On anisotropic continuous damage of plates in Flexure

Internal damage due to fissuration results in an overall anisotropic material behaviour. A scalar damage parameter does not allow one to model a direction dependent response of continuously damaging solids. Employing the idea that the scalar damage parameter can be associated with an appropriate strain a damage tensor related to strains is introduced. The overall elastic properties are determined using a simplified form of the sensor function representations and the stress-strain relations regarding the overall response are given. For combined stress states an uncoupled damage theory is derived for materials with no lateral deformability under axial stress. Both brittle-ductile and elastic-brittle cases are studied using circular plates, for the elastic-brittle case only the governing differential equation are presented.     

Mechanical damage of an anisotropic porous rock in cyclic triaxial tests

This paper presents an extensive laboratory investigation of the mechanical properties of a porous sandstone which exhibits transversely isotropic behaviour. Particular attention has been paid to the influence of the structural anisotropy on the progressive development of pre-peak damage. Uniaxial and triaxial cyclic tests were performed for several orientations of the isotropy planes with respect to the principal stress directions in order to quantify the irreversible strains and the changes of oriented moduli with the cumulative damage. Two main mechanisms are involved throughout the loading process: compaction and microcracking. Compaction is active at all stress levels. In the uniaxial tests, both mechanisms are shown to be strongly influenced by the inclination of loading with respect to the isotropy planes. However, with increased confining pressures, the influence of anisotropy is significantly reduced.     

Modelling the effect of damage on transport processes in concrete

The calculation of corrosion current density, during the process of electrochemical steel corrosion in concrete, requires modelling of the following physical and electrochemical processes: transport of capillary water, oxygen and chloride through the concrete cover, immobilization of chloride in the concrete, transport of OH⁻ ions through electrolyte in concrete pores and cathodic and anodic polarization. The paper deals with a 3D numerical model for transport of capillary water, oxygen and chloride through the concrete. The model is formulated in the framework of continuum mechanics following basic principles of irreversible thermodynamics. The mechanical part of the model is based on the hygro-thermo dependent microplane model of concrete. Damage and cracking phenomena are modelled within the concept of smeared cracks (weak discontinuity). The interaction between the non-mechanical processes (distribution of temperature, capillary water, oxygen and chloride) and mechanical properties of concrete (damage) is taken into account. The strong and weak formulations of the model and the implementation into a 3D finite element code are discussed. The formulation is restricted to the processes leading to depassivation of reinforcement. The application of the model is illustrated on a numerical example in which the transient 3D finite element analysis of RC slab is carried out to investigate the influence of damage of concrete on depassivation time of reinforcement. In the analysis, the undamaged and damaged parts of previously loaded RC slabs are exposed to the aggressive influence of seawater. Due to external load, the RC slab was partly cracked before the exposure to seawater. Consequently, the damaged part of the slab exhibits a much shorter depassivation time than the undamaged part. This is due to the cracking of concrete, which significantly accelerates processes that are relevant for depassivation of reinforcement. It is shown that depassivation in the cracked concrete is reached almost immediately after the attack of chlorides. The numerical results are in good agreement with the available experimental observations.     

Modelling the dynamics of design error induced rework in construction

Rework that is experienced in construction projects is often caused by errors made during the design process. Factors that contribute to design errors are identified and used to design and develop a systems dynamics model, which is used to simulate a number of practical scenarios that can be used to reduce design errors and rework. The model presented in this paper can enable design and project managers to understand better the process of design documentation and how design errors occur in construction projects.     

Modelling of blast-induced damage in tunnels using a hybrid finite-discrete numerical approach

This paper presents the application of a hybrid finite-discrete element method to study blast-induceddamage in circular tunnels. An extensive database of field tests of underground explosions above tunnelsis used for calibrating and validating the proposed numerical method; the numerical results areshown to be in good agreement with published data for large-scale physical experiments. The method isthen used to investigate the influence of rock strength properties on tunnel durability to withstand blastloads. The presented analysis considers blast damage in tunnels excavated through relatively weak（sandstone） and strong （granite） rock materials. It was found that higher rock strength will increase thetunnel resistance to the load on one hand, but decrease attenuation on the other hand. Thus, undercertain conditions, results for weak and strong rock masses are similar.
2014 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting byElsevier B.V. All rights reserved.     

Micromechanics of compressive failure and spatial evolution of anisotropic damage in Darley Dale sandstone

The micromechanics of compressive failure in Darley Dale sandstone (with initial porosity of 13%) was investigated by characterizing quantitatively the spatial evolution of anisotropic damage under the optical and scanning electron microscopes. Two series of triaxial compression experiments were conducted at the fixed pore pressure of 10 MPa and confining pressures of 20 and 210 MPa, respectively. For each series, three samples deformed to different stages were studied. Failure in the first series was by brittle faulting. In contrast, failure in the second series was ductile, involving shear-enhanced compaction and distributed cataclastic flow. In the ductile series, crack density and acoustic emission activity both increased with the development of strain hardening. The stress-induced cracking was relatively isotropic. In the brittle series, crack density increased with the progressive development of dilatancy, with spatial distributions indicative of clustering of damage at the peak stress and shear localization in the strain softening stage. Dilatancy was associated with significant anisotropy in stress-induced cracking, that was primarily due to intragranular and intergranular cracking with a preferred orientation parallel to the maximum principal stress. Compared with published data for Westerly granite and San Marcos gabbro (with porosities of the order of 1%) and for Berea sandstone (with porosity of 21%), there is an overall trend for the stress-induced anisotropy (in a sample deformed to near the peak stress) to decrease with increasing porosity. The sliding wing crack model was adopted to analyze the evolution of anisotropic damage, using a friction coefficient and fracture toughness inferred from stress states at the onset of dilatancy. Significant discrepancy exists between the model prediction and microstructural data on stress-induced anisotropy, which is possibly due to limitations intrinsic to the microscopy technique as well as the sliding wing crack model.     

Modelling the dynamics of design error induced rework in construction: comment

The bridging of different research disciplines such as computer modelling and design practice requires full understanding of both. Privileging one area of investigation while simplifying the other is not a feasible option. This approach is likely to produce work that scarcely reflects the actual complexity of the phenomena discussed.     

深基坑开挖引起的建筑物破坏风险评估

对于深基坑工程来说,评价开挖引起的地表沉降导致建筑物的潜在破坏风险是非常重要的。在以前的研究中,常用简单的指标如角变位和挠曲度来进行建筑物的破坏评价,这些评价方法不能反映不同上部结构形式和邻近施工的影响。本文综合地表沉降曲线形式、建筑物结构的几何尺寸、材料的临界应变以及建筑物的破坏评价准则,采用建筑物的裂缝宽度来评价深基坑开挖引起的建筑物潜在破坏,并以砖混结构为例,给出了整个风险评估过程。     

花岗石自动砂锯锯条拉杆的革新

一、锯条拉杆的作用要明白锯条拉杆的作用,请先看图1。在图1中,下部是一块花岗石荒料,荒料的正上方是锯条。锯条拉杆把锯条装夹在锯框当中。电机和传动系统驱动着锯框做前后摆动进行作业,从而完成锯切花岗石的工作。(因篇幅限制,图1中花岗石荒料和锯条未按比例画出,仅做示意)。锯条拉杆的作用不仅是把锯条装     

城市隧道施工引起建筑物变形的损坏评估

近年来随着城市地铁建设的快速发展,隧道施工过程中引起地面建筑物或其他结构变形而产生的损坏问题屡见不鲜。地铁建设中需要对大量的建筑物开展变形损坏风险评估工作,而科学的建筑物变形及其损坏的评估方法方面的研究尚很不成熟。针对量大面广的多层砖混结构,研究隧道施工可能造成的建筑损坏问题。利用北京市在20世纪70年代对建筑裂缝控制的研究基础和工程应用经验、特别是扎实可靠的数据得到的最小曲率控制参数,基于对建筑物在隧道施工影响下变形特征的研究和沉降预测的修正刚度法,避开不容易准确估计的建筑材料模量、截面惯性矩等参数,直接根据建筑物的沉降曲线形态,得到用拉应变控制的评估方法,发展了用最小曲率参数来控制隧道施工引起沉降的有效方法。这种评估方法与用拉应变控制的方法取得很好的一致性。     

Thermo-mechanical properties of Indian and other granites

The knowledge of thermo-mechanical and transport properties of granites is required to understand and model a number of processes in the earth crust such as folding, geothermal activity, magmatic intrusions, plate tectonics and nuclear waste disposal. Authors have studied various thermo-mechanical properties of Indian granite (IG) at high temperatures in the range of 30–160 °C, keeping in view the highest temperatures expected in underground nuclear waste repositories. These properties are Young's modulus, uniaxial compressive strength, tensile strength, Poisson's ratio, coefficient of linear thermal expansion, creep behaviour and the development of micro-crack on heating using scanning electron microscope (SEM). In addition, a literature survey was carried out to collect data on the properties of granites at high temperatures including first five properties mentioned above for IG and some other properties such as viscosity, permeability, melting point, specific heat, thermal conductivity and thermal diffusivity. The information gathered in this paper would be useful in thermo-mechanical characterisation of granites for modelling of several geological phenomena.     

硅酸铝微珠在人造花岗石中的应用

长期以来,人造花岗石普遍是用热固性树脂与填充料、增强材、内部脱模剂、硬化剂等辅助原料配合而成的树脂混合料注入所需形状的金属模具,加热固化而成.为防止强度降低,成形制品的厚度通常为10～ 30mm.由于板体规格越大,质量越重,不便于生产和安装过程中的装卸.因此,尽可能减少板体厚度,使其轻质.但板体变薄,其自身强度降低,用...     

Modelling biological and chemically induced precipitation of calcium phosphate in enhanced biological phosphorus removal systems

The biologically induced precipitation processes can be important in wastewater treatment, in particular treating raw wastewater with high calcium concentration combined with Enhanced Biological Phosphorus Removal. Currently, there is little information and experience in modelling jointly biological and chemical processes. This paper presents a calcium phosphate precipitation model and its inclusion in the Activated Sludge Model No 2d (ASM2d). The proposed precipitation model considers that aqueous phase reactions quickly achieve the chemical equilibrium and that aqueous-solid change is kinetically governed. The model was calibrated using data from four experiments in a Sequencing Batch Reactor (SBR) operated for EBPR and finally validated with two experiments. The precipitation model proposed was able to reproduce the dynamics of amorphous calcium phosphate (ACP) formation and later crystallization to hydroxyapatite (HAP) under different scenarios. The model successfully characterised the EBPR performance of the SBR, including the biological, physical and chemical processes.     

Numerical simulations of rock mass damage induced by underground explosion

The damage prediction of rock mass under blast loads induced by accidental explosions, rock bursts or weapon attacks is crucial in rock engineering. In this paper, parametric studies are conducted to evaluate the effect of loading density, rock mass rating (RMR) and weight of charge on the rock mass damage induced by underground explosions. The numerical simulations are carried out based on the transient dynamic finite element program ANSYS-LSDYNA. The numerical model was calibrated against the data obtained from a field blast test. A fully coupled numerical analysis, incorporating the explosion process, has been performed, where the large deformation zone near the charge is solved by the Arbitrary Lagrange–Euler (ALE) method. The deformable modulus and compressive strength of rock mass of granite are estimated by the RMR system. The peak particle velocity (PPV) damage criterion and the plastic strain criterion were adopted to study the damage zone around the charge hole, and an empirical formula considering the effects of loading density, RMR and weight of charge was obtained to estimate the damage zone in granite based on the numerical results.     

DNA damage induced by wastewater from cocoa industry in two prokaryotic systems

In this study, the potential genotoxic and mutagenic effects of cocoa industry wastewater was assessed using SOS Chromo and Ames fluctuation tests, respectively. The physico-chemical analyses of the wastewater were also carried out. The SOS Chromo and Ames fluctuation tests results showed that cocoa industry wastewater can induce different levels of DNA damage and mutagenic potential at the different concentrations used in this study. Salmonella typhimurium TA98 was more sensitive than TA100 strain, indicating frameshift mutation as a possible mechanism of DNA damage. High concentrations of Pb, Cd, Cr, Ni and Cu in the tested sample were possibly responsible for the observed mutagenicity and genotoxicity.     

花岗石自动砂锯喷淋管的改进

用自动砂锯锯切花岗石的时候,要把砂浆喷淋到花岗石荒料的顶部。并且要使砂浆均匀的分布到每一条锯缝当中。这是因为砂浆中所包含的钢砂实际上是切割石板的刀具。既然是刀具,那它就必须接触到要切的部位。砂浆喷淋不到的部位就是钢砂接触不到的部位。当然也是不能有效锯切花岗石的部位。