calculated. Moreover, influence of elastic modulus and thickness of the pavement layers on the crack tip parameters is studied. Results show that the horizontal and vertical loads along with their position with respect to the crack, elastic modulus and thickness of the road layers influence the crack tip parameters(KⅠ, KⅡ and T-stress) significantly. It was also found that for the cases that the vehicle wheel is positioned near the crack plane, only the shear deformation mode is observed at the crack tip;while, for the vehicle wheel positions far from the crack, only the opening mode is observed, and between these positions, both the opening and shear deformation modes(i.e., mixed mode Ⅰ/Ⅱ) are observed at the crack tip.

论地震发生机制

地震发生的物理机制和过程是还没有认识清楚的问题.此前人们将浅源地震归因于弹性回跳,根据这一观点和岩石实验结果计算得到的地震能量与实际观测结果有很大矛盾,被称之为"热流佯谬".中源和深源地震发生在地幔区域,其成因也没有合理的解释.考虑到地壳和地幔是离散集合态物质体系及其慢动力学运动行为的基本特点,本文根据物理学原理,特别是近年凝聚态物理发展出来的相关新观念,并依据已有观测事实,从新的视角探究地震发生的物理机制.1)关于地壳岩石层中的应力分布:在不考虑构造力时,依据万物皆流的流变学原理,原始地壳岩石在自重压强长时间作用下,纵向和横向应力相同,没有差应力.大地构造力推动岩块滞滑移动挤压断层泥,施加于其他岩块,逐渐传递和积累.这种附加的横向构造力与原始岩石中应力叠加,形成地壳岩石层中的实时应力.由于断层泥属于颗粒物质体系,具有与岩石不同的力学特征,其弹性模量比岩石小得多,且随压强而增大,导致构造作用力随深度非线性增大.给出了地壳中构造应力分布及其变化规律.2)关于地壳岩石层强度:地壳岩石的自重会使岩石发生弹性—塑性转变.通过对弹性—塑性转变深度的计算,并根据实际情况分析,给出了地壳岩石弹性、部分塑性和完全塑性三个区域的典型深度范围.在部分塑性区,塑性体比例达到约10%以上时,发生塑性连通,这时岩石剪切强度由塑性特征决定.塑性滑移的等效摩擦系数比脆性破裂小一个数量级以上,致使塑性滑移时岩石剪切强度比脆性破裂小得多.同时,随深度增大,有多种因素使得岩石剪切屈服强度减小.另一方面,地震是大范围岩石破坏,破坏必然沿薄弱路径发生.因此,浅源地震岩石的实际破坏强度必定比通常观测到的岩石剪切强度值低.给出了地壳岩石平均强度和实际破坏强度典型值随深度的分布规律.3)关于地震发生的条件和机制:地震发生必定产生体积膨胀,只有突破阻挡才可膨胀.地震发生的条件是:大地构造力超过岩石破坏强度、断层边界摩擦力以及所受阻挡力之和.因此,浅源地震是岩石突破阻挡发生的塑性滑移.在此基础上提出了浅源地震发生的四种可能模式.深源地震是冲破阻挡发生的大范围岩块流.浅源地震和深源地震都是堵塞—解堵塞转变,是解堵塞后岩石层块滑移或流动造成的能量释放.4)关于地震能量和临震前兆信息:地震能量即为堵塞—解堵塞转变过程释放的动能.以实例估算表明,地震岩石滑移动能与使岩块剪切破坏和克服周围摩擦阻力所需做的功相一致,不会出现热流佯谬.同时指出,通过观测地震发生前构造力的积累过程、局域地区地质变迁以及岩石状态变化等所产生的效应,均可能获得有价值的地震前兆信息.

From monoscale to multiscale modeling of fatigue crack growth:Stress and energy density factor

The formalism of the earlier fatigue crack growth models is retained to account for multiscaling of the fatigue process that involves the creation of macrocracks from the accumulation of micro damage.The effects of at least two scales,say micro to macro,must be accounted for.The same data can thus be reinterpreted by the invariancy of the transitional stress intensity factors such that the microcracking and macrocracking data would lie on a straight line.The threshold associated with the sigmoid curve disappears.Scale segmentation is shown to be a necessity for addressing multiscale energy dissipative processes such as fatigue and creep.Path independency and energy release rate are monoscale criteria that can lead to unphysical results,violating the first principles.Application of monoscale failure or fracture criteria to nanomaterials is taking toll at the expense of manufacturing super strength and light materials and structural components.This brief view is offered in the spirit of much needed additional research for the reinforcement of materials by creating nanoscale interfaces with sustainable time in service.The step by step consideraton at the different scales may offer a better understanding of the test data and their limitations with reference to space and time.

Large magnetocaloric effect in metamagnetic HoPdAl

Magnetic properties and magnetocaloric effects （MCEs） of the HoPdA1 compounds with the hexagonal ZrNiAl-type and the orthorhombic TiNiSi-type structures are investigated. Both the compounds are found to be antiferromagnet with the Nrel tem- perature TN=12 and 10 K, respectively. A field-induced metamagnetic transition from antiferromagnetic （AFM） state to ferro- magnetic （FM） state is observed below TN. For the hexagonal HoPdA1, a small magnetic field can induce an FM-like state due to a weak AFM coupling, which leads to a high saturation magnetization and gives rise to a large MCE around TN. The maxi- mal value of magnetic entropy change （ASM） is -20.6 J/kg K with a refrigerant capacity （RC） value of 386 J/kg for a field change of 0-5 T. For the orthorhombic HoPdA1, the critical field required for metamagnetic transition is estimated to be about 1.5 T, showing a strong AFM coupling. However, the maximal ASM value is still -13.7 J/kg K around TN for a field change of 0-5 T. The large reversible ASM and considerable RC suggest that HoPdA1 may be an appropriate candidate for magnetic re- frigerant in a low temperature range.