Roughness characterization and shearing dislocation failure for rock-backfill interface

Shearing dislocation is a common failure type for rock–backfill interfaces because of backfill sedimentation and rock strata movement in backfill mining goaf.This paper designed a test method for rock–backfill shearing dislocation.Using digital image techno-logy and three-dimensional(3D)laser morphology scanning techniques,a set of 3D models with rough joint surfaces was established.Further,the mechanical behavior of rock–backfill shearing dislocation was investigated using a direct shear test.The effects of interface roughness on the shear–displacement curve and failure characteristics of rock–backfill specimens were considered.The 3D fractal dimen-sion,profile line joint roughness coefficient(JRC),profile line two-dimensional fractal dimension,and the surface curvature of the frac-tures were obtained.The correlation characterization of surface roughness was then analyzed,and the shear strength could be measured and calculated using JRC.The results showed the following:there were three failure threshold value points in rock–backfill shearing dis-location:30%–50%displacement before the peak,70%–90%displacement before the peak,and 100%displacement before the peak to post-peak,which could be a sign for rock–backfill shearing dislocation failure.The surface JRC could be used to judge the rock–backfill shearing dislocation failure,including post-peak sliding,uniform variations,and gradient change,corresponding to rock–backfill disloca-tion failure on the field site.The research reveals the damage mechanism for rock–backfill complexes based on the free joint surface,fills the gap of existing shearing theoretical systems for isomerism complexes,and provides a theoretical basis for the prevention and control of possible disasters in backfill mining.

Research Progress in the Failure Behavior onthe Interface of Thermal Barrier Coatings

This paper mainly introduces the research progress on interface failure behavior in high-temperature alloy surface thermal barrier coating systems.The degradation failure and structural evolution behavior during high-temperature service were analyzed for the matrix/bonding layer interface,bonding layer/TGO interface,and TGO/ceramic layer interface in thermal barrier coatings.The research focus and direction that affect the interface performance of thermal barrier coatings were proposed.

Change of the mode of failure by interface friction and width-to-height ratio of coal specimens

Bumps in coal mines have been recognized as a major hazard for many years. These sudden and violent failures around mine openings have compromised safety, ventilation and access to mine workings.Previous studies showed that the violence of coal specimen failure depends on both the interface friction and width-to-height（W/H） ratio of coal specimen. The mode of failure for a uniaxially loaded coal specimen or a coal pillar is a combination of both shear failure along the interface and compressive failure in the coal. The shear failure along the interface triggered the compressive failure in coal. The compressive failure of a coal specimen or a coal pillar can be controlled by changing its W/H ratio. As the W/H ratio increases, the ultimate strength increases. Hence, with a proper combination of interface friction and the W/H ratio of pillar or coal specimen, the mode of failure will change from sudden violent failure which is brittle failure to non-violent failure which is ductile failure. The main objective of this paper is to determine at what W/H ratio and interface friction the mode of failure changes from violent to non-violent. In this research, coal specimens of W/H ratio ranging from 1 to 10 were uniaxially tested under two interface frictions of 0.1 and 0.25, and the results are presented and discussed.

Laboratory investigation into effect of bolt profiles on shear behaviors of bolt-grout interface under constant normal stiffness (CNS) conditions

Rock bolts have been widely used for stabilizing rock mass in geotechnical engineering.It is acknowledged that the bolt profiles have a sound influence on the support effect of the rock bolting system.Previous studies have proposed some optimal rib parameters(e.g.rib spacing);unfortunately,the interface shear behaviors are generally ignored.Therefore,determination of radial stress and radial displacement on the bolt-grout interface using traditional pull-out tests is not possible.The load-bearing capacity and deformation capacity vary as bolt profiles differ,suggesting that the support effect of the bolting system can be enhanced by optimizing bolt profiles.The aim of this study is to investigate the effects of bolt profiles(with/without ribs,rib spacing,and rib height)on the shear behaviors between the rock bolt and grout material using direct shear tests.Thereby,systematic interfacial shear tests with different bolt profiles were performed under both constant normal load(CNL)and constant normal stiffness(CNS)boundary conditions.The results suggested that rib spacing has a more marked influence on the interface shear behavior than rib height does,in particular at the post-yield stage.The results could facilitate our understanding of bolt-grout interface shear behavior under CNS conditions,and optimize selection of rock bolts under in situ rock conditions.

Deformation tests and failure process analysis of an anchorage structure

In order to study the failure process of an anchorage structure and the evolution law of the body＇s defor- mation field, anchor push-out tests were carried out based on digital speckle correlation methods （DSCM）. The stress distribution of the anchorage interface was investigated using the particle flow numerical simulation method. The results indicate that there are three stages in the deformation and fail- ure process of an anchorage structure： elastic bonding stage, a de-bonding stage and a failure stage. The stress distribution in the interface controls the stability of the structure. In the elastic bonding stage, the shear stress peak point of the interface is close to the loading end, and the displacement field gradually develops into a ＂V＂ shape, in the de-bonding stage, there is a shear stress plateau in the center of the anchorage section, and shear strain localization begins to form in the deformation field. In the failure stage, the bonding of the interface fails rapidly and the shear stress peak point moves to the anchorage free end. The anchorage structure moves integrally along the macro-cracl~ The de-bonding stage is a research focus in the deformation and failure process of an anchorage structure, and plays an important guiding role in roadway support design and prediction of the stability of the surrounding rock.

Critical interfaces in geosynthetic multilayer liner system of a landfill

This study is to identify the critical interface in a geosynthetic multilayer liner system by examining the effects of the interface shear strength of liner components, leachate level, leachate buildup cases, and peak and residual interface strengths. According to current landfill design procedures, conducting stability analysis along the same interface at both the back slope and base may result in a non-conservative result. The critical interfaces with the minimum factor of safety are generally found at different locations along the back slope and base. The critical interface for a multilayer liner system cannot simply be assumed during stability analysis. It can shift from one interface to another with changes in the leachate level and with different leachate buildup cases. The factor of safety for an interface with a high friction angle and low apparent cohesion generally drops much more quickly than it does under inverse conditions when the leachate level increases. The failure interface in a liner system under residual conditions is usually different from the failure interface under peak conditions.

A Biomimetic Hip Joint Simulator and its Application in in vitro Study of the Integrity of Replacement Cemented Hip

A biomimetic hip joint simulator that can be used to evaluate the outcome of the cemented total hip replacement has been designed, manufactured and evaluated. The simulator produces motion in the extension/flexion plane, with a socket to rotate internal/externally. At the same time a dynamic loading cycle is applied. A validation test was performed on a cemented femoral stem within a novel composite femur. The hone quality has a strong effect on the stem migration and on the integrity of the interfaces. The migration of the stem is a combination of 3-D translation and rotation of the stem. Under the same loading conditions, weak bone allows more stem migration than strong bone. There is a great decrease in the strength of the stem-cement interface after the dynamic test, and the weak bone composite exhibited a greater reduction in interfacial strength than the strong bone composite. The decrease of the interfacial strength indicates that the primary bonding between the stem and the cement mantle had deteriorated and the integrity of stem-cement interface was damaged. The study demonstrates the value of using a hip joint simulator to investigate stem migration and interface integrity within the cemented hip replacement, suggesting that method can be used for in vitro evaluation of the biomaterials used in the cemented hip replacements.

A LOWER BOUND LIMIT ANALYSIS OF DUCTILE COMPOSITE MATERIALS

The plastic load-bearing capacity of ductile composites such as metal matrix composites is studied with an insight into the microstructures. The macroscopic strength of a composite is obtained by combining the homogenization theory with static limit analysis, where the temperature parameter method is used to construct the self-equilibrium stress field. An interface failure model is proposed to account for the effects of the interface on the failure of composites. The static limit analysis with the finite-element method is then formulated as a constrained nonlinear programming problem, which is solved by the Sequential Quadratic Programming （SQP） method. Finally, the macroscopic transverse strength of perforated materials, the macroscopic transverse and off-axis strength of fiber-reinforced composites are obtained through numerical calculation. The computational results are in good agreement with the experimental data.

An interfacial mechanical model for the analysis of earthquake

In this paper, the shear beam model for analysis of interface failure under joint action of anti-plane shearing and lateral compression and its principal behavior were briefly introduced. The calculation of energy release that is related to the strength of earthquake was presented by using the shear beam model. The sudden increase of load resulted from the 'stress locking' at the interface layer in the reloading process was investigated. At the end of the paper, discussions on the mechanism of earthquake were given out.

Micromechanical Behavior and Failure Mechanism of F / B Multi-phase High Performance Steel

The deformation and micro-voids formation mechanisms in ferrite / bainite（ F / B） multi-phase steel with the volume fraction of bainite less than 50% were studied by numerical simulation and experimental observation. The results show that the micro-strain concentrates at the soft / hard phase（ F / B） interface in the multi-phase steel,which should be correlated with the mechanism of incoordinate deformation. During the necking of the steel,the micro-voids initially form around the F / B interface,which also form in ferrite and bainite with the severe strain. The micro-voids in bainite are more dense and finer than those in ferrite. The failure mechanism of bainite is the coalescence of micro-voids,and the failure mechanism of ferrite is the growth and tearing of micro-voids. Due to the different failure mechanisms of ferrite and bainite,a suitable part of soft phase would be beneficial to the capability of anti-failure of F / B multi-phase steel during the ductile fracture.