岩石变形破坏过程中的能量传递和耗散研究

岩石变形破坏的过程是和外界产生能量交换的过程。从理论上分析了用能量方法研究岩石破坏问题的合理性,以及岩石在变形过程中弹性能、塑性能、表面能、辐射能、动能之间相互转化的过程、计算原理、以及对岩石破坏所起的不同作用。并分别从宏观和微观的角度研究了在不同的变形阶段中岩石能量耗散与释放问题。在宏观上,岩石变形前期以弹性应变能的方式存储外界提供的能量,同时又通过损伤演化等向外界耗散能量;变形的后期以剧烈的能量释放为主。微观上,存在多种引起岩石应变硬化和应变软化的机制,岩石存储能量还是向外界释放能量取决于这些微观机制竞争的最后结果,基于此推导了岩石变形中能量的传递方程,用试验研究了能量的转化和平衡,以及耗散能和释放能之间的比例关系。结果表明能量耗散导致岩石强度的降低,而能量释放是造成岩石灾变破坏的真正原因。从能量耗散与释放的观点研究岩石的破坏,可以从本质上把握岩石变形和破坏的物理机理,寻找岩石破坏的真正原因,为实际工程提供参考。     

Mechanical/Thermal Sources in a Micropolar Thermoelastic Medium Possessing Cubic Symmetry without Energy Dissipation

The present problem is concerned with the study of the deformation of a thermoelastic micropolar solid possessing cubic symmetry under the influence of various sources acting on the plane surface. The analytic expressions of displacement components, microrotation, force stress, couple stress, and temperature distribution are obtained in the physical domain for the Green and Nagdhi (G–N) theory of thermoelasticity by applying the integral transforms. A numerical inversion technique has been applied to obtain the solution in the physical domain. The numerical results are presented graphically for a particular material.     

On the Mechanism of Energy Dissipation in a Fatigue Crack

Experimental studies of specimens with a Mode-I edge crack in bending vibration have demonstrated that energy dissipation in the fatigue crack is mainly due to an elastoplastic zone at the crack tip. The absolute level of energy dissipation in the crack is unambiguously governed by the stress intensity factor range and is independent of specimen dimensions and crack location.     

Illuminating Origins of Impact Energy Dissipation in Mechanical Metamaterials

Elastomeric mechanical metamaterials have revealed striking ability to attenuate shock loads at the macroscopic level. Reports suggest that this capability is associated with the reversible elastic buckling of internal beam constituents observed in quasistatic characterizations. Yet, the presence of buckling members induces non‐affine response at the microscale, so that clear understanding of the exact energy dissipation mechanisms remains clouded. In this report, the authors examine a mechanical metamaterial that exhibits both micro‐ and macroscopic deformations under impact loads and devise an experimental method to visualize the resulting energy dissipation mechanisms. By illuminating the dynamic distribution of strain in the metamaterial, the authors uncover a rational way to program the macroscopic deformation and enhance impact mitigation properties. The results emphasize that mechanical metamaterials clearly integrate materials science and structural engineering, encouraging future interdisciplinary studies to capitalize on the opportunities.

     

The Effect of Gravity on Plane Waves in a Rotating Thermo-Microstretch Elastic Solid for a Mode-I Crack with Energy Dissipation

The present article is aimed at studying the effect of gravity on the general model of the equations of generalized thermo-microstretch for a homogeneous isotropic elastic half-space solid rotating about the fixed axis of rotation and whose surface is subjected to a Mode-I crack problem considered. The problem is in the context of the Green and Naghdi theory (GN). The normal mode analysis is used to obtain the exact expressions for the displacement components, force stresses, temperature, couple stresses, and microstress distribution. The variations of the considered variables perpendicular to the axis of rotation are illustrated graphically. Comparisons are made with the results in the presence and absence of gravity and rotational frequency of a particular case for the generalized micropolar thermoelasticity elastic medium (without microstretch constants) between the two types (II, III).     

耗能支撑钢筋砼框架结构的工程应用

采用耗能支撑钢筋混凝土框架结构设计了地处地震高烈度区的江苏新沂市某商业楼。文中阐述了该工程所采用的抗震设计方法,对所研制的新型复合耗能器进行了非线性有限元分析,简述了结构设计与施工中的一些技术问题的处理。     

结构抗震消能控制的试验与应用研究

为了改善高层剪力墙结构的抗震性能,根据结构控制的原理提出了一种新型剪力墙—沿竖向消能的带竖缝剪力墙。首先,进行了竖缝处消能装置的剪切—摩擦试验,研究了这种消能装置的受力机理和消能机理,给出了荷载—位移骨架曲线的理论计算方法。其次,进行了带有此消能装置的一层带竖缝剪力墙和普通实体墙的低周反复荷载试验,对比研究了这两类剪力墙的破坏机理和滞回特性,试验表明这种新型消能剪力墙具有良好的抗震性能。接着,讨论了这种剪力墙的消能计算方法。最后,介绍了消能剪力墙的一个工程应用实例。     

螺栓接头非线性模型及其波能耗散

建立了在高频情况下一维构件的波传播模型，针对工程中常见的螺栓连接梁结构，讨论了波在其中传播的特性及能量耗散问题，提出了一种简化的非线性接头模型。分析与实验结果表明：这种非线性模型更能接近实际。波通过梁的螺栓连接时，存在着能量耗散，螺栓松紧程度对能量耗散有较大的影响。在共振频率处，连接部分发生较大的折射。     

岩石劈裂拉伸试验的能量耗散分析

利用直径50 mm的霍普金森试验装置,对长径比为0.5的三种岩石进行动态平台巴西圆盘劈裂拉伸试验,分析了岩石试件在动态加载过程中能量的应变率效应、能量耗散特征和破坏形态。结果表明:反射能与入射能比值大于50%,透射能与入射能比值在10%以内,试件耗散能与入射能比值在10%~45%,因此,试件端部粉碎三角区的面积大小存在差异;在进行冲击试验过程中为提高岩石试件破碎的能量利用率,需尽量避开应变率200~300 s-1范围;岩石的抗拉强度、弹性模量、应力峰值的对数与能量耗散的对数具有显著线性关系。     

层状板中Lamb波的频散特性研究

利用矩阵递推方法，建立了层状板中Ｌａｍｂ波的特征方程以及相应的位移和应力分布计算公式，由此分析了双层板、软夹层板和硬夹层板中Ｌａｍｂ波的频散特性，特别指出软夹层的存在对Ｌａｍｂ波的频散特性有显著影响。该结论对工程测试分析有一定指导意义。     

桩内应力波的频散现象及数学模型

本文采用广义变分原理建立了一种考虑圆杆内横向运动影响的纵波理论,用于求解锤击杆端所生成的波场.所得到的解包括两部分:局限于杆端的驻波场和具有频散的行波场;理论结果与实验结果吻合较好,对于桩的动测技术具有指导意义.     

Phase and Dispersion of Cylindrical Surface Waves

Most theoretical and experimental work on surface waves does not take into account dispersion. When propagating along a flat planar half space, surface waves are known as Rayleigh waves and are not dispersive. When the radii of curvature are large, surface waves behave like Rayleigh waves. However, when the radii are small, dispersion becomes a contributing factor. Experimental measurements indicate that along with dispersion, there appears to be a strong phase shift effect as the wave propagates along the circumferential path of cylindrical specimens. The phase shift effect is observed even under conditions where dispersion is not detected. Classical theories provide the velocity-frequency equations, which represent the dispersion relationships, for surface waves. An alternate theoretical approach is discussed in this article that demonstrates the phase-dispersion relationship for cylindrical surface waves. Experimental data support the theoretical conclusions and indicate phase shift is directly related to the radius of curvature to an extent much more sensitive than dispersion.     

Spatial Heterogeneity Directs Energy Dissipation in Condylar Fibrocartilage (Small 37/2023)

Condylar fibrocartilage with structural and compositional heterogeneity can efficiently orchestrate load-bearing and energy dissipation, making the temporomandibular joint (TMJ) survive high occlusion loads for a prolonged lifetime. How the thin condylar fibrocartilage can achieve efficient energy dissipation to cushion enormous stresses remains an open question in biology and tissue engineering. Here, three distinct zones in the condylar fibrocartilage are identified by analyzing the components and structure from the macro-and microscale to the nanoscale. Specific proteins are highly expressed in each zone related to its mechanics. The heterogeneity of condylar fibrocartilage can direct energy dissipation through the nano-micron–macro gradient spatial scale, by atomic force microscope (AFM), nanoindentation, dynamic mechanical analyzer assay (DMA), and the corresponding energy dissipation mechanisms are exclusive for each distinct zone. This study reveals the significance of the heterogeneity of condylar fibrocartilage in mechanical behavior and provides new insights into the research methods for cartilage biomechanics and the design of energy-dissipative materials.     

Model of Fractional Heat Conduction in a Thermoelastic Thin Slim Strip under Thermal Shock and Temperature-Dependent Thermal Conductivity

The present paper paper, we estimate the theory of thermoelasticity a thin slim strip under the variable thermal conductivity in the fractional-order form is solved. Thermal stress theory considering the equation of heat conduction based on the time-fractional derivative of Caputo of order α is applied to obtain a solution. We assumed that the strip surface is to be free from traction and impacted by a thermal shock. The transform of Laplace (LT) and numerical inversion techniques of Laplace were considered for solving the governing basic equations. The inverse of the LT was applied in a numerical manner considering the Fourier expansion technique. The numerical results for the physical variables were calculated numerically and displayed via graphs. The parameter of fractional order effect and variation of thermal conductivity on the displacement, stress, and temperature were investigated and compared with the results of previous studies. The results indicated the strong effect of the external parameters, especially the time-fractional derivative parameter on a thermoelastic thin slim strip phenomenon.     

SMA耗能器的阻尼性能试验研究

设计并制作了伸缩式形状记忆合金耗能阻尼器，并对此器件进行了试验研究。试验结果与理论分析结果吻合程度较好，表明器件的设计是合理的、加工制作的工艺满足了理论要求，为该器件的工程实际应用积累了实践经验。     

基于模态应变能耗散率理论的结构损伤识别方法

本提出了基于模态应变能耗散率理论的一种新的结构损伤识别方法。表示结构损伤的损伤变量的概念来自于材料领域，并推广到了构件和结构；在此基础上，结构单元的损伤变量是通过建立模态应变能耗散率和相应的结构损伤前后的应变能变化的关系而获得。该方法所要求的结构损伤前后的振型模态可以是不完备的。对测量噪声的影响具有较强的鲁棒性。最后，通过数值算例的分析结果说明，该方法简便、有效，可定位结构的损伤和识别损伤的程度。     

Energy Dissipation and Apparent Viscosity of Semi-solid Metal during Rheological Processes Part Ⅰ： Energy Dissipation

The energy dissipation caused by the viscous force has great effects on the flow property of semi-solid metal during rheological processes such as slurry preparing, delivering and cavity filling. Experimental results in this paper indicate that the viscous friction between semi-solid metal and pipe wall, the collisions among the solid particles, and the liquid flow around particles are the three main types of energy dissipation. On the basis of the hydromechanics, the energy dissipation calculation model is built. It is demonstrated that the micro-structural parameters such as effective solid fraction, particle size and shape, and flow parameters such as the mean velocity, the fluctuant velocity of particles and the relative velocity between the fluid and solid phase, affect the energy dissipation of semi-solid metal.     

Mechanical Response and Energy Dissipation Analysis of Heat-Treated Granite Under Repeated Impact Loading

The mechanical behaviors and energy dissipation characteristics of heat-treated granite were investigated under repeated impact loading. The granite samples were firstly heat-treated at the temperature of 20°C, 200°C, 400°C, and 600°C, respectively. The thermal damage characteristics of these samples were then observed and measured before impact tests. Dynamic impact compression tests finally were carried out using a modified split-Hopkinson pressure bar under three impact velocities of 12 m/s, 15 m/s, and 18 m/s. These test results show that the mineral composition and the main oxides of the granite do not change with these treatment temperatures. The number of microcracks and microvoids decreases in the sample after 200°C treatment. The mechanical properties of a sample after 600°C treatment were rapidly deteriorated under the same impact velocity. The average of peak stress is much smaller than those after 20°C, 200°C and 400°C treatments. The heat-treated samples have an energy threshold each. When the dissipated energy of a sample under a single impact is less than this threshold, the repeated impacts hardly lead to further damage accumulation even if its total breakage energy dissipation (BED) density is large. Under the same number of repeated impacts, the cumulative BED density of a sample after 600°C treatment is the largest and its damage evolves most quickly. The total BED density of the sample after 200°C treatment is the highest, which implies that this sample has better resistance to repeated impact, thus having less crack initiation and growth.     

Dissipation Measurements in Steel Sheets Under Cyclic Loading by Use of Infrared Microthermography

Abstract:  Heterogeneous dissipation in steel sheets due to cyclic loading is difficult to measure, especially in the transverse direction because of the high conductivity and low thickness of the sheets. The goal of this article is thus to develop an experimental protocol allowing for the dissipation field determination from infrared thermography. The protocol is based on a specific differential measurement and an asynchronous acquisition. It reduces measurement artefacts due to coating, rigid body motion, convection, and optical deleterious effects. It is eventually applied to different specimens.