Damage Mechanism of Braid Hole Composite Bolt Joints Under Quasi–Static Tension

Analysis of Stress Evolution and Failure Behavior in the Intra-Holes of CFRP/Ti Laminate Bolted Joints

Dynamic tensile failure of CFRP/aluminum bolted joints: Experimental and numerical investigation

The dynamic tensile failure of composite/metal bolted joints is governed by the coupled effects of stress concentration, local contact deformation, and rate-dependent damage evolution. In this study, single-bolt CFRP (Carbon Fiber Reinforced Polymer)/7075 aluminum joints are found to exhibit a pronounced strain-rate strengthening effect, with the peak stress increasing from 438.18 MPa at 1000 s −1 to 579.29 MPa at 3000 s −1 . Using split Hopkinson tension bar tests with high-speed imaging, damage was consistently observed to initiate around the composite bolt hole and became increasingly localized as the strain rate increased. More importantly, the combined high-speed observations and numerical results suggest that the local failure morphology under high-strain-rate loading is closely associated with transient secondary bending and bolt tilting, which intensify compressive damage in the region perpendicular to the loading direction and thus influence the evolution of hole-edge damage. An Abaqus/Explicit model based on the three-dimensional Hashin failure criterion was developed. The model predicted the peak stress with an error of 4.08% and successfully reproduced the main damage evolution features. These results provide new insight into the rate-dependent local failure mechanism of composite/metal bolted joints and offer a useful basis for the design and assessment of impact-resistant hybrid joint structures.

Multi-scale crushing response of sandwich composite connecting rod based on thermal expansion molding technique

The lightweighting of automotive chassis structural components faces multiple challenges, including the selection of molding processes, the design of lightweight material structures, and the joining methods between metals and composites. In this study, a steel rear suspension link of an automotive chassis is taken as the research object, and a straight-type integrally molded sandwich composite connecting rod is designed and fabricated based on the thermal expansion molding technique. Compression tests are carried out on specimens with different joint molding methods and layup configurations. Digital image correlation (DIC) technology is employed to monitor the strain field in real time, and the load-displacement curves, damage evolution mechanisms, and compressive performance of the specimens are systematically analyzed. On this basis, a local ply optimization strategy is adopted to synergistically reinforce the weak load-bearing areas, further improving the compressive performance indicators of the sandwich composite connecting rod. The results show that the sandwich composite connecting rod exhibits excellent compressive strength and structural stability, and demonstrates a negative correlation in which the crushing force efficiency decreases with increasing peak load. This study provides key technical support and a practical basis for the engineering application of lightweight high-performance structural components in the automotive industry.

Modeling Crack Behavior around Holes in Glulam Beams Using the WoodST Constitutive Model Based on Continuum Damage Mechanics

The integration of service holes in glulam beams is increasingly common in mass timber construction; however, these openings introduce stress concentrations that can compromise structural integrity through crack initiation and propagation. This study presents a robust numerical framework for simulating crack behavior around holes in glulam beams using the finite element software Abaqus. The framework incorporates the Wood ST constitutive model, developed based on continuum damage mechanics, to capture the anisotropic damage evolution of timber under tensile and shear loading. Key modeling components include detailed geometric representation, layer-refined meshing strategies, and cylindrical orthotropic material systems to simulate the structure of the laminations. To validate the proposed approach, six glulam beams with three configurations—without holes, with a single hole, and with two holes—were tested under a single point load at midspan. The developed finite element models were calibrated and validated using experimental data, demonstrating strong agreement in terms of load–displacement responses and observed failure modes. The results confirm the model’s capability to predict the structural resistance and deformation behavior of perforated glulam beams. This predictive tool contributes to the advancement of structural design methodologies for engineered timber structures.

Open-hole flexural damage response of Z-fiber reinforced hybrid woven composites

Drilled holes and through-thickness reinforcement influence the mechanical behavior and damage propagation of load-bearing composite structures. This study examines the combined effects of hole diameter, inter-layer hybridization, and stitching on the flexural response and internal damage propagation of woven composites. Carbon fiber, glass fiber, and hybrid glass/carbon composites with identical layer counts were manufactured and reinforced through the thickness using Dyneema ® stitch yarn in a cross-stitch pattern. Circular holes of 4, 6, and 8 mm were introduced. Mechanical behavior was evaluated using three-point bending tests. Internal damage before and after flexural loading was characterized using ultrasonic C-scan imaging, followed by image-based damage quantification. Increasing hole diameter reduced flexural strength and flexural modulus due to increased stress concentration and reduced effective load-bearing area. Carbon fiber–based composites showed higher strength and modulus, whereas glass fiber–based and glass-dominated hybrids exhibited greater deformation capacity. Stitching decreased flexural modulus but increased strain capacity, promoting a more ductile-like flexural response, particularly in carbon-based hybrids. Ultrasonic C-scan results further indicated that stitching restricted damage propagation in specific composite configurations. Overall, hole geometry, fiber architecture, and stitching should be considered together when designing damage-tolerant hybrid composite structures.

Finite Element Analysis of Controlled-Slip Bolted Shear Connectors for Interface Deformation Coordination in Negative-Moment Regions of Steel–UHPC Composite Beams

To improve deformation compatibility in the negative-moment regions of continuous steel–ultra-high-performance concrete (UHPC) composite girders, this study investigates a controlled-slip bolted shear connector in which bolt-hole clearance is intentionally used as a deformation-release parameter. A three-dimensional nonlinear push-out finite element model was developed in ABAQUS and validated against reported high-strength bolted connector tests. Parametric analyses were then conducted to clarify the effects of bolt-hole clearance, bolt preload, and interface friction on the load–slip response, local UHPC bearing damage, and bolt stress state. The results show that increasing the radial clearance from 0.1 mm to 2.0 mm increases the peak slip from 6.51 mm to 9.17 mm, whereas the peak resistance remains within 661.79–693.86 kN. Bolt preload mainly changes the initial frictional restraint and slip initiation, but has limited influence on the ultimate resistance. Damage and stress distributions further indicate that larger clearance delays UHPC hole-wall bearing damage, while increasing the bending–shear demand on the bolt shank. The results indicate that reserved bolt-hole clearance can be used to increase connector slip capacity while maintaining a comparable shear-resistance level within the investigated parameter range.