Shear Failure Surface Research Articles

Compaction mechanics of plastically deformable dry granules

To improve the understanding of how dry granulation and in particular, granule solid fraction (SF) impact the compaction behavior of plastically deformable microcrystalline cellulose (MCC), in this study, the Drucker Prager Cap (DPC) model parameters were calibrated using monodisperse MCC dry granules as model granules. Dry granules were produced as directly compressed small cylindrical compacts of MCC with SF in the range of 0.40 to 0.70 which were monodisperse in both size and SF. Virgin MCC powder and granules were compressed into tablets with SF in the range of 0.70 to 0.90. The DPC parameters (cohesion, internal friction angle, cap eccentricity, and hydrostatic yield stress), Young's modulus and Poisson's ratio were experimentally determined from diametrical and uniaxial compression, and in-die compaction tests. Results showed that calibration of the shear failure surface only may be adequate for MCC granules when the DPC model is completely calibrated for virgin MCC. Increasing granule SF significantly decreased the cohesion only. All other parameters were impacted by the tablet SF only. In the 2D yield surface, only the shear failure surface expanded as the granule SF increased. MCC of any granulation status requires the same in-die compaction stress state for densification to a given tablet solid fraction.

Ultimate strength behavior of curved steel–concrete–steel sandwich composite beams

A concept of using curved steel–concrete–steel (SCS) sandwich structure as the ice-resistant wall has been proposed for Arctic oil and gas drilling platform. In the developed curved SCS sandwich structure, ultra-lightweight cement composite (ULCC) and overlapped headed studs were used as the core material and bonding measures at the steel-concrete interface, respectively. In this paper, quasi-static tests on ten curved SCS sandwich beams have been carried out to investigate their ultimate strength behaviors under patch loading that considers the critical local ice-contact pressure. The test results reported the failure mode and shear resistances of structures, studied the influences of thickness of the steel skin shell, curvature, spacing of the connectors, depth of the cross section, strength of core materials, and boundary conditions on the ultimate strength behavior of the curved SCS sandwich beam. Extensive discussions and analysis were also carried out to provide information for the development of the analytical models. Analytical models were developed through modifying design code provisions. These innovative modifications in the analytical models included redefining the inclination angle of shear failure surface, redefining the effective depth of the section, considering the influence of the thickness of steel skin, and developing analytical models on tensile resistance of the overlapped headed studs. The accuracy of the predictions by the analytical models was checked by the test data. All these efforts were made to provide better predictions on the shear resistance of the curved SCS sandwich beam.

DEM analyses of the whole failure process of shallow foundation in plate load test on dense sand

Shallow foundations are widely used in civil engineering practice, but the instability mechanism is still unclear yet. Previously, the Finite Element Method (FEM) was commonly used to analyze the failure process of shallow foundations, but it meets difficulty in properly simulating the whole failure process of shallow foundation on the strain-softening material. Hence, the Discrete Element Method (DEM) is employed in this paper to study the instability mechanism of the shallow foundation via numerical plate load test with focus on the microscopic features evolution during vertical loading. In the simulation, an amplified gravity was applied to a dense granular ground to reproduce a gravity stress state at a large scale. Then, a plate was put on the granular ground to simulate the plate load test. Deformation pattern, particle velocity and distribution of void ratio in the ground were examined to illustrate the microscopic features in the whole failure process of the granular ground. The results show that: 1) There are a marked peak value and a settlement softening branch in the stress-settlement relationship. 2) The grids close to the edge of the plate are peculiarly extended and twisted. 3) Four particle motion patterns were observed in the velocity fields and the percentage of each motion pattern changes during loading. 4) The void ratio field varies during loading, and the distinguishing interface tends to be similar to Terzaghi's shear failure surface.

Shearing Failure Visualization via Particle Tracking in Soft Clay Using a Transparent Soil

In situ undrained shear strength measurement devices such as the vane shear test, cone penetrometer, and full-flow penetrometers (e.g., T-bar and ball) have been increasingly used as a part of geotechnical site investigations for soft clay deposits. Previous attempts to visualize the shear failure surfaces on these devices included either significant disturbance of the soil sample (permeated with resin and thin-sectioning) or involved methods of shearing along a transparent surface creating boundary effects. This paper described the use of non-invasive testing procedures to determine the failure surface of several in situ shear strength measurement devices in a soft clay surrogate (LAPONITE RD, a trademark of BYK Additives and Instruments). A series of tests were performed using two sizes of rectangular miniature vanes, two types of full flow penetrometer tests (T-bar and ball), and a cone penetrometer in LAPONITE RD samples. Laser planes were used to illuminate particles in the transparent material during shearing. Particle tracking techniques were used to visualize the failure surfaces and flow mechanisms for each device. Experimental results were compared with theoretical and numerical simulations of the failure surfaces and flow characteristics by previous researchers. The present work contributed to the understanding of undrained shear strength testing devices by an in situ assessment of the evolution, geometry, and structure of the failure surfaces and full-flow mechanisms.

Behaviour of steel tube-reinforced concrete flat slab shearhead systems

A new shearhead system between a steel tubular column and a reinforced concrete flat slab has been developed. Compared with normal flat slab structure using reinforced concrete frames, this shearhead system allows thinner slab thickness, easier fabrication and shorter construction time. Two full-scale tests were conducted, one using a square steel tube and the other using a circular steel tube. The tests were simulated with the finite-element package Abaqus for validation of the numerical simulation model, which included load–displacement and load–strain curves, crack development and punching shear failure surfaces. A sensitivity study for the numerical model was carried out to examine the effects of different material properties and mesh sensitivity in order to select the most appropriate modelling parameters using Abaqus.

경량골재 콘크리트 바닥판의 펀칭전단강도의 실험적 평가

This paper investigates the punching shear strength of lightweight aggregate concrete (LWAC) slabs through a series of experimental study. Five full scale slabs were constructed using normal concrete and four different types of LWAC. Each lightweight aggregate (LWA) used in this study had different sources (clay, shale, or slate) and shapes (crushed or spherical shape). Based on the test results, the effect of the lightweight aggregates (LWA) on the punching shear behavior was investigated. From the test results, it was found that the punching shear failure surface of LWAC slab with spherical shape coarse aggregate was less inclined than that with crushed shape coarse aggregate, which resulted in an increase of the area of the shear failure surface. As a result, it leads to the increased punching shear strength of the slab. On the other hand, the failure surfaces of LWAC slab with crushed shape coarse aggregate and normal coarse aggregate were inclined similarly. Finally, the test results of this study were compared with the punching shear strength obtained from current design models, such as ACI and CEB-FIP, to examine the validation of current design model to predict the punching shear strength of the LWAC slab.

Influence of the longitudinal reinforcement on the shear strength of one-way concrete slabs

The shear strength of one-way slabs is studied in this paper via an experimental program performed by the authors and the analysis of a shear test database. The experimental program, in which six slabs and three beams divided into two series were tested, was developed to study the influence of the slab width, the longitudinal reinforcement spacing and the bottom transverse reinforcement on the shear response of one-way slabs. The results showed that the width and the bottom transverse reinforcement do not significantly affect the shear response of the slab. The shear failure surface depends on the longitudinal reinforcement spacing because a three-dimensional resisting mechanism formed as a result of large bar spacing. A database of 79 tests on slabs was analysed to study in depth the influence of these parameters on the shear strength of one-way slabs. Finally, different shear procedures were applied to the database to evaluate their reliability to predict the shear strength.

Fractography of shear failure surface of softwood decayed by brown-rot fungus

In order to investigate shear failure surface of decayed wood, wood pieces of ezomatsu (Picea jezoensis) were exposed to brown-rot fungus (Fomitopsis palustris), and standard shear test in radial plane was conducted. The failure surfaces were examined by scanning electron microscopy and surface roughness measurements were also conducted. Transwall failure that the crack elongated parallel to the tracheid axis was observed in the earlywood region through all phases of decay. Intrawall failure principally occurred in the latewood region on the early phase of decay. When decay progressed considerably, transwall failure that the crack elongated perpendicularly to the tracheid axis occurred. And transwall failure was also dominant failure morphology in the latewood region. Fragments of tracheids which were partly peeled out from S2 layers were observed in some specimens. Size and appearance frequency of fragments of tracheid were smaller and lower when decay progressed. Arithmetic average roughness, which was the index of fragment size and appearance frequency, had positive correlation to shear strength ratio. Especially, line surface roughness of radial direction, which was measured across the radial files of tracheid, had the highest correlation to the shear strength ratio. The surface roughness would be a good indicator to evaluate the decay degree.

Stability assessment of Jinlong village landslide, Sichuan

The Jinlong village landslide is located in Zitong County, Sichuan and approximately 150 km east of Wenchuan. The landslide has exhibited creep deformation for nearly 30 years. Field investigations indicated that the slope deformation was caused by the combined effects of unfavorable topographic and geological conditions and earthquakes. The sliding surface is along a contact between silty clay and mudstone. The Wenchuan earthquake accelerated the creep, causing bulging of the ground surface. Shear test results of the silty clay near the sliding surface indicated that the residual strength is consistent with the stability state of the landslide. The factors of safety were calculated using the limit equilibrium method (LEM) and the method of fast Lagrangian analysis of continua in two dimensions. The results using the LEM indicate that the stability is clearly affected by seismic shaking, and when the peak ground acceleration is 0.08g, the slope reaches the limit state. The shear failure surface given by numerical simulation develops on the contact between the clay and silty mudstone, which confirmed the assumed sliding surfaces’ location using the LEM.

Failure patterns of geomaterials with block-in-matrix texture: experimental and numerical evaluation

In nature, due to complex geological process, some geomaterials with block-in-matrix texture exist that characterized by a heterogeneous structure including rock blocks embedded in a small-grained matrix. In literature, these materials also referred as bimrock (block-in-matrix rock). Typical examples of these complex materials are conglomerates, breccias, glacial till, coarse-grained alluviums, and melanges formations. When dealing with these complex media in engineering, it is important to understand the process by which the geomaterials fail under common loading conditions. In this paper, artificial bimrock specimens were prepared for different percentage of rock block proportions. The failure mechanism under uniaxial compression and indirect tension loading were studied. In order to compare the failure modes with homogeneous specimens, a numerical simulation of laboratory tests including uniaxial compression and Brazilian test was conducted on a typical bimrock and a homogenous specimen. The results showed different features of failure pattern for bimrocks with high proportions of rock blocks in comparison with homogeneous specimens. According to the experimental results, three main features were observed including a continuous tortuous failure surface, multiple localized shear failure surfaces, and detachment of rock blocks from the periphery of specimens.

Analytical study of steel bolt profile and its influence on bolt load transfer

The load transfer capacity of fully grouted steel bolts has been the subject of research for the past three decades. Experimental studies have confirmed that the bolt surface profile plays an important role in load transfer of fully grouted rock bolting systems. This research work seeks to lay the foundation for the role of the bolt profile in rock bolting mechanisms. A shear failure surface which is parallel to the bolt surface has been assumed and investigated using stress analysis. The stress field within the resin introduced by the axial load of the bolt has been formulated based on the half space theory, and the influence of the bolt profile configuration on rock bolting failure is identified under Mohr–Coulomb's failure criterion. Parametric studies show that bolts with smaller rib face angles or smaller profile height to length ratios are favourable to transfer load radially. Hence, they should be used in hard rock environments. On the contrary, bolts with large rib face angles and higher rib height to length ratios will transfer the major part of axial load into the resin in a direction parallel to the bolt surface. Thus, they should be used in soft rock conditions.

A New Apparatus for Evaluation of Contact Erosion at the Soil–Structure Interface

Abstract The interface between clay core-wall and concrete cut-off wall is one of the weakest parts of high earth and rockfill dams. An unsuitable design can cause contact erosion at the interface or shear failure surfaces, and eventually this will harm the safety of the dam. A new soil–structure contact erosion apparatus was developed for the evaluation of contact erosion at the interface under high stress, high hydraulic head, and large shear deformation. It consists of a soil–structure model base, a seepage pressure system, a confining pressure system, an axial pressure system, and a data acquisition system. The seepage pressure system simulates the seepage erosion effect at the interface, and the maximum seepage pressure is 2.0 MPa. The confining and axial pressure systems simulate the triaxial stress state of the interface and the large shear deformation of the soil structure; the maximum confining and axial pressures are 2.0 MPa and 4.0 MPa, respectively. The data acquisition system can monitor pore pressure dissipation and settlement. Two repeatable experiments on the interface between a kind of highly plastic clay and a concrete cut-off wall were conducted to verify the scientific utility of the new apparatus. The new apparatus was found to be capable of yielding fairly consistent results in repeatable experiments. The new apparatus will prove an effective tool for studying a reasonable connection form of concrete cut-off wall and core wall in high earth and rockfill dams.

SiC Die Attach Metallurgy and Processes for Applications up to 500 $^{\circ}{\rm C}$

The challenges of packaging SiC-based electronics for high-temperature applications include their high operating temperatures, wide thermal cycle ranges, and, sometimes, high currents and high voltages. As a result, the selection of metallurgy for high-temperature SiC die attach is crucial to a successful package design, which involves chip metallization, substrate metallization, and die attach alloy. This paper examines off-eutectic Au-Sn as the die attach alloy with a PtAu thick film metallization on AlN substrates. A pure Au thick film layer was printed over the PtAu thick film layer. AlN substrates metalized with refractory MoMn and electroplated Ni/Au were also used. Two different die attach approaches have been investigated, using Sn-Au-Sn off-eutectic thick foil and limited-volume eutectic AuSn (80/20 wt.%) preform. The SiC backside metallizations evaluated were Ti/TaSi2/Pt/Au and Cr/NiCr/Au. Die shear tests were performed after aging at 500°C and after thermal cycling. The shear test results and failure surface analysis are discussed.

Towards simulating built-up-edge formation in the machining of steel

Finite element simulations of the machining of carbon steels have been carried out over the cutting speed range 0.1–150 m/min. This range spans the ≈1–60 m/min within which built-up-edge occurs in practice. The material models used have included strain hardening varying with cutting speed. They have also included peaks in flow stress and reductions in ductility over temperature ranges associated with blue-brittle effects. The reductions in ductility have been introduced by means of a Johnson–Cook type of damage law which includes an influence of hydrostatic pressure on damage accumulation and a failure strain varying with temperature. The simulations are compared with previously published experimental results. They show that the damage law is more important than the thermal hardening associated with blue-brittleness in initiating built-up-edge formation. Secondary shear zone strain-rate fields have been obtained in which the surfaces of largest strain-rate are separated from the rake face by a stagnant region that may be considered to be an incipient built-up-edge. However, the variations of thrust force with cutting speed within the built-up-edge range that have been obtained from the simulations are not quantitatively realistic. In the modelling, material flow stress falls to zero once damage accumulation exceeds unity. It is speculated that a more realistic damage modelling, in which the shear failure surfaces between the chip and built-up-edge experience a residual friction resistance to slip between them, will lead to improved agreement with experiments. This will be investigated in future work.

Metallurgy for SiC Die Attach for Operation at 500°C

Metallurgy for high temperature SiC die attach involves the substrate metallization, die metallization, and die attach material. This paper examines off-eutectic Au-Sn as the die attach alloy with a PtAu thick film metallization on AlN substrates. A pure Au thick film layer was printed over the PtAu thick film layer. The SiC backside metallizations evaluated were Ti/TaSi/Pt/Au and Cr/NiCr/Au. Die shear tests were performed after aging at 500°C and after thermal cycling. The shear test results and failure surface analysis are discussed. Nanoparticle Ag and liquid transient phase bonding with Ag based metallurgies have been proposed for high temperature die attach. Data on the migration of sintered nano-particle Ag and thin film Ag dc bias during storage in air at 300°C and 375°C are presented. Migration of Ag is a potential failure mechanism for Ag based high temperature metallurgies.

Assessment of Shear Bond and Failure Surface of Bonded and Rebonded Brackets Using Conventional Acid and Micro-etching Techniques

Assessment of Shear Bond and Failure Surface of Bonded and Rebonded Brackets Using Conventional Acid and Micro-etching Techniques

Model test on sand retaining wall reinforced with denti-strip inclusions

In conventional reinforced soil structures, the reinforcements are often laid horizontally in the soil. In this paper, a new concept of soil reinforced with denti-strip inclusions was proposed and a series of laboratory model tests were carried out on sand retaining wall reinforced with denti-strip inclusions. Besides the horizontal displacements of the facing, the lateral earth pressures acting on vertical elements were measured. A microscopic measurement was performed to investigate the deformation and progressive failure of the sand within model retaining wall. Based on the image analytical technique, the bearing capability and interaction mechanism of reinforced sand retaining wall were analyzed. The model of the initial shear failure and potential failure surface were also put forward. From the experimental results, it is shown that denti-strip inclusions can increase the bearing capability of retaining wall significantly and restrict the facing displacements efficiently, as compared with conventional horizontal reinforcement.

Shear transfer between ribbed slab and edge column

The results of tests on six micro-concrete wide beam ribbed slabs at edge column locations are presented. It was found that punching shear failure of a wide beam ribbed slab can occur at an edge column. Although a punching shear failure of a wide beam ribbed slab is very similar to that of a solid slab, the shear capacity is reduced relatively, because some of the potential shear failure surface is lost when it enters the ribbed section. A plastic theory for punching shear was developed, which gave good agreement with the test failure loads.

Axial testing and numerical modeling of square shaft helical piles under compressive and tensile loading

Helical piles are increasingly used to support and rehabilitate structures subjected to both tensile and compressive axial loads. This paper presents a detailed investigation into the axial performance of helical piles. The study encompasses 19 full-scale load tests in different soils and numerical modeling using finite element analysis. The ultimate load criteria and load transfer mechanisms for helical piles were examined. In addition, the relationship between the installation effort (torque) and pile capacity was explored to determine its suitability for predicting pile capacity. The piles tested were made of three circular pitched bearing plates welded at a spacing of three helical diameters to a solid-square, slender steel shaft. It is proposed to determine the ultimate pile capacity as the load corresponding to pile head movement equal to 8% of the largest helix diameter plus the pile elastic deflection. A torque correlation factor, KT= 33 m–1for compression and KT= 24 m–1for uplift, was established to relate the ultimate pile capacity to the installation torque. It was found that load transfer to the soil is predominantly through a cylindrical shear failure surface that follows the tapered profile of the interhelices soils and the bearing capacity of the lead helix in the direction of loading.

Shear strength of R/C bridge cantilever slabs

This paper presents the results of six tests on R/C bridge cantilever slabs without shear reinforcement subjected to concentrated loading. The specimens represent actual deck slabs of box-girder bridges scaled 3/4. They were 10 m long with a clear cantilever equal to 2.78 m and with variable thickness (190 mm at the tip of the cantilever and 380 mm at the clamped edge). Reinforcement ratios for the specimens were equal to 0.78% and 0.60%. All tests failed in a brittle manner by development of a shear failure surface around the concentrated loads. The experimental results are investigated on the basis of linear elastic shear fields for the various tests. Taking advantage of the experimental and numerical results, practical recommendations for estimating the shear strength of R/C bridge cantilever slabs are proposed.