Pin-loaded Hole Research Articles

Effects of ceramic fillers on failure loads and failure mechanisms of laminated composites with two-parallel pin-loaded holes

In this study, the failure load values and failure mechanisms of ceramic materials filled E-glass/epoxy laminated composite plates that have two-parallel circular holes, subjected to tension forces by two-parallel rigid pins, are investigated experimentally. The composite plates used in the pin tests were produced by using three different ceramic fillers, which are Silicon Carbide (SiC), Boron Carbide (B4C), and Aluminum Oxide (Al2O3). The weight fractions of ceramic fillers in each composite plate are 5%, 10%, and 15%. For evaluating the influence of joint geometry on failure loads and failure mechanisms, the edge distance-to-hole diameter ratio, different pin-hole diameters, and the ratio of the distance between the side edge of the sample and the center of pin-hole to the hole diameter were considered as geometric parameters. The results from the experimental tests revealed that adding ceramic fillers to the composites up to a certain ratio leads to a remarkable increment in the failure load values of the composites compared to the neat (0 wt.%) composites for all weight fractions. Further, the ultimate failure load values were obtained for composite plates filled with Al2O3 ceramics in 10% weight fractions.

Micromechanical approach to viscoelastic stress analysis of a pin-loaded hole in unidirectional laminated PMC

This paper aims to investigate the effect of viscoelastic behavior of polymer matrix of unidirectional fiber-reinforced laminated composite on stress distribution around the pin-loaded hole under tensile loading. The Laplace transform is used to prevent the integral form of matrix governing stress-strain relation. Applying a micromechanical model, all equilibrium equations for the fibers are written analytically in the Laplace domain. The numerical algorithm of Gaver–Stehfest is implemented, and the governing equations were solved at any given time to extract the concerned results in the time domain. The obtained results are validated against the Finite Element Method results obtained through ANSYS software. Moreover, a comparison of the results of this study at the time equal zero with elastic solutions of other references showed a good agreement. The results revealed that in the long term, the maximum tensile load in the intact fiber around the pinhole was enlarged and the tensile load in fibers far from the pinhole slightly was decreased. Moreover, the location of the maximum axial load that had occurred on pinhole edges was moved slightly toward the center over time.

Assessment of a numerical strategy for fatigue growth and shape evolution of a corner crack from a pin-loaded hole

The study investigates fatigue growth and shape evolution of a corner crack in a pin-loaded hole by means of three-dimensional FE analyses. The constraint factor/plasticity-induced crack closure strategy was tuned to reproduce experimentally measured crack front shapes. The study quantitatively determines the LEFM acceptability regions using elastic–plastic simulations. It also assesses the sensitivity of crack propagation and shape evolution to the stress distribution along the front, to the relationship between J-integral and stress intensity factor, and to changing propagation rates along different directions. The proposed approach produces very accurate results in terms of crack propagation rate and shape evolution.

Enhancement of the in-plane and pin-load bearing behavior of a quasi-isotropic carbon fiber/epoxy matrix multi-scale laminate by modifying the fiber-matrix interphase using graphene nanoplatelets

The present work examines the effect of incorporating two different concentrations, 0.1% and 0.25%, of silane-functionalized graphene nanoplatelets GnP-GPTMS onto the carbon fiber surface of a quasi-isotropic laminate with the aim to enhance both, the laminate in-plane and the bearing strength, in a pin-loaded joint. Delamination damage modes associated with high-stress gradients were also suppressed in the in-plane loaded laminates, significantly increasing load-carrying capability. The bearing strength of a pin-loaded hole is correlated to the tensile, compression, and shear properties. The results showed an improvement of 13.8% in tensile strength for the 0.1% GnP-GPTMS concentration, as well as 17.3% for compressive strength, while for shear strength, the improvement was 11.89% for the laminate. On the other hand, the behavior of the material in the pin-loaded joint showed an increase of 10.83% for the bearing strength with the 0.1% GnP-GPTMS, fiber surface treatment. Distinct differences were noticed between the tensile stress-loaded area and the area of the residual impression of the pin in the failure mode between the only-resin treated carbon fiber composites and GnPs treated fibers. It was evident, that the interfacial shear strength (IFSS) played an important role on the failure mode. In the compression area in the pin-loaded region, there was a marked presence of a permanent deformation in the matrix. With a closer look at the local failure phenomena at the compression loaded area, there was no fiber kinking and the degree of matrix plasticity disappeared according to the level of interfacial adhesion.

About calculations of composite plate tensile failure in cross-section with bolt hole of single-shear bolted joint

Background. Bolted joints (BJ) are the main type of detachable connection. When designing the BJ with plates of layered composite material, there is a problem of calculating the BJ strength, in particular, the cross-sections weakened by the bolt hole. It is due to the complex nature of the interaction of the layers of the composite plate with each other and also with bolts, as well as the presence of a number of structural and technological parameters of the connection.Objective. The main task of this research is to find the functions of influence of the magnitude of the bolt / hole gap, also structure and secondary bending of the bolt and plate on the value of the generalized stress concentration coefficient (SCC) in the cross-sections with bolt hole of the layered carbon fiber reinforced plastic (CFRP) plate using the results of BJ numerical simulation.Methods. It was used a method of finite-elements and the 3D contact model as much as possible approached to real geometry and conditions of load application. Earlier, the authors created 24 3D models of samples of single-shear two-row bolted joint with CFRP (contact task), in which the structures of CFRP (6 variants) varied, as well as the bolt / hole gap (4 values). The magnitudes of bolt tightening force and the force that stretched the sample were unchanged. Based on the results of calculations, stress distributions were determined and values of SCC in CFRP plates in the bolt holes (tables, graphs) were obtained.Results. Based on these results and additional calculations, the following conclusions were reached:in the static calculation of composite plate tensile failure in cross-section with hole of single-shear bolted joint the upper value estimate of the theoretical SCC in the pin-loaded hole in the plate of orthotropic material can be obtained in accordance with the formula arising from the solution of EHS (Echavarrı’a, C., Haller, P. and Salenikovich, A).in order to obtain a generalized SCC , which additionally takes into account a number of factors of BJ with CFRP, the upper value estimate of the theoretical SCC must be multiplied by next factors:function of influence of the bolt / hole gap, structure and the secondary bending of the CFRP plate; - taking into account the interplay of CFRP layers. For the considered BJ with CFRP an evaluation was obtained ;Conclusions. There is an easy-to-use formula for the upper estimation of SCC in a pin-loaded bolt-hole in an orthotropic material plate. The functions of influence of the bolt / hole gap, structure, and bending of the CFRP plate at first approximation are linear. The refined value of the correction factor, which takes into account the interplay of the layers of the CFRP, should be obtained in additional experiments (physical or numerical).

Stress concentration around of pin-loaded hole in unidirectional multi-layered metallic matrix composite material

The objective of this study is to examine the stress concentration factor around a pin-loaded hole in a metallic matrix composite material, analytically and numerically. It is assumed that all unidirectional fibers lie in the metallic matrix while the shear stress in fibers is discarded. To generally derive the equilibrium equation for all fibers and the metallic matrix, the previous shear-lag theory had been improved and the extension in the metallic matrix was considered. Afterwards, the equilibrium equation was solved by the eigenvalue method while the displacement field and stress distribution around the pin-loaded hole were computed. Having calculated stress concentration factors and the displacement field in a unidirectional multi-layered composite material, we compared the analytical results with those numerical values from other references. Additionally, the effect of the pin’s diameter, as well as the edge-hole distance on maximum stress concentration factor was investigated. To recapitulate, it is seen that the modified shear-lag theory can simulate the mechanism of the load transfer between metallic matrices.

The effect of Al2O3 nano additions on failure of GFRP plate with two parallel pin loaded holes

The aim of this study is to scrutinize the effect of nano-additions on failure modes and loads of glass-epoxy laminate subjected two parallel pin-loaded holes, experimentally and numerically. Furthermore, the effect of physical and geometrical parameters such as the ratio of free edge distance of laminated composite to holes diameter (e/d) and the ratio of centre to centre distances of holes to holes diameter (M/d) have been investigated. Afterwards, to exactly prognosticate failure modes and the ultimate load obtained from the experimental procedure, a numerical simulation in finite element software was implemented. There have found a close agreement between two methods. It should be acknowledged that after augmenting glass-epoxy laminate with nano-addition A12O3, there was seen to be a clear difference between the two samples while the bearing strength of reinforced samples has been improved.

An analytical approach to predict the mechanical behavior of single-lap single-bolt composite joints reinforced with carbon nanofibers

In the present research, the stiffness and the damage initiation load of single-lap composite bolted joints (SLJs) reinforced with carbon nanofibers (CNFs) were studied. To this end, an analytical approach was developed and in the first step, the spring-mass model was modified. By having the elastic properties of the fiber, matrix and nano reinforcement, layup and geometrical parameters of the joint and using the modified spring-mass model, the stiffness of the joint was predicted. Then, by calculating the modulus and the stress concentration factor of a unidirectional ply with a pin-loaded hole and using the maximum stress failure criteria, the damage initiation load of the joint was predicted. Two different SLJs with [−45/0/+45/90]s and [90/−452/+45]s layups with and without nanoparticles were studied. The present analytical approach was evaluated by the finite element model as well as conducting an experimental program.

Failure analysis of unidirectional polymeric matrix composites with two serial pin loaded-holes

The objective of this study is to investigate the effects of geometrical and physical parameters on failure modes and failure loads in unidirectional polymeric matrix composites with two serial pin loaded holes, analytically and experimentally. It is assumed that all of unidirectional fibers in the laminate lie in one direction while loaded by a load p 0 at infinity, parallel to the direction of the fibers. To derive equilibrium equations based on a Shear-Lag theory, a rectangular arrangement of fibers is considered and with the proper use of boundary and boundness conditions, stress and displacement fields are computed within the laminate, along with the surrounding pinholes. Finally by using the Hashin criterion failure modes and failure loads are estimated. To validate analytical results based on shear-lag theory, an experimental program is carried out. A very good agreement is observed between two procedures. Based on results, in small sizes of two pins, the dominant failure mode is bearing and with the increasing of hole sizes, failure modes are changed to tension and shear modes.

Stress-Distribution around Pin-Loaded Hole for Orthotropic Laminates

Stresses were calculated for orthotropic laminate plate loaded by a frictionless pin in a circular hole of the same diameter. These calculations were based on finite-element analysis for five laminates; 00, [±450]s, [00/900]s,[00/±450]s, and quasi-isotropic [00/±450/900]s. stress distribution, based on nominal bearing stress, were determined for wide ranges of the ratios of width to diameter and edge distance to diameter. Orthotropic had a significant influence on both the magnitude and location of the maximum tensile stress concentration on the boundary of the hole. The laminates with 00 plies developed the peak tensile stress near the ends of the pin-hole contact arc. But the ±450 laminates had peaks where ply fiber were tangent to the hole. The finite width and edge distances strongly influenced the tensile stress concentration. In contrast, the finite widths and edge distances had little effect on bearing stress concentration. For the practical range w/d = 2, the peak tensile stresses were as much as 50 percent larger than the infinite-laminate value. For e/d=1, these stresses were greater 60 percent than infinite-laminate value. In contrast, the finite width and edge distance had little effect on bearing stress concentrations.

Investigation on characteristic length testing methods for failure prediction of composite multi-bolt joints

Characteristic lengths (CLs) are key factors in the characteristic curve method (CCM), which is widely used in engineering to predict the failure of composite multi-bolt joints. They directly affect the accuracy of predicting the joint failure. To identify suitable CL testing methods, six schemes have been designed and tested, in which two tensile CL specimens (open- and filled-hole laminates) and three compressive CL specimens (semi-circular notch laminates, pin-loaded hole laminates and single-bolt joints) have been compiled. Additionally, 3D FE analyses on the stress concentration have been performed and a discussion of the unit failure index curves of different specimens has been carried out to explore their load-carrying mechanism and determine why they result in different CLs. Failure predictions of composite multi-bolt joints by using the CCM with different CL testing schemes have been compared and evaluated using related static tensile experimental results. Filled-hole laminates for the tensile CL and single-bolt joints for the compressive CL are recommended because they best approximate the actual structure and obtain accurate failure predictions for composite multi-bolt joints.

The Mechanical Behavior of a Pin-Loaded Hole in a Thermoplastic Composite Laminate

The paper deals with the structural response of mechanically fastened fiber-reinforced laminated thermoplastic composite joints. An experimental investigation was carried out to analyze the behavior of single-pinned joints made with woven glass-reinforced polypropylene composite laminates. A detailed experimental analysis was performed in order to predict the bearing response, failure strength, and failure mode of composite laminates containing a pin-loaded hole. The results obtained allow one to evaluate the influence of geometric parameters and the stacking sequence of laminates on the behavior of such joints.

Analytical Study of a Pin-Loaded Hole in Unidirectional Laminated Composites With Triangular and Circular Fibers.

The problem of stress concentrations in the vicinity of pin-loaded holes is of particular importance in the design of multilayered composite structures made of triangular or circular glass fibers. It is assumed that all of the fibers in the laminate lie in one direction while loaded by a force p0 at infinity, parallel to the direction of the fibers. According to the shear lag model, equilibrium equations are derived for both types of fibers. A rectangular arrangement is postulated in either case. Upon the proper use of boundary and bondness conditions, stress fields are derived within the laminate, along with the surrounding pinhole. The analytical results are compared to those of the finite element values. A very good agreement is observed between the two methods. According to the results, composite structures made of triangular glass fibers result in lower values of stress concentrations around the pin, as opposed to those of circular glass fibers.

Analytical Study of Two Pin-Loaded Holes in Unidirectional Fiber-Reinforced Composites.

The objective of this paper is to investigate the effects of geometrical parameters such as the edge distance-to-hole diameter ratio {e/d}, plate width-to-hole diameter ratio {w/d}, and the distance between two holes-to-hole diameter ratio {l/d} on stress distribution in a unidirectional composite laminate with two serial pin-loaded holes, analytically and numerically. It is assumed that all short and long fibers lie in one direction while loaded by a force po at infinity. To derive differential equations based on a shear lag model, a hexagonal fiber-array model is considered. The resulting pin loads on composite plate are modeled through a series of spring elements accounting for pin elasticity. The analytical solutions are, moreover, compared with the detailed 3D finite element values. A close match is observed between the two methods. The presence of the pins on shear stress distribution in the laminate is also examined for various pin diameters.

The Damage Behaviour of Composite Tube with Pin Joint Holes

The present investigation deals with the damage behavior of composite tube with pinned-joint holes made by filament winding technique. The pin-loaded holes are tailored to fail mainly with bearing mode. The main objective of the paper is to investigate the stress state and damage behavior of pin-loaded holes made by filament winding. The failure load and the failure mode are analyzed numerically and experimentally. A good agreement between experimental results and numerical predictions is obtained.

Computation Method in Failure Analysis of Mechanically Fastened Joints at Layered Composites

This paper considers a computation method in failure analysis of layered composites containing pin-loaded holes. The investigation is focused on developing a reliable computation procedure to analyze initial failure load for pin-loaded holes at layered composite structures. Finite element method (FEM) is used to determine stress distribution around the fastener hole. Combining Chang-Scott-Springer characteristic curve model and Tsai-Wu initial failure criterion are used to determine joint failure. Special attention in this work is paid to pin-load distributions and its effect on the load level of failure and its location. In previous work initial failure analysis was carried out using cosine distribution between pin/lug mechanically fastened joint. Here contact finite element pin/lug model is analysed. The influence of stacking sequences of layered composites containing pin-loaded holes is also investigated. Special attention is paid to failure load and mode analyses in composites with stacking sequence [0/(±45)3/903]S. The computation results are compared with available experimental results. Good correlations between computation and experimental results are obtained.

Influence of material and geometrical parameters on stress field of composite plates with insert

Reduction of stress concentrations in the area of pin-loaded holes is one of the greatest challenges in the design of multilayered fibre-reinforced composite structures. Among many approaches to decrease concentration effects, putting metallic inserts in the holes is a convenient method. In this research, finite element analysis is applied to assess the effects of manufacturing parameters on stress concentration in the vicinity of the holes in composite plates with inserts. Edge and pitch distance, thickness and materials of insert, clearance between insert and composite part, and stiffness of the adhesive filling the gap are studied in this article. Investigations show that the optimum ratio of edge distance of insert to hole’s diameter is between 2 and 3. Results also show that the changes of the ratio of hole diameter to the width of plate do not have a considerable effect on the bearing concentration factor. Thicker insert reduces stress on the hole contour and higher clearance increases stress near the holes. Finally, increase of adhesive stiffness reduces the stress concentration caused by the clearance.

Modelling delamination onset and growth in pin loaded composite laminates

A three-dimensional (3D) finite element (FE) model is created with cohesive zone elements (CZE) to simulate a mechanically fastened [0°/90°]s pin-loaded joint in a composite laminate. The model incorporates fully integrated solid elements in the pin-loaded area to accurately capture the high stress gradients. Contact based cohesive elements with a bilinear traction–separation law are inserted between the layers to capture the onset and growth of delamination. The stress distribution around the pin-loaded hole was verified with the widely used cosine stress distribution model. Results from the FE model show that delamination damage initiated at the point of maximum average shear stress at the 0°/90° interface. The delaminated area develops an elliptical shape which grows in a non-self similar manner with increasing pin displacement. It is concluded that a progressive damage model should be included to provide a full understanding of the failure sequence, work that the authors are currently engaged with.

Structural analysis of composite bolted joints using the complex potential method

Abstract The problem of a pin-loaded hole in a symmetric composite plate with finite dimensions is considered within the scope of the classical laminate theory. The analysis is performed by means of the Lekhnitskii complex potential method. For the given problem, an appropriate power series expansion of the complex potentials is stipulated, where the coefficients are determined from the underlying boundary conditions. The present approach provides an efficient method for the calculation of stresses and displacements in the neighbourhood of the hole where failure is likely to occur.

Elastic-Plastic Stress Analysis of Cold-Worked Pin-Loaded Holes

Abstract A detailed two-dimensional, elastic-plastic finite element analysis of a pin-loaded hole was conducted. A thin rectangular aluminum alloy sheet (7075-T6) with a circular hole was considered under plane stress conditions. The hole was loaded purely by a rigid pin to different load magnitudes. Appropriate contact elements were used at the pin-hole interface to transfer the traction loads from one surface to another. Material nonlinearities for the sheet and friction were included in the analyses. Radial and hoop stress solutions along the pin-hole interface were compared in elastically and plastically loaded holes. The influence of friction on the stress results was studied. The locations and magnitudes of the peak hoop stresses were determined. Lastly, an initial residual field was introduced around the hole by a cold expansion simulation before a subsequent pin-loading analysis. Because the cold expansion process involves some reverse yielding, both isotropic and kinematic material hardening models were considered.