Effects of 'sinking in' and 'piling up' on estimating the contact area under load in indentation

The phenomena of the 'piling up' and 'sinking-in' of surface profiles in conical indentation in elastic-plastic solids with work hardening are studied using dimensional and finite-element analysis. The degree of sinking in and piling up is shown to depend on the ratio of the initial yield strength Y to Young's modulus E and on the work-hardening exponent n. The widely used procedure proposed by Oliver and Pharr for estimating contact depth is then evaluated systematically. By comparing the contact depth obtained directly from finite-element calculations with that obtained from the initial unloading slope using the Oliver-Pharr procedure, the applicability of the procedure is discussed.

Scaling relationships in conical indentation of elastic perfectly plastic solids

Using dimensional analysis and finite element calculations we derive several scaling relationships for conical indentation into elastic-perfectly plastic solids. These scaling relationships provide new insights into the shape of indentation curves and form the basis for understanding indentation measurements, including nano- and micro-indentation techniques. They are also helpful as a guide to numerical and finite element calculations of conical indentation problems. Finally, the scaling relationships are used to reveal the general relationships between hardness, contact area, initial unloading slope, and mechanical properties of solids.

边坡稳定性分析极限平衡法的简化条件

边坡稳定性分析极限平衡法在求解安全系数时,需要对条块间内力引入假定条件或某些平衡条件在求解时得不到满足.分析这些不同的假设条件对于计算结果的影响,建立一个满足极限平衡原理和合理性条件的数值优化模型.引入载荷系数,利用载荷系数与安全系数之间的单调关系,将模型的求解转化为求解一系列线性规划问题,算法中不存在数值收敛问题,且可以求出安全系数的全局最优解.通过对模型各个约束条件的变化来模拟引入的假定条件,以此探讨各种假定条件或静力平衡条件的缺失对计算结果影响及某些常用方法引入的假定条件可能带来的误差.

一类含裂隙岩质边坡的滑动弱化逐步破坏机理

含裂隙的岩土材料在剪切作用下,随着剪应变的增加,裂纹端部一定区域内的强度会表现出滑动弱化的现象.岩土材料这种性质的变化不同于粘性土结构性破坏,也不同于剪胀.在一定的载荷作用下,坡体内裂隙端部的滑动弱化使坡体内的应力重新分配,从而使得应力集中加剧,裂隙尖端进一步扩展,造成岩体结构性的破坏,乃至整个滑面的贯通直至发生滑坡.因此,滑动弱化是一类含裂隙岩质边坡滑坡的机理.

爆破方法识别滑带试验研究

以往对滑坡体中软弱层与滑带的识别主要依赖十钻孔并辅之以工程师的经验。采用在钻孔中进行爆破的方法，通过对地表接收信号的波形分析即可十分方便地识别出软弱层与滑带。简耍阐述了该方法的理论依据，通过对现场爆破实验测量信号的分析可以发现，该方法可以减少钻孔数量以及提高滑带识别的精度与效率。

三维简化Janbu法分析边坡稳定性的扩展

对三维简化的Janbu法进行了扩展,使得离散后在同一行上的各条块在水平横向的安全系数相等以及在同一列上的条块在水平纵向的安全系数相等,得到不同行(列)的安全系数,最后通过各条块底滑面的几何特性与受力分析给出其独立的安全系数以及各条块潜在的滑动方向.该方法拓展了传统极限平衡方法只给出坡体总体安全系数的思路,可对坡体局部稳定性和潜在滑动方向进行判定.该方法可适用于任意形状的滑面,还可分析包括考虑孔隙水压力、地质体分层、上覆载荷以及地震力等其他形式的外载.

Relationship Between Contact Stiffness, Contact Depth, and Mechanical Properties for Indentation in Linear Viscoelastic Solids Using Axisymmetric Indenters

We derive a relationship between the initial unloading slope, contact depth, and the instantaneous relaxation modulus for indentation in linear viscoelastic solids by a rigid indenter with an arbitrary axisymmetric smooth profile. Although the same expres

地表条件对坡面产流的影响

本文将复杂地表条件对坡面流运动的影响概化为阻力的变化,运用运动波理论和修正的Green-Ampt入渗模型,建立了能够反映地表条件影响的坡面降雨入渗产流模型,数值结果与实验符合较好,运用该模型分析了植被、地形、坡长、坡度等地表条件对坡面产流过程的影响.

Relationships between hardness, elastic modulus, and the work of indentation

The work done during indentation is examined using dimensional analysis and finite element calculations for conical indentation in elastic-plastic solids with work hardening. An approximate relationship between the ratio of hardness to elastic modulus and the ratio of irreversible work to total work in indentation is found. Consequently, the ratio of hardness to elastic modulus may be obtained directly from measuring the work of indentation. Together with a well-known relationship between elastic modulus, initial unloading slope, and contact area, a new method is then suggested for estimating the hardness and modulus of solids using instrumented indentation with conical or pyramidal indenters.

Scaling approach to conical indentation in elastic-plastic solids with work hardening

We derive, using dimensional analysis and finite element calculations, several scaling relationships for conical indentation in elastic-plastic solids with work hardening. Using these scaling relationships, we examine the relationships between hardness, contact area, initial unloading slope, and mechanical properties of solids. The scaling relationships also provide new insights into the shape of indentation curves and form the basis for understanding indentation measurements, including nano- and micro-indentation techniques. They may also be helpful as a guide to numerical and finite element calculations of indentation problems.

Plot Erosion Model Using Gray Relational Analysis Method

The main factors affecting interrill erosion-including runoff discharge, rainfall intensity, mean flow velocity, and slope gradient-were analyzed by using a gray relational analysis. An equation for interrill erosion was derived by coupling this analysis with dimensional and regression analyses. The values of erosion rates predicted by this equation were in good agreement with experimental observations.

水位变化引起分层边坡滑坡的实验研究

通过对分层的边坡在水位变化时滑坡的模拟实验,考察了分层坡体的滑坡模式、坡体变形、破坏和渗流引起的滑坡,重点考察了水位涨落速度对坡体稳定的影响,以及坡面从产生张拉裂缝直到形成滑面的整个过程,并对这类滑坡中的现象给出了定性解释.最后用有限元对实验坡体进行了应力和位移的静力场分析,计算结果与实验结果基本一致.

Liquefaction and Displacement of Saturated Sand Under Vertical Vibration Loading

In order to investigate the influence of the vertical vibration loading on the liquefaction of saturated sand, one dimensional model for the saturated sand with a vertical vibration is presented based on the two phase continuous media theory. The development of the liquefaction and the liquefaction region are analyzed. It is shown that the vertical vibration loading could induce liquefaction. The rate of the liquefaction increases with the increase of the initial limit strain or initial porosity or amplitude and frequency of loading, and increases with the decrease of the permeability or initial modulus. It is shown also that there is a phase lag in the sand column. When the sand permeability distribution is non-uniform, the pore pressure and the strain will rise sharply where the permeability is the smallest, and fracture might be induced. With the development of liquefaction, the strength of the soil foundation becomes smaller and smaller. In the limiting case, landslides or debris flows could occur.

Modeling Nonlinear Peeling of Ductile Thin Films-Critical Assessment of Analytical Bending Models Using FE Simulations

Three analytical double-parameter criteria based on a bending model and a two-dimensional finite element analysis model are presented for the modeling of ductile thin film undergoing a nonlinear peeling process. The bending model is based on different governing parameters: (1) the interfacial fracture toughness and the separation strength, (2) the interfacial fracture toughness and the crack tip slope angle, and (3) the interfacial fracture toughness and the critical Mises effective strain of the delaminated thin film at the crack tip. Thin film nonlinear peeling under steady-state condition is solved with the different governing parameters. In addition, the peeling test problem is simulated by using the elastic-plastic finite element analysis model. A critical assessment of the three analytical bending models is made by comparison of the bending model solutions with the finite element analysis model solutions. Furthermore, through analyses and comparisons for solutions based on both the bending model and the finite element analysis model, some connections between the bending model and the finite element analysis model are developed. Moreover, in the present research, the effect of different selections for cohesive zone shape on the ductile film peeling solutions is discussed.

Experimental Investigation and Numerical Simulation on the Effect of Fissure Water Pressure in Vertical Sliding Surface

This paper studies the effect of fissure water pressure in different fractures on the critical angle of landslide by laboratory investigation and numerical simulation in order to understand the mechanisms of fissure water pressure on landslide stability. Laboratory observations show that the effect of fissure water pressure on the critical angle of landslide is little when the distance between water-holding fracture and slope toe is three times greater than the depth of fissure water. These experimental results are also simulated by a three-dimensional face-to-face contact discrete element method. This method has included the fissure water pressure and can accurately calculate the critical angle of jointed slope when fissure water pressure in vertical sliding surface exists. Numerical results are in good agreement with experimental observations. It is revealed that the location of water-holding structural surface is important to landslide stability. The ratio of the distance between water-holding fissure and slope toe to the depth of fissure water is a key parameter to justify the effect of fissure water pressure on the critical angle of landslide.