Shear-out Modes Research Articles

Connection Confinement of Bolted Fibre-Reinforced Polymer Bamboo Composite.

Parallel strand bamboo is a composite material that demonstrates high strength and low variability compared to other timber materials. However, its use in bolted connections is limited by a tendency to fail in shear-out mode. One promising technique to prevent failure is the method of confinement, whereby the composite connection is confined laterally, inducing a compressive force perpendicular to the composite fibres, which increases the shear strength in the loading process. This paper investigates the confinement method and its effect on parallel strand bamboo connections’ strength and failure mechanisms through experimental tests and ANSYS simulation methods. It was discovered that bolted connection confinement reduces the propensity of shear-out failure by counteracting shear stresses. A comparison of graphical results revealed that confinement increased the ultimate tensile capacity of parallel strand bamboo bolted connections by up to 26%. Confinement also improved the consistency of the connection’s mechanical properties throughout the loading process. These findings assist in refining and optimising practical applications of parallel strand bamboo connections by using the method of connection confinement.

ＣＦＲＰピン継手の疲労と準静的引張り負荷における強度と損傷進展の比較

A mechanically fastened joint in Carbon Fiber Reinforced Plastic (CFRP) laminates is necessary for its advantages in inspection, replacement and reliability, nevertheless its disadvantage in stress concentration. The mechanical joint should be designed to make the bearing failure mode occur because the strength is high and the joint fails non-catastrophically, while it fails catastrophically in other tensile and shear-out modes. In this study, the damage evolution of the pin joints for both [0/±45/90]3S and [90/±45/0]3S CFRP laminates and its difference between static and fatigue loading were discussed in detail. No difference between the macroscopic external appearance of damaged specimens under fatigue and static loading was observed, but the microscopic internal damage differed in critical damage and evolution. In static tests all the inside 0° layers had kinking at the maximum load and the kinking to be a trigger to the final failure with intense delamination and matrix crack. On the other hand, under fatigue loading the final damages mostly started from collapse at the loaded surface edge. It was also found that the total delamination length was longer in the case of fatigue at the same total matrix crack length and that [90/±45/0]3S presented higher strength than [0/±45/90]3S in both static and fatigue cases.

Behavior of Pin-loaded Laminated Composites

In this study, an investigation was carried out to determine the effects of joint geometry and fiber orientation on the failure strength and failure mode in a pinned joint laminated composite plate. Behavior of pin-loaded laminated composites with different stacking sequence and different dimensions has been observed experimentally. E/glass–epoxy composites were manufactured to fabricate the specimens. Mechanical properties of the composites were characterized under tension, compression and in-plane shear in static loading conditions. Laminated composites were loaded through pins. Single-hole pin-loaded specimens were tested for their tensile response and width-to-hole diameter (W/D) and edge distance-to-hole diameter (E/D) ratios evaluated. A series of experiments was performed with six different material configurations ([0/±45]s–[90/±45]s, [0/90/0]s–[90/0/90]s and [90/0]2s–[±45]2s), in all, over 120 specimens. E/D ratios and W/D ratios of plates were changed from 1 to 5 and 2 to 5, respectively. Failure propagation and failure type were observed on the specimens. The influence of the joint geometry on the strength of the pin-loaded composites was assessed. When laminated composite plates were loaded to final failure, three basic failure modes consisting of net-tension, shear out and bearing failure were observed for the different geometric dimensions. All the connections tested showed that the fiber orientations have a definite influence on the position around hole circumference at which failure initiated. Net-tension failure occurred for specimens that had small width and large end distance. When the width was increased, the specimens which had small end distances failed in the shear-out modes. When the end distance was increased, bearing failure developed in addition to shear-out failure. The experimental results showed that the ultimate load capacities of E/glass–epoxy laminate plates with pin connection were increased by increasing W and E. However, increasing the E/D and W/D ratios beyond a critical value has an insignificant effect on the ultimate load capacity of the connection.

Investigation of load bearing performances of pin connected carbon/polyphenylene sulphide composites under static loading conditions

The bearing strength of pin connections highly depends on joint and material parameters such as connection geometry, fibre orientation, layer orientation, pressure distribution along the plate thickness, etc. In order to investigate the bearing performance of the pin-loaded unidirectional carbon fiber reinforced polyphenylene sulphide (PPS) matrix composites, experiments have been carried out according to the ASTM D953 standards using Instron 4411. It is observed that pin loading performance has close relationship with fibre orientation of laminates and their deformation characteristics. Also the geometric parameters of end distance from the hole centre ( E) and width of the plate ( W) and pin diameter ( D) remarkably affect the load bearing performance of the materials. Joint failure with the net tension and shear-out modes is catastrophic and immediate. But bearing failure is progressive. Also fractoraphic investigations were performed to understand the deformations of the material with respect to the fiber orientations.

Mechanically fastened composite side-door impact beams for passenger cars designed for shear-out failure modes

The fuel efficiency and emission gas regulations of passenger cars are two important issues nowadays. The best way to increase the fuel efficiency without sacrificing safety is to employ fiber reinforced composite materials in the body of cars because fiber reinforced composite materials have higher specific strengths than those of conventional steel or aluminum. In this study, a composite side-door impact beam for passenger cars was designed to reduce the weight of steel impact beam using glass fiber reinforced composite. The static bending tests of the beams were performed for the optimum fiber stacking sequence, followed by the static tensile tests of the joint between the composite beam and the brackets on the car body. In order to increase the energy absorption characteristics of the composite impact beam, the mechanical joint was designed to fail with fiber shear-out mode, from which the impact energy might be dissipated during the side-door collision of passenger cars. The manufactured composite impact beam was mounted on the real side-door of a compact passenger car and tested under static bending moment. From the test, it was found that the composite impact beam with 70% weight of a high strength steel beam had comparable static bending strength.

A Progressive Damage Model for Mechanically Fastened Joints in Composite Laminates

A three-dimensional finite element model is developed to predict damage progression and strength of mechanically fastened joints in carbon fibre-reinforced plastics that fail in the bearing, tension and shear-out modes. The model is based on a three-dimensional finite element model, on a three-dimensional failure criterion and on a constitutive equation that takes into account the effects of damage on the material elastic properties. This is accomplished using internal state variables that are functions of the type of damage. This formulation is used together with a global failure criterion to predict the ultimate strength of the joint. Experimental results concerning damage progression, joint stiffness and strength are obtained and compared with the predictions. A good agreement between experimental results and numerical predictions is obtained.

Failure Mechanisms in Bolted CFRP

An experimental investigation on the damage mechanisms of mechanically fastened joints in composite laminates is presented. This information concerning damage mechanisms is required before developing damage progression models. For doublelap joints with fingertight washers, specimens that fail in the bearing, tension and shearout modes are investigated. For fully failed specimens and for specimens loaded to several percentages of failure load, the damage mechanisms are investigated using Xradiography and sectioning. It is concluded that failure occurs by a process of damage accumulation, where the failure mechanisms present are fiber fracture, delamination at the laminate loaded hole, matrix cracks and related fiber microbuckling, and internal delamination. Modelling this interaction between failure mechanisms requires further analytical efforts. Due to the importance of the through-thickness stresses present at the hole boundary, delamination has a significant effect on the joint strength, so the use of a threedimensional failure criterion is suggested.

Bolted joints of pultruded sandwich composite laminates

This paper describes the tensile behavior of bolted joints of pultruded sandwich composite laminates. The pultruded sandwich laminates have a skin-core-skin structure. Joint strength of longitudinal specimens was independent of specimen width ( w), whereas it increased with w in the case of transverse specimens. The joining efficiency of pultruded sandwich laminates was greater in the longitudinal direction than in the transverse direction. The core layer of longitudinal specimens failed by a combination of bearing and shear-out modes, independent of w. The failure mode of skin layers changed from net-tension to bearing mode with increasing w. In transverse specimens, the failure mode of core and skin layers changed from net-tension to bearing with increasing w. Finite element numerical analysis was carried out to predict the failure mode and joint strength. The numerical results were in good correlation with the experimental results.

Tensile Behaviour of Pultruded FRP Sandwich Composite Bolted Joints

In this experimental study, the tensile behaviour of bolted joints of pultruded glass fibre reinforced polyester sandwich composites was investigated. The transverse specimens cut normal to the pultrusion direction failed by net-tension whereas the longitudinal specimens cut parallel to the pultrusion direction failed by a combination of bearing and shear-out modes. The joint strength was dependent on the specimen geometry in the case of transverse specimens whereas it was not in the case of longitudinal specimens.

Post-Failure Analysis of Bolted Composite Joints in Tension or Shear-Out Mode Failure

A progressive damage model was developed for bolted joints in laminated composites which may fail in either tension mode or shear-out mode. The model is capable of assess ing damage accumulated in laminates with arbitrary ply orientations during mechanical loading and of predicting the ultimate strength of the joints which failed in tension or shear-out mode. The model consists of two parts, namely, the stress analysis and the failure analysis. Stresses and strains in laminates were analyzed on the basis of the theory of finite elasticity with the consideration of material and geometric nonlinearities. Damage accumulation in laminates was evaluated by the proposed failure criteria combined with a proposed property degradation model. Based on the model, a nonlinear finite element code was developed. Numerical results were compared with available experimental data. An excellent agreement was found between the analytical predictions and the experimental data.

Static Strength Prediction of Bolted Joint in Composite Material

A new method of predicting the strength of double shear single fastener composite joints is presented. The analysis method consists of calculating the stress distribution around a fastener hole using a finite exement analysis and predicting the various modes of laminate failure through the use of the average stress criterion as o riginally suggested and through same modifications to the criterion. Several joint configurations of a composite bolt bearing specimen have been analyzed using the method discussed above. The net tension and bearing and shearout modes of failures have been predicted analytically. The analytical predictions have been compared with available experimental data and good correlation has been obtained.