NONSMOOTH MODEL FOR PLASTIC LIMIT ANALYSIS AND ITS SMOOTHING ALGORITHM

By means of Lagrange duality of Hill＇s maximum plastic work principle theory of the convex program, a dual problem under Mises＇ yield condition has been derived and whereby a non-differentiable convex optimization model for the limit analysis is developed. With this model, it is not necessary to linearize the yield condition and its discrete form becomes a minimization problem of the sum of Euclidean norms subject to linear constraints. Aimed at resolving the non-differentiability of Euclidean norms, a smoothing algorithm for the limit analysis of perfect-plastic continuum media is proposed. Its efficiency is demonstrated by computing the limit load factor and the collapse state for some plane stress and plain strain problems.

PLASTIC LIMIT ANALYSIS OF INCOMPATIBLE FINITE ELEMENT METHOD

This paper describes an incompatible finite element model satisfying the consistency condition of energy to solve the numerical precision problem of finite element solution in perfectly plastic analysis. In this paper the reason and criterion of the application of the model to plastic limit analysis are discussed, and an algorithm of computing plastic limit load is given.

PLASTIC LIMIT ANALYSIS OF DISCONTINUOUS LINING UNDERGROUND PRESSURE

Discontinuous lining is a special form of support in underground excavation. Based on the method of plastic limit analysis, it is found the upper and the lower bound solution of the pressure of circular discontinuous lining and discussed support parameter of discontinuous lining and its applicable conditions , which provides theoretical basis for the design and calculation of discontinuous lining.

Plastic limit load analysis for pressure pipe with incomplete welding defects based on the extended Net Section Collapse Criteria

With von Mises yield criterion,the loading range of Net Section Collapse(NSC) Criteria is extended from combined tension and bending loadings to combined bending,torsion and internal pressure loadings.A new theoretical analyzing method of plastic limit load for pressure pipe with incomplete welding defects based on the extended NSC Criteria is presented and the correlative formulas are deduced,the influences of pipe curvature,circumferential length and depth of incomplete welding defects on the plastic limit load of pressure pipe are considered as well in this method.Meanwhile,according to the orthogonal experimental design method,the plastic limit loads are calculated by the finite element method and compared with the theoretical values.The results show that the expressions of plastic limit load of pressure pipe with incomplete welding defects under bending,torsion and internal pressure based on extended NSC criteria are reliable.The study provides an important theoretical basis for the establishment of safety assessment measure towards pressure pipe with incomplete welding defects.

Mesenchymal Stem Cells Express Low Levels of Cardiomyogenic Genes and Show Limited Plasticity towards Cardiomyogenic Phenotype

Mesenchymal stem cell differentiation towards osteogenic, chondrogenic and adipogenic lineages have been extensively described and reproduced in the literature. In contrast, cardiomyogenic differentiation still remains largely controversial. In this study the authors aim to shed new light into this unclear phenomenon and test whether BMMSC （bone marrow mesenchymal stem cells） and ATMSC （adipose tissue derived mesenchymal stem cells） are able to differentiate into functional cardiomyocytes, investigating two differentiation protocols. AT and BMMSC behaved differently when cultured in differentiation media and presented lower levels of proliferation and alkaline phosphatase production, expression of cardiomyocyte-specific transcription factors such as GATA-4, Nkx2-5 and proteins such as ct and 13 Myosin Heavy Chains. Furthermore, MSC started to express higher levels of Connexin-43 and c~ sarcomeric actinin protein. Unfortunately, though, MSC did not present cardiomyocyte-like electrophysiological properties. In order to analyze a possible explanation for such limited plasticity, the authors decided to address the issue using a quantitative approach. Gene expression was quantified by Real time PCR, and, for the first time, the authors show that a possible explanation for limited plasticity of MSC is that even though differentiated cells presented differential gene expression, the levels of key cardiomyogenic genes did not reach expression levels presented by adult cardiomyocytes, nor were maintained along differentiation, reaching peaks at 4 days of stimulation, and decaying thereafter.

崩岗土壤液塑限的离子特异性效应

为探究崩岗土壤液塑限的离子特异性效应,选取福建省长汀县河田镇一处稳定型崩岗的3个土层土壤(红土层、砂土层和碎屑层)为研究对象,用液塑限联合测定仪对不同离子(Li^(+)、Na^(+)和K^(+))盐溶液交换处理后的土壤液塑限进行分析。结果表明,红土层的土壤塑限、液限和塑性指数均显著高于砂土层和碎屑层(P<0.05)。土壤塑限和液限均与土壤黏粒含量、有机质含量、阳离子交换量以及高岭石含量呈正相关关系,其中,土壤塑限与黏粒含量和阳离子交换量呈显著正相关关系(P<0.05)。K^(+)交换处理后,红土层土壤塑限、液限和塑性指数比Li^(+)交换处理分别高5.80%、9.53%和12.99%,比Na^(+)交换处理分别高3.50%、9.77%和15.86%;K^(+)交换处理后,砂土层土壤塑限、液限和塑性指数比Li^(+)交换处理分别高7.22%、6.69%和6.83%,比Na^(+)交换处理分别高4.33%、5.27%和7.32%;而不同离子对碎屑层土壤液塑限的影响不显著。不同离子对同一土层土壤液塑限的影响不同,K^(+)交换处理后红土层、砂土层的土壤液塑限总体高于Li^(+)和Na^(+)交换处理,即较Li^(+)和Na^(+)而言,K^(+)可提高崩岗土壤液塑限。

压力容器及容器-管道系统的安定载荷计算方法对比

针对压力容器及容器-管道系统的安定载荷计算,介绍了循环弹塑性分析法、下限安定定理法和双极限载荷法3种求解安定载荷方法的原理和流程。基于这3种方法,具体计算了机械载荷下厚壁圆筒和标准椭圆封头中心接管的安定载荷,以及热载荷下标准椭圆封头中心管系整体模型的安定载荷,并对比分析了3种方法的优缺点。结果表明,循环弹塑性分析法能较准确地反映结构的实际承载能力,但求解复杂、工作量最大;双极限载荷法和下限安定定理法相对于循环弹塑性分析法的最大误差均小于5%,且偏保守,双极限载荷法的计算量最小。综合考虑计算精度和工作量,在工程设计中可采用双极限载荷法;对于计算精度要求较高、周围弹性材料对最大应力点的约束能力较弱的情况,建议采用循环弹塑性分析法。

冲击性煤体应力结构时间效应试验研究

煤矿工程中蕴含复杂的应力结构时间效应问题,与冲击地压灾害的发生与防治密切相关。针对冲击性煤体的应力结构时间效应开展试验研究,在陕西、甘肃以及内蒙古3个冲击地压矿井取得煤岩块体加工试件,通过煤单轴压缩动静载及蠕变试验研究加载速率的应力时间效应,采取长时分段试验方法研究煤原位解除条件下的应力时间效应,开展煤浸水以及煤岩组合试验研究结构时间效应。结果表明:煤体单轴抗压强度与加载速率具有正相关性,与原位解除时长和浸水时间具有负相关性,煤岩结构时间效应下的组合模式对其能量及强度属性有显著影响,冲击性煤体表现出应力与结构2个方面的时间效应。依据试验结果,提出塑限结构来解释应力作用下煤岩体的不可逆变形,再通过构建塑限结构时间效应模型,对比非弹性应变与不可逆应变的数值近似性,对冲击性煤体塑限应变特性进行了验证。

“限塑令”背景下可降解塑料吸管产品质量状况研究

“限塑令”背景下可降解吸管需求旺盛,了解其产品质量状况尤为重要。本文浅析了当前降解吸管发展状况和相关标准,从流通领域和电商平台采集了10组降解吸管,进行了生物降解试验,发现2组不合格产品,通过热重和红外光谱分析,确定不合格样品是以聚丙烯为主要原料的吸管。针对降解吸管提出了监管和使用的建议。

富里酸对红黏土液塑限的影响及其微观机制

通过在红黏土中掺入不同含量的富里酸粉末和蒸馏水制样,并设计不同的浸泡时间,探讨了富里酸对红黏土液塑限的影响规律。试验结果表明,富里酸呈弱酸性,能够溶解土体矿物成分;浸泡时间一定后,土体液限随富里酸粉末与红黏土质量比的增加而减小,塑限先减小后增大;富里酸粉末与红黏土质量比一定时,土体液限随浸泡时间的增加先减小后增大,塑限先增大后减小。

硅酸钾溶液对黏性土体微观结构的影响研究

为更好满足工程中的要求,土的改良成为一道重要工序,改良后的土体其抗剪强度及液塑限都会产生变化。在黏性土中加入硅酸钾溶液,进行改良,研究其抗剪强度以及液塑限的变化。对改良后的试样进行了快剪直剪试验和土体液塑限试验,探讨了硅酸钾溶液改良土的抗剪强度及其液限塑限的变化规律。进行电子扫描试验得到不同土体试样的微观结构图,并利用Image-Pro Plus图像处理软件计算含不同硅酸钾溶液浓度的改良土样的微观参数,解释其内在机理。

承压结构的弹塑性分析研究

数值模拟是承压结构应力分析设计中经常采用的方法,与弹性分析相对应的应力分类法使用较为广泛,在法规及标准中规定得较为详细。该方法要求设计者能够准确的对应力进行分类,然后使用不同的准则进行控制。但是在一些特殊结构中一次应力与二次应力的划分较为困难,有可能造成保守,也可能造成冒进。采用ANSYS软件,通过简单模型的测试与分析,提出采用极限分析法或弹塑性分析法作为替代方案,并给出了有限元软件ANSYS实现的路径与方法。

厚顶煤巷道煤柱尺寸留设及“控顶限帮”支护技术研究

为研究存在地质构造的情况下,刀把型工作面缩面期间煤柱留设尺寸以及支护难题,结合东滩煤矿1310工作面地质条件,通过理论分析及数值模拟等研究方法,确定缩面后刀把型工作面煤柱尺寸,提出了“控顶限帮”支护原理,实现对厚顶煤巷道深浅围岩的协同控制。研究结果表明,留设40 m保护煤柱,配合支护方案,可充分确保1310辅助轨顺安全稳定。结合缩面后现场监测情况,认为缩面后40 m煤柱宽度与支护方案合理可行。

Q195镀锌带钢表面横纹的原因与控制

镀锌生产线上,Q195带钢经过塔顶辊后表面出现横纹。对显示横纹的带钢进行了宏观检验、金相检验、拉伸试验和力学性能的理论计算。结果表明:该镀锌线能生产的最大带钢厚度为1.975 mm,超过该厚度的带钢受到的弯曲应力小于屈服极限,从而仅发生弹性变形。通过提高运行速度、降低退火温度,从而提高带钢强度,厚规格带钢已经不再显示因塑性变形而产生的横纹。

某医院医技住院楼超限结构分析

论文介绍了某医院医技住院楼的结构设计及超限分析情况,包括工程概况、结构体系、超限判别、性能目标等基本概况。该住院楼主要存在楼板大开洞、屋面层连体的超限情况。主要设计分析方法为在多遇地震下,利用YJK软件,采用振型分解反应谱法对规范规定的计算指标进行对比判定;在设防地震和罕遇地震作用下采用验证后的计算模型,利用Sausage软件进行弹塑性时程分析、弹塑性损伤评价;并补充楼板应力计算,等效弹性计算等分析。验证了医技住院楼的结构体系、结构布置及抗震措施能够满足超限结构的抗震目标要求。

北航青岛校区体育馆结构设计

北航青岛校区体育馆主体结构采用框架结构体系,屋盖结构采用两向正交正放网架。本工程存在扭转不规则、楼板不连续、局部穿层柱、个别构件转换等不规则项,属于超限建筑。对工程进行了小震弹性分析和大震动力弹塑性分析,针对结构的薄弱部位采取了一系列有效的加强措施。同时本工程还对屋盖与主体结构的连接方案进行了分析比较,对屋盖桁架的稳定性进行了分析,对屋盖典型的钢结构节点进行了有限元分析,对室内运动场地进行了舒适度分析,对超长结构楼盖进行了温度应力分析。结果表明:结构安全可靠,满足预设的性能目标。

RIGID FINITE ELEMENT AND LIMIT ANALYSIS

According to the lower-bound theorem of limit analysis the Rigid Finite Element Meth-od(RFEM)is applied to structural limit analysis and the linear programmings for limit analysis are deducedin this paper.Moreover,the Thermo-Parameter Method(TPM)and Parametric Variational principles(PVP)are used to reduce the computational effort while maintaining the accuracy of solutions.A better solution isalso obtained in this paper.

Analytic Solution of Elasto-Plastic Stress in Infinite Slope under Uniform Load

According to the Mohr-Coulomb yield criterion, the stress field of the infinite slope is derived under a vertical uniform load q on the top of the slope. It is indicated that elastic and elasto-plastic states would occur in the slope. When q is smaller than the critical load, q(p), the slope is in the elastic state. If q equals q(p), the slope is in the critical state, and the plastic deformation would occur along the critical angle. With the increase of q, the plastic zone would extend, and the slope is in the elasto-plastic State. If q equals limit load, the slope is in the limit equilibrium state. The slope may be divided into three zones. Some charts of the critical angle, the critical and limit load coefficients are presented in this paper.

高延性地聚合物与既有混凝土界面的黏结性能

对65个高延性地聚合物(HDGC)与既有混凝土的黏结试件进行了斜剪试验,研究了界面黏结角度、既有混凝土强度、HDGC延伸率和界面粗糙度对其界面黏结性能的影响,并基于Mohr-Coulomb屈服准则进行塑性极限分析,建立了破坏应力与界面黏结角度、内聚力和内摩擦角的计算式.结果表明:界面黏结角度对试件的失效模式起主要控制作用,界面黏结角度越大,试件的界面黏结强度越小;当既有混凝土强度提高时,试件的界面黏结强度略有降低;当HDGC延伸率为6.77%时,试件的界面黏结强度最大;随着界面粗糙度的增大,试件的界面黏结强度逐渐提高,但提高幅度呈降低趋势;建立的计算式计算结果与试验结果吻合较好.

Non-Local Analysis of Forming Limits of Ductile Material Considering Void Growth

The current study performed a finite element analysis of the strain localization behavior of a voided ductile material using a non-local plasticity formulation in which the yield strength depends on both an equivalent plastic strain measurement (hardening parameter) and Laplacian equivalent. The introduction of gradient terms to the yield function was found to play an important role in simulating the strain localization behavior of the voided ductile material. The effect of the mesh size and characteristic length on the strain localization were also investigated. An FEM simulation based on the proposed non-local plasticity revealed that the load-strain curves of the voided ductile material subjected to plane strain tension converged to one curve, regardless of the mesh size. In addition, the results using non-local plasticity also exhibited that the dependence of the deformation behavior of the material on the mesh size was much less sensitive than that with classical local plasticity and could be successfully eliminated through the introduction of a large value for the characteristic length.