Behavior Of Composite Joints Research Articles

Dynamic behavior of composite joints in hydrodynamic ram simulator

The fracture behavior of carbon/epoxy composite joint structures under highly dynamic pressure loading was studied experimentally and numerically. The considered dynamic pressure loading, called hydrodynamic ram (HRAM), potentially causes fractures in structures filled with fluid. First, experiments using the HRAM simulator method were carried out to monitor the fracture behavior of the composite joint structure. In the experiment, highly dynamic pressure loading was generated which propagated and initiated the fracture of the composite joint. Next, numerical simulation was performed through finite element analysis using LS-DYNA. The dynamic pressure loading inside the fluid was predicted using the arbitrary Eulerian Lagrangian (ALE) method and the fracture behavior of the composite joint structure was simulated using cohesive zone modeling (CZM). The analysis was validated by comparing the predicted results with those from the experiment. The predicted pressure loadings were well-matched with the experimentally measured ones. The strain histories and failure strain values obtained by the analysis also agreed reasonably well compared to those in the experiment for selected points in the composite structure. Finally, the effects of impact velocity and the stiffness of the joint structure on the fracture behavior were examined.

Rotation capacity of composite joints for slim‐floor beams

AbstractThe analysis of a composite beam‐to‐column structure requires knowledge about, on the one hand, the behaviour of beams and columns and, on the other, the joints between such elements. For beam‐to‐column joints, for example, the lack of appropriate design rules forces structural engineers to model joints as pinned, despite the fact that a certain joint rigidity and bending resistance is available because of the upper reinforced concrete slab. In this context, a research programme with experimental and numerical investigations was initiated at the University of Luxembourg [1]. This aim of this research was to identify the influence of two major joint components – the reinforced concrete slab and the steelwork connection – on the behaviour of composite joints under a hogging bending moment. Eight experimental tests were performed on beam‐to‐column joints. These tests were used to validate an FE model developed with the ABAQUS software, which allowed the simulation of further joint configurations without the need for additional laboratory tests.This article presents the results of experimental and numerical analyses. Good agreement was achieved between experimental tests and numerical simulations. The influence of the reinforcement and the steelwork connection on the structural properties of composite joints is derived and a new analytical method is proposed to determine the stiffnesses and rotation capacities of composite joints.

Surface Topography Influences on the Fatigue Behavior of Composite Joints

The surface condition of carbon fibre reinforced plastic (CFRP) substrates is decisive to obtain high bond strength and lifetime of adhesively bonded parts. Those surfaces were adjusted in terms of their microscopic topography by means of peel plies and release foils. The subsequent surface treatment via atmospheric pressure plasma jet or vacuum blasting allowed the modification of the microscopic roughness as well as the surface chemistry. Those configuration were assessed using surface analytic methods as well as quasi-static and cyclic fracture tests on single lap shear specimens. The microscopic surface roughness, if at all, only showed a small influence on the bond strength. Despite release agent residues, fracture was found within the fiber-matrix interface, which caused difficulties in evaluating the effect of surface pretreatments on the adhesion strength. Fatigue tests revealed a lifetime reduction of uneven microscopic rough surfaces, which was assigned to stress concentrations at the tip of asperities. The crack propagation was accelerated in case of release agent residues. If surfaces were free of contaminations, no differences between microscopically smooth and slightly structured surfaces were found. Overall, fatigue testing on single lap shear specimens showed an increased sensitivity with regard to the assessment of surface morphology.

Monitoring the fatigue crack growth behavior of composite joints using in situ 2D-digital image correlation

ABSTRACTTo predict lifetime and damage tolerance of adhesively bonded joints, crack growth behavior need to be understood, as it oftentimes serves as a basis or proof of, e.g., numerical models. Within this work, a method is presented to measure crack length in dynamically loaded adhesively bonded CFRP-joints by means of 2D digital image correlation. Automated picture acquisition at the maximum force level within a cycle allows measurements during the fatigue testing. The strain level in front of the crack tip was defined as maximum possible strain within the bond line. Higher strains were denoted as crack. Marking the crack path automatically led to the associated crack length and could afterward be derived to a crack propagation rate. Different destructive tests were carried out on composite single, double and crack lap shear specimens.

Behaviour of composite joints with concrete encased CFST columns under cyclic loading: Experiments

Concrete-encased concrete filled steel tube (CFST) columns have been applied in some real structures in recent years, where they were connected with reinforced concrete (RC) beams or steel beams in a building. Seven composite joint models, including four concrete-encased CFST column to RC beam joints and three concrete-encased CFST column to steel beam joints, were thus tested and compared under constant axial load on the top of the column and cyclic load at the end of the beam. The main test parameters included the joint type, axial load level on the composite column and the existence of the RC slab or not. Based on the test results, the strength, ductility, rigidity degradation, and dissipated energy of the specimens were investigated. It was found that the composite joints displayed favourable seismic performance and might be applicable in earthquake-prone regions.

Behavior of Rigid Composite Joint under Combination of Bending Moment and Tensional Force

In recent years, the progressive collapse of buildings increases the interest in progressive collapse studies. If a key column fails in structure, the internal force is redistributed by the catenary action of joint to prevent its progressive collapse. The joint connecting to the failed column is under the state of bending moment combined with tensional force and the tensional force would affect the moment-resistance ability and ductility of joint. In this paper, the finite element software ABAQUS is applied to analyze the behavior of composite joints under the state of bending moment combined with tensional force. The effects of rebar ratio, rebar strength, concrete strength, etc., on the behavior of joints are investigated. The results show that high strength steel is suggested to be used in composite joint to improve its bending moment capacity and tensional capacity.

Recent developments in composite connections

AbstractEurocode 4 [1] suggests design rules for the evaluation of the mechanical properties of steel‐concrete beam‐to‐column composite joints (rotational stiffness, resistance and ductility). These rules cover situations where the joints are subjected to moments and shear forces, but in hogging regions only (negative bending moments). Recently, researches have been conducted on the behaviour of composite joints (Fig. 1) subjected to positive bending moments (called “sagging moments” in the following) and combined bending moments and axial loads; for instance, these loading situations may appear in composite sway frames under conventional loading and exceptional actions (impact, explosion …) leading to the loss of a structural column [2].In the present paper, the Eurocode 4 design rules are extended to joints in sagging regions and to joints subjected to combined bending moments and axial loads and the proposed methods are validated through comparisons with experimental test results. An easy‐to‐use and freely available software for the design of composite joints according to the Eurocode 4 principles is also described.

Effect of Bolt Tightness on the Behavior of Composite Joints

This study provides an experimental and analytical investigation of the behavior of a double bolted single lap shear composite joint. Various scenarios of bolt tightness are considered for composite-to-composite and composite-to-aluminum bolted joints. Progressive damage analysis is provided for the composite coupons in two regions; namely, the surface under bolt heads and near the contact with the shank of the bolt; the damage analysis is performed using an optical microscope. Four tightening configurations are used in the testing of each double bolted joint. These configurations permit each of the two bolts to be either tight or loose. The analytical part of the study utilizes a 3-D finite element model that simulates the bolt tightness and the multilayered composite coupons. The experimental and finite element results are correlated.