Interfacial Shear Cracks Research Articles

Limit Equilibrium of a Piecewise Homogeneous Plane with Small-Scale Interfacial Shear Cracks at a Corner Point in the Presence of a Loaded Internal Semi-Infinite Crack

Limit Equilibrium of a Piecewise Homogeneous Plane with Small-Scale Interfacial Shear Cracks at a Corner Point in the Presence of a Loaded Internal Semi-Infinite Crack

An experimental investigation on press joining mechanism and bearing behavior of single-lap composite riveted joints

This paper reports an experimental study on the forming mechanism and bearing behavior of single-lap composite riveted joints with different hole diameters (4.82 mm and 4.9 mm) and squeeze forces (15 KN, 18 KN, 20 KN, and 23 KN). Pressure riveting and tensile tests are conducted to composite riveted joints to obtain the joint interference, joint stiffness and bearing strength needed to quantitatively evaluate their deformation features and mechanical properties. Furthermore, microscopic studies on damaged areas using applying ultra-depth three-dimensional microscope to monitor damage evolution are conducted to comprehend the joint shear failure mechanism. Results show that the hole diameter and riveting force have a significant effect on the performance of the joint. The forming damage occurs mainly in the hole wall near the driven head and is dominated by fiber crushing and interfacial shear cracks. The radial expansion of the rivet shank is not uniform under the riveting force and the whole is drum shaped. But the hole expansion of the joint at 4.82 mm hole diameter is more uniform than 4.9 mm, which would lead to better joint stiffness and bearing strength. Moreover, high interference fit would cause the shear fracture of the rivet, while lower interference joints are dominated by compression-pull mixed failure. In general, the size of interference fit is an unneglectable factor in the composite riveted joints that should be thoroughly investigated.

Bond parameters for peeling and debonding in thin plated RC beams subjected to mixed mode loading – Framework

Studies have primarily focussed on predicting mode-II debonding failure; whereas, in real-case-scenario, flexurally strengthened reinforced concrete (RC) beams observe premature failure mechanisms under mixed-mode loading conditions engaging geometrical and material variations. Peeling is a consequence of flexural crack as debonding is of interfacial shear crack. Under bending, peeling failure is considerably catastrophic over debonding due to the nature of crack formation; therefore, this needs to be distinguished in predictive analysis. In this paper, a new numerical modeling methodology is approached using eXtended finite element method (xFEM) for flexural cracks and Cohesive Zone Model (CZM) for shear cracks without predefining crack locations. The parameters of the constitutive models are identified through comparing finite element results with the experimental data. These parameters are related to key material properties. Based on proposed framework, the models provide a good estimation of plate strain distribution, cracks and failure type, in terms of mode and load of failure. Bilinear bond-slip curve is a closer match over exponential crack evolution at interface.

Enhanced Digital Image Correlation Analysis of Ruptures with Enforced Traction Continuity Conditions Across Interfaces

Accurate measurements of displacements around opening or interfacial shear cracks (shear ruptures) are challenging when digital image correlation (DIC) is used to quantify strain and stress fields around such cracks. This study presents an algorithm to locally adjust the displacements computed by DIC near frictional interfaces of shear ruptures, in order for the local stress fields to satisfy the continuity of tractions across the interface. In the algorithm, the stresses near the interface are extrapolated by local polynomials that are constructed using a constrained inversion. This inversion is such that the traction continuity (TC) conditions are satisfied at the interface while simultaneously matching the displacements produced by the DIC solution at the pixels closest to the center of the subset, where the DIC fields are more accurate. We apply the algorithm to displacement fields of experimental shear ruptures obtained using a local DIC approach and show that the algorithm produces the desired continuous traction field across the interface. The experimental data are also used to examine the sensitivity of the algorithm against different geometrical parameters related to construction of the polynomials in order to avoid artifacts in the stress field.

Гранична рівновага кусково-однорідного пружного тіла з міжфазними зсувними тріщинами у кутовій точці межі поділу середовищ

Гранична рівновага кусково-однорідного пружного тіла з міжфазними зсувними тріщинами у кутовій точці межі поділу середовищ

Shear friction strength of monolithic concrete interfaces

This paper presents an integrated model for the shear friction strength of monolithic concrete interfaces derived from the upper-bound theorem of concrete plasticity. The model accounts for the effects of applied axial stresses and transverse reinforcement on the shear friction action at interfacial shear cracks. Simple equations are also developed to generalise the effectiveness factor for compression, the ratio of effective tensile to compressive strengths and the angle of concrete friction. The reliability of the proposed model is verified through comparisons with previous empirical equations and 103 push-off test specimens compiled from different sources in the literature. The previous equations considerably underestimate the concrete shear transfer capacity and the underestimation is notable for interfaces subjected to additional axial stresses. The proposed model provides superior accuracy in predicting the shear friction strength, resulting in a mean between experimental and predicted friction strengths of 0·97 and low scatter. Moreover, the proposed model shows consistent trends with the test results in evaluating the effects of various parameters on the shear friction strength.

Концентрация напряжений вблизи угловой точки границы раздела сред при наличии исходящих из нее маломасштабных межфазных сдвиговых трещин

Концентрация напряжений вблизи угловой точки границы раздела сред при наличии исходящих из нее маломасштабных межфазных сдвиговых трещин

Development of CFRE composite scarf adhesive joints with SiC and Al2O3 nanoparticle

The present work aims to strengthen scarf adhesive joints (SAJs) with 5° and 10° scarf angles in carbon fiber composite adherends via introducing SiC and Al2O3 nanoparticles into the adhesive epoxy. The SAJs were characterized under thermal and moisture environments. The ultimate tensile strengths (UTSs) of 5° and 10° SAJs were respectively improved by 41.2% and 8.4% for SiC/E-SAJs and 22.5% and 26.5% for Al2O3-SAJ compared to neat epoxy-SAJs. The UTSs and stiffness of the moist SAJs were marginally decreased. Although the UTSs of SAJs were decreased at 50°C, the strain at ultimate load and fracture toughness were tremendously increased and accordingly, the SAJs are not prone to sudden failure. Interfacial shear cracks were initiated between the adhesive layer and the stiffer-adherends at the joint-overlaps, whereas the adhesive layer remains attached to the lower stiffness adherend tip-ends. Crack initiation was detected effectively at about 65% of UTS of the SAJs using instrumented-SAJs with eight strain gauges. Applying such technique on composite structures can contribute in prolonging their service life by carrying out the necessarily repairs before the catastrophic failure of the structure. The experimental and predicted UTSs of SAJs using three-dimensional finite element analysis model are in good agreement, R2=0.9884.

An Analytical Model to Predict the Push-Out Capacity of Mortar from Rock Block

Ground anchors have been very practical in a wide range of geotechnical structures. Good bond properties at the anchor-mortar and mortar-rock interfaces can ensure transmitting an applied tensile load to a load bearing structure efficiently. The bond performance between the mortar and rock is necessary to be studied. A push-out test of mortar from rock block can be used to analyze the interfacial properties between the two materials. In this paper, an analytical model is proposed to determine the push-out capacity of mortar from rock block. Based on the deformation compatibility at the interface, the compressive stress in the mortar and the interfacial shear stress at the mortar-rock interface are formulated at different loading stages. By modeling interfacial debonding as an interfacial shear crack, the push-out load is then expressed as a function of the interfacial crack length. In virtue of the Lagrange Multiplier Method, the maximum push-out load is determined. The validity of the proposed model is verified with the experimental results. It can be concluded that if the interfacial parameters at the mortar-rock interface are obtained, the push-out capacity of mortar from rock block can be accurately determined using the proposed model. The proposed solution in this paper would provide a good theoretical basis in evaluating the stability of ground anchors in practice.

Analytical Solution for Fracture Analysis of CFRP Sheet–Strengthened Cracked Concrete Beams

Fiber-reinforced polymer (FRP) composite materials have been widely used in the field of retrofitting. Theoretical analysis of FRP plate- or sheet-strengthened cracked concrete beams is necessary for estimating service reliability of the structural members. In previous studies, the effect of a perfectly bonded FRP plate or sheet was equivalent to a cohesive force acting at the bottom of crack to delay the crack propagation in concrete and reduce the crack width. However, delamination between FRP and cracked beam is inevitable due to interfacial shear stress concentration at the bottom of crack. The intention of this paper is to present an analytical solution for fracture analysis of carbon FRP (CFRP) sheet–strengthened cracked concrete beams by considering both vertical crack propagation in concrete and interfacial debonding at CFRP-concrete interface. The interfacial debonding is modeled as the interfacial shear crack propagation in this paper. Four different stages are discussed after initial cracking state of the concrete. At the first stage, only fictitious crack propagation occurs in the concrete. At the second stage, macrocrack propagates in the concrete without interfacial debonding. At the third stage, both vertical macrocrack propagation in the concrete and horizontal shear crack propagation at the CFRP-concrete interface occur in the strengthened beam. The tensile stress in the CFRP sheet and interfacial shear stress along the span are formulated based on the deformation compatibility condition at the CFRP-concrete interface at this stage. Finally, macroshear crack propagates at the interface until the CFRP sheet is completely peeled out from the beam, and then the member is fractured. The applied load is determined as a function of the referred two crack lengths at different stages. At the beginning, the applied load increases to one peak value with the full propagation of fictitious crack at the first stage. At the third stage, the applied load is improved to another peak value due to the relatively high cohesive effect of the CFRP sheet. Then the two peak values are determined by the Lagrange multiplier method. The validity of the proposed analytical solution is verified with the experimental results and numerical simulations. It can be concluded that the proposed analytical solution can predict the load-bearing capacity of CFRP sheet-strengthened cracked concrete beams with reasonable accuracy.

Analytical solution for the pull-out response of FRP rods embedded in steel tubes filled with cement grout

Fiber-reinforced plastic (FRP) tendons have been widely used for ground anchors in civil engineering. Although various pull-out tests of FRP rods from grout-filled steel tubes have been conducted to simulate ground anchors in rock, there are relatively few theoretical studies reported in the literature for this type of bonded anchorages. The intention of this paper is to present an analytical solution for predicting the maximum pull-out load of FRP rods embedded in steel tubes filled with cement grout. First, the expression of the shear stress along the thickness direction of the grout layer is obtained analytically. The tensile stress in the rod and the interfacial shear stress at the rod–grout interface are formulated at different loading stages. By modeling interfacial debonding as an interfacial shear crack, the pull-out load is then expressed as a function of the interfacial crack length. Finally, based on the Lagrange multiplier method, the maximum pull-out load and the critical crack length are determined. The validity of the proposed analytical solution is verified with the experimental results obtained from literature. It can be concluded that the proposed analytical solution can predict the maximum pull-out load of spiral wound and indented rods embedded in steel tubes filled with cement grout with reasonable accuracy. The proposed solution can be also applied in predicting the pull-out capacity of steel bars from concrete.

Analytical Method for Failure of Anchor-Grout-Concrete Anchorage due to Concrete Cone Failure and Interfacial Debonding

Depending on the relevant material properties, failure of grouted anchor anchorage to concrete can result from pullout of concrete cones, debonding at either anchor-grout or grout-concrete interface, fracture of anchor, and combination of some of these failure modes. The intention of the present study is to present an analytical method for analyzing the concrete cone failure during the process of interfacial debonding by using deformation compatibility conditions at the anchor-grout and grout-concrete interfaces. The tensile stress in the anchor and interfacial stresses at the two interfaces are formulated at different loading stages. It is assumed that interfacial debonding modeled as an interfacial shear crack only appears at the anchor-grout interface and is initiated from the loaded end. The concrete cone and interfacial debonding failures are analyzed according to the sizes and material properties of the anchorage. Three different failure modes are considered, including concrete cone failure at the unloaded end without interfacial debonding, interfacial debonding plus concrete cone failure at the same height as the interfacial shear crack tip, and interfacial debonding plus concrete cone failure at the unloaded end. In each case, the load for the initiation of the concrete cone failure, and the cone angle are determined analytically. Subsequently, material and structural parameters are adopted to study their influences on the failure modes and calculated results. It is found that if the embedment length is relatively long, the concrete cone failure occurs within a local scope. If the concrete diameter is large enough, the failure mode is the interfacial debonding without concrete cone failure. The conclusions provide useful references for engineering practice such as designing grouted anchor anchorage to concrete in light of different needs and failure modes.

Nucleation of interfacial shear cracks in thin films on disordered substrates

We formulate a theoretical model of the shear failure of a thin film tethered to a rigidsubstrate. The interface between film and substrate is modeled as a cohesive layer withrandomly fluctuating shear strength/fracture energy. We demonstrate that, on scales largecompared with the film thickness, the internal shear stresses acting on the interface can beapproximated by a second-order gradient of the shear displacement across the interface.The model is used to study one-dimensional shear cracks, for which we evaluate thestress-dependent probability of nucleation of a critical crack. This is used to determine theinterfacial shear strength as a function of the film geometry and statistical properties of theinterface.