Failure Mechanism Of Joints Research Articles

Research on the Seismic Behavior of Concrete-Filled Steel Tubular Column and Steel Beam Joint

Joints are the forces cross points of members, and the bearing modes are more complex than other members, especially under earthquake action, so the rationality of joints are directly related to the safe reliability of structure. By the pseudo-static test of 4 concrete-filled square steel tubular column and steel beam joint with outer stiffened ring, this paper discusses the failure characteristics, failure mechanism and seismic behavior of joints under different axial compression ratio. The analysis of the testing results shows: the energy dissipation capacity of joints is much better, the degradation of strength and stiffness are slowly when reached the ultimate strength, and the ductility is also good.

Effets de la rTMS haute et basse fréquence sur le cortex temporal : résultats préliminaires

Adhesive joints have a wide range of applications in the civil engineering, automotive and aircraft industries. In the present research, we use the finite element method to systematically study the overall strength and interface failure mechanism of single lap joints, which are subjected to tensile loading, focusing on the effects of various system parameters including fracture energy of the adhesive layer, overlap length and adhesive layer thickness on the load-bearing capability of the joints. The results show that the overlap length and the adhesive fracture energy have combined influences on the load-bearing capability. On the other hand, a preliminary damage analysis of the adhesive layer is carried out, considering the situations when the loads arrive to the peak values. Furthermore, the interface behavior is investigated, including the interface stress analysis and interface slip. The rotation of the joint during loading and its influence factors are studied as well. Obtained results suggest that the interface stress distributions are related to the slip and the rotation angle.

Cyclic Tests on External RC Beam-Column Joints: Role of Seismic Design Level and Axial Load Value on the Ultimate Capacity

A wide experimental program on beam-column RC joints carried out in the framework of the DPC-Reluis Project (DPC: Department of Civil Protection, Reluis: Network of University Laboratories of Earthquake Engineering) is presented. All the experimental tests were performed at the Laboratory of Structures of the University of Basilicata, Potenza, Italy. The main objective of the experimental campaign is to study and compare the post-elastic behavior of beam-column joints with different earthquake-resistant design levels, indicating the role of some structural parameters such as the axial load value acting on the column, beam dimensions, and steel type, on the joint performances and failure mechanism. The analyses have mainly been devoted to improving the assessment procedures regarding existing buildings but also to verifying the prediction capability of the capacity models relevant to beam-column joints contained in literature and in the new seismic codes. Following a short description of the experimental methodologies used in other campaigns, the experimental program is presented, providing a detailed description of the specimens and of the testing set-up. This is followed by a report of the main results of the cyclic tests performed on the beam-column specimens that highlight the role played by axial load and seismic design level in determining the failure mechanism and the global response of the joints.

Structural Behavior of CHS T-Joints Subjected to Brace Axial Compression in Fire Conditions

The structural behavior of circular hollow section (CHS) T-joints subjected to axial brace compression in fire conditions was investigated. Five full-scale tubular joints with different brace-to-chord diameter ratios were tested under elevated temperature. The tests were in isothermal heating conditions, where the specimens were heated to the desired temperatures and then subjected to static load to failure. The ultimate strength and failure modes of these joints were investigated. It was observed that both the reduction in material strength and changes in localized plastification area beneath the brace decreased the ultimate strength of the joints as temperature increased. Furthermore, local buckling and ovalisation of the chords were found to be more concentrated around the joint region at elevated temperature. To the authors’ best knowledge, these tests were among the first reported experimental investigations in the ultimate strength and failure mechanisms of tubular joints at elevated temperature. To investigate the joint behavior at high temperature in greater detail, FEM was used. The finite-element models were first validated by the test results. The development of failure mechanisms of CHS T-joints at elevated temperature was then traced with the numerical models. The models were also used to quantify the effect of elevated temperatures on three parameters that directly affect the ultimate strength of the T-joints. The three parameters are boundary condition, precompression in the chord, and chord thickness.

Load-carrying capacity and practical calculation method for hollow cylinder joints connected with H-shaped beams

A type of hollow cylinder joints connected with H-shaped beams is proposed for spatial structures. Based on von Mises yield criterion and perfect elasto-plasticity model, a series of finite element models of the joints is established, in which the effect of geometric nonlinearity is taken into account. Then mechanical behavior and load-carrying capacity of the joints were investigated, which were subjected to axial load, in- and out-plane bending moments, and their combinations. The results show that the ultimate loads of the joints are determined by the maximum displacement. Furthermore, the case of one joint connected with multiple beams was discussed. Experiments on a set of typical full-scale joints were conducted to understand the structural behavior and the failure mechanism of joint, and also to validate the finite element models. Finally, the practical calculation method was established through finite elements analysis (FEA) results and numerical fitting. The results show that the joints are more ductile and materially economical than welded hollow spherical joints, and the practical calculation method can provide a reference for direct design and the revision of relevant design codes.

The Diagnostic Protocol for Evaluation of Periprosthetic Joint Infection

Infection is becoming the most important as well as the most devastating mechanism of prosthetic joint failure. The incidence is increasing because the absolute number of patients operated is increasing and because more often very sick, debilitated and immunocompromised patients are operated. The trend reveals a further increase in the years to come. Diagnosis may be very easy in case of high grade processes, but also extremely difficult in some other instances. Misdiagnosing infection leads to repeated early failures that are distressing for patients as well as surgeons. To avoid failures related to misdiagnosed prosthetic joint infections a step-wise algorithm of action is proposed and the diagnostic strength of the steps discussed. The key point is to select potential candidates to define the probability of an ongoing infection and then to select the tools to strengthen the suspicion. Further procedures are based on the analysis of the pseudo-synovial fluid obtained by aspiration. Diagnostic conclusions form the basis for treatment decisions.

Strength and interface failure mechanism of adhesive joints

Adhesive joints have a wide range of applications in the civil engineering, automotive and aircraft industries. In the present research, we use the finite element method to systematically study the overall strength and interface failure mechanism of single lap joints, which are subjected to tensile loading, focusing on the effects of various system parameters including fracture energy of the adhesive layer, overlap length and adhesive layer thickness on the load-bearing capability of the joints. The results show that the overlap length and the adhesive fracture energy have combined influences on the load-bearing capability. On the other hand, a preliminary damage analysis of the adhesive layer is carried out, considering the situations when the loads arrive to the peak values. Furthermore, the interface behavior is investigated, including the interface stress analysis and interface slip. The rotation of the joint during loading and its influence factors are studied as well. Obtained results suggest that the interface stress distributions are related to the slip and the rotation angle.

Defects classification and failure modes of electrofusion joint for connecting polyethylene pipes

AbstractAs electrofusion (EF) technology is widely used in connecting polyethylene (PE) pipes and other plastic pipes or composite pipes, research in safety assessment of EF joints has been of major concern. EF joints with defects are very common in practical applications. These defects may greatly reduce the mechanical performance of the EF joints and threat safety running of the pipeline system. To evaluate hazard of these defects and provide a basic understanding for the failure mechanism of EF joints, a comprehensive study on defects and failure modes is conducted in this work. The defects in EF joints are classified into four categories: poor fusion interface, over welding, voids, and structural deformity. The forming reasons of these defects are analyzed in detail. The mechanical properties of EF joint containing these defects are investigated by conducting peeling tests and sustained hydraulic pressure tests. Test results show that there are three main failure mode of EF joint under inner pressure, that is, cracking through the fusion interface, cracking through the fitting, and cracking through copper wire interface. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Pullout Test Study on Flexible Joint of Ductile Iron Buried Pipelines

Axial pullout test on ductile iron buried pipelines with MTS testing machine was carried out, the relation curve between axial tension and flexiable joint displacement was gotten, the functional failure mechanism of flexible joint of buried pipeline was discussed. The results indicate that there is relative displacement between pipe and soil under seismic action, meanwhile, the acting force between pipe and soil is the viscous damping force which is related to pipe-soil relative speed.

Finite Element Analysis of the Cyclic Stress Amplitude of Threaded Fasteners Using Helical Thread Models

Fatigue failures of bolted joints frequently lead to serious accidents in machines and structures. It is well known that fatigue failure is likely to occur around the first thread root of the bolt adjacent to the nut loaded surface and the run-out of bolt thread. That is because high stress amplitudes are generated there due to alternating external forces. Accordingly, it is significantly important to evaluate the stress amplitudes along the thread root in order to rigorously examine the fatigue failure mechanism of bolted joints. In this study, stress amplitude distributions along the thread helix including the thread run-out are analyzed by three-dimensional finite element analysis. The numerical models of the bolted joints are constructed so as to accurately represent the effect of thread helical geometry, using the modeling scheme proposed in the previous study which analyzed the stress concentrations at the thread root. The analytical objectives are bolted joints with axisymmetric geometry except for the helical-shaped threaded portions that are subjected to axisymmetric external forces. It has been substantiated, based on the stress amplitude distributions along the thread helix, which the fatigue failures are likely to originate from the first bolt thread, as in the case of the maximum stress, and the run-out of threads. It has also been shown that a bolt with reduced diameter is effective for the purpose of lowering the stress amplitude at the first thread root of bolt.

Recent development in finite element analysis of self-piercing riveted joints

Self-piercing riveting (SPR) is a high-speed mechanical fastening technique which is suitable for point-joining advanced lightweight sheet materials that are dissimilar, coated, and hard to weld. Major advances have been made in recent years in SPR technique. Latest literature relating to finite element analysis (FEA) of SPR joints is reviewed in this paper. The recent development in FEA of SPR joints are described with particular reference to three major factors that influence the success of SPR technique: SPR process, failure mechanism, and mechanical behavior of SPR joints. The main FE methods used in FEA of SPR joints are discussed and illustrated with brief case studies from the literature. Areas where further useful progress can be made are also identified.

Numerical Analysis on Failure Mechanism of Intermittent Joints

The mechanical characteristics of jointed rocks are mainly controlled by geometrical features of intermittent joints. The failure mechanism and shear behavior of discontinuous joints are simulated by series of direct shear tests using the particle flow code (PFC2D). The effects of joint persistence, separation and azimuth angle on the failure strength of jointed rock are studied in detail. The results shows that peak shear strength can be considered as a function of the geometrical parameters, which is in a reasonable accordance with other experimental results. Meanwhile, as for failure mechanism, joint separation and azimuth angle are especially discussed, and specific damage patterns are presented as well.

Shear Mechanism and Bearing Capacity Calculation of Composite Joints with Steel Truss SRC Beam

In order to research the seismic performance, eight joints with steel truss SRC beam and RC column under low-cyclic reversed load was conducted, and the failure process and patterns were observed. The test indicates that two types of failure patterns can be seen from specimens, including shear failure and bending failure. By the analysis of the failure characteristics and mechanism of joints, the load-displacement hysteretic curves and load-strain hysteretic curves are presented, and the formula for calculating ultimate shear capacity of joints is gained finally. The calculating results are in good agreement with those of tests.

PULL-OUT STRENGTH OF MORITISE-TENON JOINT WITH PIN SUBJECTED TO BENDING MOMENT

To investigate the failure mechanism and structural performance of mortise-tenon joints subjected to tensile force under a constant bending moment, pull-out tests of mortise-tenon joint specimens under bending moments were carried out. It is found from the tests that the pull-out strength of a joint, subjected to a damage limit bending moment, increased by comparison with a case of free bending moment. In the case of a safety limit bending moment, the tensile strength was reduced due to bending failure of the tenon. The failure mechanism was also discussed using FEM and macro models.

Damage sensing of adhesively-bonded hybrid composite/steel joints using carbon nanotubes

Carbon nanotube networks have been used previously for in situ sensing of matrix damage in fiber-reinforced composites. In this research, the ability of carbon nanotube networks to sense and distinguish different types of damage in adhesively-bonded hybrid composite-to-metal joints is evaluated. Toward this end, conductive networks of carbon nanotubes are introduced to the composite substrate as well as the epoxy adhesive. By altering the geometry and chemically treating the steel substrate surface, different failure mechanisms of the single-lap shear joints are achieved. It is demonstrated that these failure mechanisms each possess a distinct resistance response, therefore proving the ability to not only sense failure in situ, but also to distinguish the extent and nature of damage which occurs.

Analytical evaluation of the failure mechanism of loop-shaped re-bar joint using RBSM

Analytical evaluation of the failure mechanism of loop-shaped re-bar joint using RBSM

Grooved Ball Pad Structure (GBPS) to Improve FBGA Solder Joint Reliability (SJR) Performance

In this paper, a novel concept using the circular grooved ball pad structure (GBPS) for FBGA is proposed. The goal of the new design is to significantly improve FBGA solder joint reliability (SJR), with minimal impact in cost and packaging assembly processes. Finite element analysis (FEA) tools are used to understand the package solder joint failure mechanism. Simulation shows the GBPS can improve FBGA package SJR significantly. The leadframe based ball grid array package (LFBGA) is chosen as the vehicle to demonstrate the concept of grooved ball pad structure. The reliability results show that GBPS can improve LFBGA package SJR cycles by 2X. Grooved ball pad technology is further attempted on wafer level chip scale packages (WLCSP).

On the Design of RC Beam-column Joints to Hong Kong Concrete Code 2004

In the current Hong Kong ‘Code of Practice for Structural Use of Concrete 2004’, one of the major differences from its previous versions is the inclusion of design of reinforced concrete beamcolumn joints, which was not addressed before. The design criteria for beam-column joints in the Code are based largely on those in New Zealand design code NZS 3101. Nevertheless, most of the structural engineers in Hong Kong are not familiar with the related background materials and design philosophy, as well as the design procedure. In view of the situation, this paper aims to discuss the behaviour and failure mechanisms of RC beam-column joints and to comment on some of the design criteria in the Code. Design examples are given to show the procedure and calculations for design and detailing of different types of RC beam column joints to the current code of practice.

ねじ山らせんモデルによるボルト締結体の疲労強度評価

Fatigue failures of bolted joints frequently lead to serious accidents of machines and structures. It is well known that fatigue failure is likely to occur around the first thread root of bolt adjacent to the nut loaded surface and the run-out of bolt thread. That is because high stress amplitudes are generated there due to alternating external forces. Accordingly, it is significantly important to evaluate the stress amplitudes along the thread root in order to better define the fatigue failure mechanism of bolted joints. In this study, stress amplitude distributions along the thread helix including the thread run-out are analyzed by three-dimensional finite element analysis, where the numerical models of bolted joints are constructed so as to accurately take account of the effect of thread helical geometry, using the modeling scheme proposed in the previous paper. The analytical objectives are bolted joints with axi-symmetric geometry except for the helical-shaped threaded portions, and are subjected to axi-symmetric external forces. It has been substantiated, based on the stress amplitude distributions along the thread helix, that the fatigue failures are likely to originate from the first bolt thread, as in the case of the maximum stress, and the run-out of threads. Also shown is that the fatigue failure location varies depending on the distance between the target bolt and the loading position and whether or not there is a separation at the plate interface.Copyright © 2009 by ASME

Experimental and numerical analysis of BGA lead-free solder joint reliability under board-level drop impact

Board-level solder joint reliability is very critical for handheld electronic products during drop impact. In this study, board-level drop test and finite element method (FEM) are adopted to investigate failure modes and failure mechanisms of lead-free solder joint under drop impact. In order to make all ball grid array (BGA) packages on the same test board subject to the uniform stress and strain level during drop impact, a test board in round shape is designed to conduct drop tests. During these drop tests, the round printed circuit board assembly (PCBA) is suffered from a specified half-sine acceleration pulse. The dynamic responses of the PCBA under drop impact loading are measured by strain gauges and accelerometers. Locations of the failed solder joints and failure modes are examined by the dye penetration test and cross section test. While in simulation, FEM in ABAQUS software is used to study transient dynamic responses. The peeling stress which is considered as the dominant factor affecting the solder joint reliability is used to identify location of the failed solder joints. Simulation results show very good correlation with experiment measurement in terms of acceleration response and strain histories in actual drop test. Solder joint failure mechanisms are analyzed based on observation of cross section of packages and dye and pry as well. Crack occurred at intermetallic composite (IMC) interface on the package side with some brittle features. The position of maximum peeling stress in finite element analysis (FEA) coincides with the crack position in the cross section of a failed package, which validated our FEA. The analysis approach combining experiment with simulation is helpful to understand and improve solder joint reliability.