三轴围压下砂浆弹塑性损伤变形过程的细观力学分析

基于对泛函势和Cauchy-Born准则,抽象出弹簧束构元和体积构元,组集两种构元的力学响应,给出了材料的弹性损伤本构关系;考虑滑移作为主要的塑性变形机制,提出了滑移构元,给出了材料的塑性本构关系;利用变形分解机制,得到了由三种构元共同描述的弹塑性损伤本构关系。阐述了在给定应变条件下弹塑性损伤本构关系的计算迭代流程。利用单轴拉伸算例详细阐述了模型参数的标定过程。对有围压作用下砂浆材料的压缩行为进行了模拟,从材料细观变形角度解释了随着围压增加,材料承载能力增加的现象。模型预测结果与试验结果符合较好,初步验证了模型具有处理非比例加载问题的能力。     

A New Static and Fatigue Compression Test Method for Composites

Abstract: A new test method to determine the compressive properties of composite materials under both static and fatigue loading was developed. The novel fixture is based on the concept of transmitting the load by a fixed ratio of end‐to‐shear loading. The end‐to‐shear load ratio is kept fixed during the test through a mechanical mechanism, which automatically maintains the gripping pressure. The combined loading method has proven very efficient in static loading and is used in the new fixture which is specially designed for fatigue testing. Optimum gripping (shear loading) and alignment of the test coupon are achieved throughout the fatigue life. The fatigue strength obtained is more reliable because bending of the specimen due to poor gripping and alignment is minimised. The application of the new fixture to static and fatigue compression is demonstrated by using unidirectional carbon/epoxy and glass/polyester composite systems. Repeatable results and acceptable failure modes are obtained under both static and fatigue loading.     

含内衬纤维缠绕筒强度分析及水压实验

给出了含内衬纤维缠绕筒承受内压时的强度分析模型,假设内衬为理想弹塑性材料,将模型分为弹性和塑性两个阶段,分别得到了缠绕筒的工作压强与爆破压强。应用该模型计算了含钢内衬纯碳纤维缠绕筒和含钢内衬纯玻璃纤维缠绕筒的工作压强和爆破压强,并预测了缠绕筒的破坏模式。水压实验结果表明,该强度分析模型与实验结果吻合较好。     

瓦楞纸板边压强度2种测试方法的分析比较

通过采用边缘不上蜡法和边缘补强法测试瓦楞纸板的边压强度,用SPSS数据统计软件分析比较了2种测试方法在进行纸箱抗压力预测计算时的拟合优劣,引用Eulerian弹性受压变形理论论证,从实验和理论上证明了2种边压强度测试方法在用于马基公式计算纸箱抗压力预测值时的可替代性。分析指出了用凯里卡特公式预测计算纸箱抗压力时,用边压强度代替原纸的综合环压,其抗压力预测值与实测值的拟合度更高。     

全轻页岩陶粒混凝土三轴受压试验及其破坏准则

利用大连理工大学的大型静、动真三轴试验机,对强度等级为LC30的全轻页岩陶粒混凝土进行了等比例三轴受压试验。试验中,观察了试件的破坏形态,测得了试件的三轴受压极限强度、塑性应变、峰值应变、总应变以及应力-应变曲线。结果表明,全轻页岩陶粒混凝土在三轴受压状态下,强度和变形较单轴受压有显著增大,并伴随有明显的平台流塑现象,也呈现四种破坏形态。因此,在工程设计中将应力平台流塑段强度及其对应的塑性应变作为轻骨料混凝土的设计强度和设计应变。此外,分析了中间主应力对三轴压的强度和变形影响,并通过三轴强度模型对极限应力进行了预测,其相对误差的绝对值均小于6%,说明试验结果是准确、可靠的。最后,基于八面体应力-应变空间分别建立了其相应的破坏准则,但前者试验点一致性较好,且拉、压子午线与静水压力轴在高压应力区有交叉点,其破坏曲面是闭口的;而后者离散性虽然较大,拟合度较差,但却同样可以很好地反映出破坏面向外扩展的趋势和子午线光滑、外凸的曲线特征。     

The effect of stress state factor on fracture of sandstones under true triaxial loading

Experimental results on rock deformation and fracture under true triaxial compression have revealed a misfit between strain state and stress state, strain state varying from generalized compression to generalized shear at σ₃ ≠ 0. This misfit can lead to data misinterpretation during the stress field reconstruction after unloading. Fracture of rock specimens under true triaxial compression occurs by a combined longitudinal/transverse shear and produces the highest dilatancy. An increase in the hydrostatic pressure level diminishes limiting values of shear strains and suppresses the dilatancy effect. A maximum of dilatancy coincides with a maximum of fresh surface area formed during the fracture of the rock. The generalized cleavage of rocks becomes energetically disadvantageous in a true triaxial compressive stress field. Some sandstone becomes more brittle under true triaxial compression (σ₂ ≠ 0) at low values of the minimal stress component (σ₃) due to high initial porosity and dilatancy.     

三轴SHPB加载下砂岩力学特性和破坏模式的试验研究

利用改造的三轴SHPB动静组合加载实验装置,对均质砂岩进行了不同围压和不同应变率下的三轴冲击压缩试验,作为对比利用RMT-150C试验机也进行了部分准静态下的三轴压缩实验。根据实验结果,分析了围压对砂岩动态冲击性能的影响,并重点讨论了冲击过程中岩石的破坏模式。研究结果表明,在围压一定的情况下,岩石的动态压缩强度随应变率的提高而提高;在应变率相同的情况下,岩石的动态压缩强度和弹性模量会随着围压的增大而增大。岩石发生破坏的临界入射能,随着围压的增大而增大。岩石单位体积吸收能与应变率之间呈线性递增关系,而且递增的程度随着围压的增加而增加。三轴冲击加载下,应变率较低时岩石内部形成压剪破裂面但整体不失稳,应变率很大时岩石破碎形成锥形块体形式。     

高频电介质强度测试仪校准方法的研究

本文基于高频电介质强度测试急需制定用于检测机构依据的校准方法,对该仪器的主要计量特性进行了研究和试验,确定了计量参数、允许误差和标准器具的选择及操作方法。     

Prediction of bending strength of long corrugated boxes

Long corrugated boxes were supported at both ends and bent by a concentrated force applied at the middle. Boxes with different lengths, cross‐sectional shapes, flute directions and board strengths were tested, using a standard compression tester with a fixed platen in accordance with ASTM D‐642. An equation was developed to relate compression strength to the various properties of the box. The correlation coefficient R² for the fit to actual data was about 0.4. Boxes having the flutes run around the box had a 20% higher compression strength than with horizontal flutes. The most significant factor was found to be the board edge crush strength. The results suggest that failure of boxes in bending is due to localized crushing at the point of application of the load, rather than whole‐box collapse. Copyright © 2001 John Wiley & Sons, Ltd.     

土工合成材料加筋粘性土的三轴试验研究

采用固结排水三轴剪切试验,研究土工合成材料加筋对粘性土体的体变、强度以及应力应变特性的影响。结果表明,加筋可以明显抑制土体的剪胀体变,但对土体的剪缩体变影响不大,加筋有利于增强高压实度土体的体积稳定性;轴向应变较低时,加筋试件的强度低于素土试件,仅当轴向应变增大到一定程度后,加筋试件的强度才逐渐高于素土试件,加筋对土体强度的增强作用存在滞后现象,且随筋材拉伸模量和加筋层数的提高,滞后现象更明显。试验结果同时表明筋材拉伸模量较低时,增加加筋层数,虽然可以一定程度提高土体的峰值强度,但对峰值后的强度提高不明显;相比而言,采用较高拉伸模量的筋材,加筋对土体残余强度的提高幅度明显高于峰值强度,对土体应力应变特性的改变也相对较大。     

Volumetric Digital Image Correlation Applied to X-ray Microtomography Images from Triaxial Compression Tests on Argillaceous Rock

Abstract:  A set of triaxial compression tests on specimens of argillaceous rock were performed under tomographic monitoring at the European Synchrotron Radiation Facility in Grenoble, France, using an original experimental set-up developed at Laboratoire 3S , Grenoble. Complete 3D images of the specimens were recorded throughout each test using X-ray microtomography. Such images were subsequently analysed using a Volumetric Digital Image Correlation software developed at the Laboratoire de Mécanique des Solides in Palaiseau, France. Full-field incremental strain measurements were obtained, which allow to detect the onset of shear strain localisation and to characterise its development in a 3D complex pattern. Volumetric Digital Image Correlation revealed patterns which could not be directly observed from the original tomographic images, because the deformation process in the zones of localised deformation was essentially isochoric (i.e. without volumetric strain), hence not associated to density changes.     

Numerical and experimental investigation of the strength of corrugated board packages

The buckling behaviour of corrugated paper packages was studied by means of an experimental and theoretical analysis. Mechanical behaviour of paperboard was first evaluated experimentally, then a local geometry FEM model, able to reproduce with a very good accuracy buckling loads obtained experimentally in the standard edge compression test, was developed. In order to investigate the buckling of a complete package, a finite element ‘corrugated board’ was introduced by means of a dedicated homogenization procedure. The FEM model of the package, assembled with this new element, can accurately predict the experimental data of incipient buckling observed during the standard box compression test, despite the few degrees of freedom and the minimal computational effort. Copyright © 2003 John Wiley & Sons, Ltd.     

On Linear Elastic Fragmentation Mechanics Under Hydrostatic Compression

In this letter we apply the Griffith’s energy balance of Linear Elastic Fracture Mechanics to predict the hydrostatic compressive strength of granular matter, as a first step towards a Linear Elastic Fragmentation Mechanics. The result is a simple law for the critical pressure, in strict analogy to the Griffith’s strength prediction, found to be mainly a function of the surface to volume ratio of particles. The influence of compaction and fragmentation evolution on the compressive strength is also quantified. Thus, this letter presents one possible approach to fragmentation mechanics. Letter to be published in INTERNATIONAL JOURNAL OF FRACTURE     

高强再生骨料混凝土的配制及性能研究

采用再生粗骨料配制强度在50MPa或更大的高强再生骨料混凝土,并对其变形能力和耐久性进行测定,为高强再生骨料混凝土在工程上的应用提供理论和实验基础。通过一系列的抗压实验确定再生粗骨料的强度极限,并通过对水灰比的调整,使配制的高强再生骨料混凝土在强度上达到设计值,并以再生粗骨料取代率为0、30%、50%、80%和100%的高强再生骨料混凝土为研究对象进行实验。当再生粗骨料取代率为30%时,对再生混凝土的强度影响不大;之后混凝土强度随再生骨料的增加而降低。高强再生骨料混凝土与天然混凝土在耐久性上具有相似的性能,可以将高强再生混凝土应用于工程中。     

毛乌素沙漠风积砂动强度特性试验研究

随着陕北油气资源的不断勘探和开发,毛乌素沙漠地区风积砂的岩土工程特性问题逐渐成为当地工程建设的制约因素。该文在均等固结条件下,采用孔压破坏标准,对毛乌素沙漠饱和风积砂进行了不同干密度和不同围压下的固结不排水等幅循环动三轴强度试验。在试验基础上,得到了不同密度不同围压下的风积砂动强度曲线和动孔隙水压力发展曲线。针对天然气压缩机的类无限循环动荷载特性,探讨了无限循环荷载作用下毛乌素沙漠饱和风积砂的动强度问题。并基于摩尔-库仑强度准则获得了适用于毛乌素沙漠风积砂在无限循环荷载作用下的等效动抗剪强度参数及破坏判据。     

垃圾土的强度与变形特性

简要回顾了环境岩土工程的发展历史,论述了垃圾土的分类和特性,从岩土力学的角度对有关垃圾土力学性质的研究现状进行了综述,其中重点讨论了垃圾土的强度和压缩变形特性,并对岩土工程师比较感兴趣的垃圾有机成分降解规律进行了介绍。还介绍了清华大学岩土工程研究所在相关方面所取得的研究成果。     

新型4层瓦楞纸板的性能分析

研究了一种新型的4层瓦楞纸板结构,并将4层瓦楞纸板和3层、5层瓦楞纸板的平压强度、边压强度、戳穿强度和耐破度性能进行比较,最后得到新型4层瓦楞纸板的主要优点是:厚度比5层瓦楞纸板要薄,节省了夹芯纸的用量,降低瓦楞纸板的成本,而且强度高,在一定情况下可以代替5层瓦楞纸板达到抗压、防震、缓冲的目的。