Effect Of Interfacial Shear Strength Research Articles

Study on reasonable anchorage length based on failure mechanism of the bolt anchorage system

In addition to analysing the mechanism of failure of the prestressed rock anchor anchor system and investigating the appropriate depth for fixing the rock anchors, theoretical equations were derived to calculate the rock anchors' axial force, ultimate capacity, and the interfacial shear force in the elastic phase. These equations are then used to analyse the pressure distribution within the rock bolt anchorage section and to investigate the effect of interfacial shear strength, shear stiffness, and anchorage length on interface failure. Drawing on the findings from both field-based rock bolt pull-out tests and numerical simulations, analyzed the failure mechanism of the anchor system, and proposed a reasonable anchor length design method for rock bolt. The results show that there is a strong dependence between ultimate load carrying capability of rock bolts and interfacial shear stress and shear rigidity, and that increasing the anchorage length and reducing the interface shear stiffness can avoid the stress concentration phenomenon. The primary factor leading to the anchor system failure is secondary interface failure. The evolution law of interface damage is that the damage occurs first at the initial position. As the interface damage location changes, the peak shearing stress moves towards the bottom of the anchored section. The engineering application results verified the feasibility of a reasonable anchorage length calculation method and rock bolt design process. The findings of this paper can be used as a basic reference for determining rock bolt anchorage support parameters during the design and construction of underground engineering projects.

Effect of interfacial shear strength between magnetic particles and carrier liquid on rheological properties of magnetorheological fluids

The interfacial mechanical strength between carbonyl iron particles (CIPs) and carrier liquid is one of the key factors for the rheological properties of magnetorheological (MR) fluids. Here, the microstructure and shear properties of the interface between CIPs and dimethyl silicone oil (DSO) are studied using molecular dynamics simulation. Results indicate that there is strong adhesive strength between Fe atoms on the surface of CIPs and DSO molecular chains during the shearing process. For the MR fluids with DSO viscosity of 50 and 200 mPa⋅s, the DSO molecular structure between CIPs is easy to break out under shear deformation owing to the short DSO chains. While as for the Fe/DSO/Fe model with DSO viscosity of 350 and 500 mPa⋅s, the interfacial shear strength is greatly higher than that with low viscosity DSO due to the entanglement between long chains of DSO. Finally, MR fluids with different viscosity DSO are prepared for rheological tests to verify our simulation results. By combining simulation and experiment, the high interfacial shear strength can improve the rheological properties of the MR fluids. These insights reveal the relationship between the interfacial shear properties of the CIPs/DSO and the rheological properties of MR fluids.

Effect of interface behaviour on damage and instability of PBX under combined tension–shear loading

To study the effect of interface behaviour on the mechanical properties and damage evolution of PBX under combined tension–shear loading, the present work establishes the numerical model of a PBX three-phase hybrid system, which introduces a nonlinear plastic damage cohesion model to study the mechanical response and damage process. The parameters in the model were fitted and calibrated. Taking the crack growth rate as the feature, the damage state in each stage was determined, and the damage instability criterion was given. The effects of interfacial tensile strength and shear strength on the damage process of PBX were studied. On this basis, serrated and hemispherical structures interface of PBX has been developed, which affects the damage process and instability during the loading process. The results indicate that damage state response of PBX experiences the process of stable load bearing, unstable propagation, and complete failure. At the critical moment of instability, the overall equivalent effective strain of material reaches 3024 με and instability loading displacement reaches 0.39 mm. The increase of interfacial tensile strength and shear strength significantly inhibits the damage of PBX. The effect of interfacial shear strength on critical instability of PBX is approximately 1.7 times that of the interfacial tensile strength. Further, interface opening along the normal direction is the main damage form at the interface. Serrated and hemispherical rough interfaces can significantly inhibit propagation of cracks, and the load bearing capacity is improved by 22% and 9.7%, respectively. Appropriate improvement of the roughness of the interface structure can effectively improve the mechanical properties. It is significantly important to have a better understanding of deformation, damage and failure mechanisms of PBX and to improve our predictive ability.

Effects of interfacial shear strength on the operative aspects of interphase section and tensile strength of carbon-nanotube-filled system: A modeling study

In this article, the required interfacial shear strength (τc) between a polymer medium and carbon nanotubes (CNTs) is determined to define the operative interphase thickness in nanocomposites. The roles of the operative interphase thickness in the operative CNT loading and percolation onset are determined. Additionally, “τc,” interfacial shear strength (τ), operative filler concentration, CNT curliness, interphase thickness, and percolation onset are used to develop a model for determining the strength of CNT-filled systems. The equations and the suggested model adequately reflect the roles of the parameters in the model’s outputs. In addition, many real values for several examples validate the proposed model. A low “τc” and high “τ” positively control the operative interphase thickness, operative CNT concentration, and percolation onset, thus improving the nanocomposite’s strength. Among the variables considered herein, CNT size is the most important term because it changes the relative strength (nanocomposite’s strength divided by polymer strength) from 1 to 25.

Shear Wave Propagation Across Filled Joints with the Effect of Interfacial Shear Strength

The thin-layer interface model for filled joints is extended to analyze shear wave propagation across filled rock joints when the interfacial shear strength between the filling material and the rocks is taken into account. During the wave propagation process, the two sides of the filled joint are welded with the adjacent rocks first and slide on each other when the shear stress on the joint is greater than the interfacial shear strength. By back analysis, the relation between the shear stress and the relative tangential deformation of the filled joints is obtained from the present approach, which is shown as a cycle parallelogram. Comparison between the present approach and the existing method based on the zero-thickness interface model indicates that the present approach is efficient to analyze shear wave propagation across rock joints with slippery behavior. The calculation results show that the slippery behavior of joints is related to the interfacial failure. In addition, the interaction between the shear stress wave and the two sides of the filling joint influences not only the wave propagation process but also the dynamic response of the filled joint.

Nonlinear Multi-Scale Finite Element Method to Predict Tensile Behavior of Carbon Nanotube-Reinforced Polymer Composites

The ability of carbon nanotubes (CNTs) to consider as the strongest and stiffest elements in nanoscale composites remains a powerful motivation for the research in this area. This paper describes a finite element (FE) approach for prediction of the mechanical behavior of polypropylene (PP) matrix reinforced with single walled carbon nanotubes (SWCNTs). A representative volume element is proposed for modeling the tensile behavior of aligned CNTs/PP composites. The CNT is modeled with solid elements. Modified Morse potential is used for simulating the mechanical properties of an isolated carbon nanotube. The matrix is modeled as a continuum medium by utilizing an appropriate nonlinear material model. A cohesive zone model is assumed between the nanotube and the matrix with perfect bonding until the interfacial shear stress exceeds the bonding strength. Using the representative volume element, a unidirectional CNT/PP composite was modeled and the results were compared with corresponding rule-of-mixtures predictions. The effect of interfacial shear strength on the tensile behavior of the nanocomposite was also studied. The influence of the SWCNT within the polymer is clearly illustrated and discussed. The results showed that polymer's Young's modulus and tensile strength increase significantly in the presence of carbon nanotubes.

The effect of interfacial shear strength on damping behavior of carbon nanotube reinforced composites

The effect of interfacial shear strength (ISS) on the mechanical and damping properties of carbon nanotube reinforced composites (CNT-RCs) is investigated in the present study using a multiscale simulation. The atomic lattice of CNTs is modeled with the modified molecular structural mechanics (MMSM) approach and reduced to an equivalent beam element (EBE) which is used as the basic building block for the construction of full length CNTs embedded in the polymer. Linear material properties are assigned to the EBEs, while a Maxwell–Wiechert material model is used for modeling the viscoelastic behavior of the polymer. The interfacial load transfer mechanism between the lateral surface of the carbon nanotube and the surrounding matrix is taken into account with a nonlinear bond-slip friction-type model. Finite element models of representative volume elements (RVEs) are constructed comprised of two independent meshes: a structured with solid elements for the matrix and a series of embedded EBEs for the full length CNTs inside the matrix. Straight as well as wavy CNTs are considered. In the case of wavy CNTs, random CNT geometries are generated using the spectral representation method with evolutionary power spectra (EPS) which are derived from processing scanning electron microscope (SEM) images. Stochastic average properties were derived with Monte Carlo simulation. The mechanical and damping properties of the CNT-RCs are assessed on the basis of sensitivity analyses with respect to various weight fractions and interfacial shear strength (ISS) values. Numerical results are presented, showing the significant effect of the ISS as well as the influence of CNT waviness on the damping behavior of CNT-RCs.

A multiscale approach for estimating the chirality effects in carbon nanotube reinforced composites

In this paper, the multiscale representative volume element approach is proposed for modeling the elastic behavior of carbon nanotubes reinforced composites. The representative volume element incorporates the continuum approach, while carbon nanotube characterizes the atomistic approach. Space frame structure similar to three dimensional beams and point masses are employed to simulate the discrete geometrical constitution of the single walled carbon nanotube. The covalent bonds between carbon atoms found in the hexagonal lattices are assigned elastic properties using beam elements. The point masses applied on each node are coinciding with the carbon atoms work as mass of beam elements. The matrix phase is modeled as a continuum medium using solid elements. These two regions are interconnected by interfacial zone using beam elements. Analysis of nanocomposites having single walled carbon nanotube with different chiralities is performed, using an atomistic finite element model based on a molecular structural mechanics approach. Using the proposed multi scale model, the deformations obtained from the simulations are used to predict the elastic and shear moduli of the nanocomposites. A significant enhancement in the stiffness of the nanocomposites is observed. The effects of interfacial shear strength, stiffness, tensile strength, chirality, length of carbon nanotube, material of matrix, types of representative volume elements and types of loading conditions on the mechanical behavior of the nanocomposites are estimated. The finite element results are compared with the rule of mixtures using formulae. It is found that the results offered by proposed model, are in close proximity with those obtained by the rule of mixtures.

Study on longitudinal tensile properties of SiCf/Ti–6Al–4V composites with different interfacial shear strength

Abstract Effect of interfacial shear strength on longitudinal tensile properties for SiC f /Ti–6Al–4V composites is investigated by Monte Carlo finite element method. A two-parameter Weibull function is employed to describe random distribution of fiber strength. Fiber breakage, matrix cracking and interfacial debonding are simulated by killing the element when stress applied to element exceeds corresponding strength and releasing coupled nodes when shear stress exceeds shear strength at interfaces. The results show that tensile strength of SiC f /Ti–6Al–4V composites keeps unchanged for various interfacial shear strengths, but low interfacial shear strength is advantageous to reduce catastrophic failure. Moreover, with low interfacial shear strength, fiber breakage in the composites is more inclined to be non-coplanar. In addition, tensile strength obtained from finite element method is compared with those predicted by global load-sharing model (GLS), local load-sharing model (LLS) and conventional rule of mixtures (ROM) and is identical with that obtained from LLS.

Multi-scale modeling of tensile behavior of carbon nanotube-reinforced composites

A multi-scale representative volume element (RVE) for modeling the tensile behavior of carbon nanotube-reinforced composites is proposed. The RVE integrates nanomechanics and continuum mechanics, thus bridging the length scales from the nano- through the mesoscale. A progressive fracture model based on the modified Morse interatomic potential is used for simulating the behavior of the isolated carbon nanotubes and the FE method for modeling the matrix and building the RVE. Between the nanotube and the matrix a perfect bonding is assumed until the interfacial shear stress exceeds the corresponding strength. Then, nanotube/matrix debonding is simulated by prohibiting load transfer in the debonded region. Using the RVE, a unidirectional nanotube/polymer composite was modeled and the results were compared with corresponding rule-of-mixtures predictions. A significant enhancement in the stiffness of the polymer owing to the adding of the nanotubes is predicted. The effect of interfacial shear strength on the tensile behavior of the nanocomposite was also studied. Stiffness is found to be unaffected while tensile strength to significantly decrease with decreasing the interfacial shear strength.

Effect of interfacial shear strength on the mechanical response of polycarbonate and PP reinforced with basalt fibers

The effect of shear strength of the interphase on the mechanical properties of polycarbonate (PC), isotactic polypropylene (PP) and ithaconic acid grafted polypropylene (ITAPP) reinforced with bare unidirectional basalt fibers (BF) was investigated in a dry state and after immersion in hot water. A single embedded fiber test was utilized to determine the average shear strength of the interphase, τ a, Four millimeters thick unidirectional fiber reinforced laminates were prepared by laying up eight 0.5 mm thick UD fiber reinforced PC, PP and ITAPP prepregs. Bare and PC oligomer grafted basalt fibers were utilized in PC based composites while only bare basalt fibers were used in PP and ITAPP based composites. Both model single fiber composites and UD laminates were exposed to 85°C water for 100 h followed by 100 h drying at 100°C in a vacuum oven. In the dry state, the shear strength of the interphase varied from 10 MPa for bare BF/PP to 40 MPa for bare BF/PC annealed at 245°C for 10 min. The τ a decreased after water exposure approximately 20% for all the model composites investigated, from 8 MPa for bare BF/PP to 33 MPa for bare BF/PC annealed at 245°C for 10 min. Longitudinal elastic modulus and dry transverse modulus were almost independent of the τ a, whereas the transverse modulus increased with the τ a by 75% after water exposure. On the other hand, both longitudinal and transverse strength of all the composites investigated increased with τ a by 50% and 100% respectively. In PC/bare BF and PP/bare BF, greatest reduction of mechanical properties upon water immersion was observed. PC/bare fiber composite annealed at 245°C for 10 min and PC with PC oligomer grafted fibers exhibited excellent retention of properties after long-term immersion in hot water. Similar results were found for ITAPP/bare GF. This finding was attributed to the formation of high modulus PC interphase relatively impermeable by water and by formation of stable chemical bond between surface hydroxyls on basalt fibers and carboxylic groups of the ITAPP.

Effect of IFSS on tensile strength of unidirectional fiber composites using 3D-FEM simulation

A Monte-Carlo simulation model based on 3D-finite element analysis was developed to clarify the effect of interfacial shear strength (IFSS) on tensile strength of a unidirectional composite with fibers placed in a hexagonal array. The simulation model comprises fiber, matrix and interface elements; thereby, fiber breaks, matrix fractures and interfacial debondings during loading can be predicted individually. Tensile fracture processes and strengths of a boron/epoxy composite were simulated at various IFSSs. Results show that as IFSS decreases, stress concentration factors to intact fibers adjacent to a broken fiber element decrease because of occurrences of interfacial debonding. However, since interfacial debonding also reduces load carrying capacity in broken fibers, composite strength is reduced in all fiber volume fractions. On the other hand, a large IFSS causes many matrix fractures at once; therefore, it induces low composite strength. Thus, intermediate IFSSs increase tensile strength of the composite. This means that there must be an 'optimum' IFSS which induces the highest tensile strength of the composite. The optimum value shifts to a low value as fiber volume fraction increases. This occurs because the matrix around broken fiber elements becomes more apt to be broken easily in shear at a higher fiber volume fraction, therefore enhancing normal stress on intact fibers.

Effect of interfacial shear strength on reliability of strength and fracture process of SiC–Al composite

A unidirectional SiC fibre reinforced pure aluminium composite was fabricated by the hot press method. Tensile testing of the SiC–Al was carried out to determine composite and interfacial shear strengths. A Monte Carlo procedure based on the elastic–plastic finite element method, involving the interfacial layer around the fibres, was constructed to simulate the tensile testing and to calculate the strength and Weibull parameters for the SiC–Al composite. The effect of the interfacial shear strength on the composite strength and its reliability is discussed. The results show that the composite strength and the Weibull shape parameter increase with increasing interfacial shear strength. The contribution of the interfacial shear strength to the composite strength and reliability is efficient when the interfacial shear strength is lower than the matrix shear strength. It is concluded that both composite strength and reliability are closely related to the fibre fracture process.

Effect of interfacial adhesion and statistical fiber strength on tensile strength of unidirectional glass fiber/epoxy composites. Part I: experiment results

Abstract The effects of fiber surface treatment on ultimate tensile strength (UTS) of unidirectional (UD) epoxy resin matrix composites are examined experimentally. The interfacial shear strength (IFSS) and statistical fiber strength are significantly altered by five different kinds of surface treatments, which are: (a) unsized and untreated; (b) γ-glycidoxypropyltrimethoxysilane (γ-GPS); (c) γ-methacryloxypropyltrimethoxysilane (γ-MPS); (d) mixture of γ-aminoxypropyltrimethoxysilane (γ-APS), film former (urethane) and lubricant (paraffin); and (e) urethane-sized. The maximum UTS is obtained for the relatively strong interfacial adhesion (glass/γ-MPS/epoxy) but not for the strongest interfacial adhesion (glass/γ-GPS/epoxy). The governing micro-damage mode around a broken fiber and the interface region is matrix cracking for γ-GPS treated fibers, and a combination of interfacial debonding and matrix cracking for γ-MPS treated fibers. The micro-damage mode related to the interfacial adhesion strongly affects the fracture process, and thus the UTS of UD composites. The results also indicate that the interfacial adhesion can be optimized for effective utilization of fiber strength for fiber composites. A parameter called “efficiency ratio” of fiber strength in UD composites is proposed to examine and distinguish different effects of IFSS and fiber strength on the UTS of UD composites. The experimental results show that improved UTS of UD composites due to surface treatments mainly result from the increase in fiber strength but not from the modified interface.

Effect of Interfacial Shear Strength on Impact Properties of Nb/MoSi<SUB>2</SUB> Laminate Composites

The relationship between the interfacial shear strength and the impact properties of Nb/MoSi 2 laminate composites have been investigated, in conjunction with the evaluation of their fracture strain and the thickness of interfacial reaction layer. Nb/MoSi 2 laminate composites have been fabricated by stacking sintered MoSi 2 sheets and Nb sheets, alternately and hot pressing in the griphite mould. The instrumented Charpy impact test, the interfacial shear test and the tensile test was carried out at the room temperature. To change the interfacial shear strength associated with the thickness of interfacial reaction layer, Nb/MoSi 2 laminate composites were fabricated as the parameter of hot press temperature. It is found that the interfacial shear strength between MoSi 2 and Nb increases with the growth of the interfacial reaction layer, which results from the increase of fabricating temperature. Such a increase of the interfacial shear strength leads to a localized deformation of Nb foil and then deteriorates the enhancement of impact value in Nb/MoSi 2 laminate composites. There is obviously an appropriate interfacial shear strength capable of maximizing the impact value in this composite system, associated with the plastic deformation of Nb foil.

The role of interfacial debonding in increasing the strength and reliability of unidirectional fibrous composites

A Monte-Carlo simulation technique based on a finite-element method has been developed in order to clarify the effect of interfacial shear strength on the tensile strength and reliability of fibrous composites. In the simulation a boron/epoxy monolayer composite was modelled, and five hundred simulations were carried out for various interfacial shear strengths. The interfacial shear strength value which raised the average strength of the composite corresponded approximately to the value which reduced the coefficient of variation. This implies the existence of an optimum value of interfacial shear strength which can increase the strength and reliability. The simulated strength and reliability were closely related to the degree and type of damage around a fiber break. That is to say, large-scale debonding caused by a weak interfacial bond and matrix cracking caused by a strong bond reduced the number of fiber breaks accumulated up to the maximum stress, and decreased the strength and reliability. On the other hand, small-scale debonding promoted comparatively the cumulative effect of fiber breaks and played a key role in increasing the composite strength and reliability.

The Effect of Interfacial Shear Strength on the Performance of Coated Surfaces in Repeated Sliding

When hard rough surfaces slide repeatedly on softer half-spaces, systems of protective residual stresses may be developed in the near surface layers of the softer material which enable loads sufficiently large to cause plastic deformation in the early cycles of loading to be accommodated purely elastically in the later stages of component life. This is the process of shakedown and limits on the intensity of the allowable Hertzian pressures consistent with the eventual cessation of plastic deformation for uniform half-spaces are now well established. In this paper, we produce shakedown maps for coated or treated surfaces, choosing principally to carry out the numerical calculations on a system which models the behavior of ceramic coatings on steel substrates. In addition to the relative hardnesses of coating and the substrate, important system parameters are shown to be the normalized thickness of the coating and the strength or integrity of the bond at the interface between the coating and substrate. It is quite possible for the production of a coating of less than the critical thickness, or one displaying poor adhesion, to reduce the shakedown performance to lower values than would be the case for an unprotected surface. Design curves are produced which illustrate how the improvement in shakedown performance of such coated surfaces varies with the normalized depth of coating and the strength of the interlayer bond.

Effect of Interfacial Shear Strength on Crack‐Fiber Interaction Behavior in Ceramic Matrix Composites

Zircon matrix composites uniaxially reinforced with SiC fibers were fabricated with different interfacial properties by changing the fiber coatings. The phenomenon of crack interaction with fibers and/or fiber coatings and its dependence on the interfacial properties were studied using a microindentation technique. The influence of the fiber orientation relative to the crack extension direction on the crack‐fiber interaction was also investigated. Crack deflection was observed at the fiber‐matrix interface in composites having low interfacial shear strength, and the crack deflection was mostly single‐sided, but double‐sided deflection was also observed. Crack penetration into the fiber occurred in composites with high values of the interfacial shear strength. These observations were in general agreement with the theoretical predictions of the crack deflection behavior based on the bimaterial interfaces in ceramic composites, but additional observations were made on crack deflection at multiple fiber‐matrix interfaces.

Illustration of stress/strain behavior and yarn fragmentation in a pseudo-hybrid composite system

To study the stress/strain behavior and the fragmentation of fibers in a hybrid composite in tensile loading, a model strand was constructed with cotton yarns as the low-elongation component and polyester yarns as the high-elongation component. The effect of interfacial shear strength on the performance of a hybrid composite was simulated by varying the twist multiplier of the strands. It was observed that a strand with a lower twist level was more likely to show a typical hybrid stress/strain behavior and a multi crack fragmentation pattern. The same was found for strands with the highest twist levels but with cotton contents between 22 and 33%.