Failure Mechanism Of Joints Research Articles

Mechanical Properties and Design Method of Aluminum Alloy Bolt-sphere Joints

Aluminum alloy materials have been extensively used in long-span roof structures, especially in coastal and industrial buildings containing corrosive matters. In this study, new-type aluminum alloy bolt-sphere joints were taken as research objects and evaluated through tensile test and numerical simulation. The tensile properties and failure mechanism of the aluminum alloy bolt-sphere joints were explored. A calculation formula for the tension capacity of aluminum alloy bolt-sphere joints was proposed. The following conclusions were drawn based on the test data and the numerical simulation results: (1) the tension capacity of aluminum alloy bolt-sphere joints is controlled by the tensile properties of seal plates and the uplift-resistant properties of stainless steel bolts; (2) as the thickness of the seal plate increases, its main tensile failure modes are the combined tensile and shear failures at the ring crush part of the aluminum pipe, the tensile failure at the ring crush part of the aluminum pipe, and the tensile failure of the stainless steel bolt; (3) the tensile failure modes of the bolts are mainly the rupture failure of the bolt member and the shear failure of the thread according to the different screwing depths of the bolts into the sphere; and (4) the screwing depth of the bolt into the sphere should be more than 1.6d (d is the diameter of the stainless steel bolt); (5) the proposed calculation formula is accurate and effective.

Self-piercing riveted-bonded hybrid joining of carbon fibre reinforced polymers and aluminium alloy sheets

Abstract The mechanical properties and failure mechanisms of self-piercing riveted-bonded hybrid joints with carbon fibre reinforced polymers (CFRP)/aluminium alloy 5754 are investigated. The effects of the sheet thickness and the ply angle of CFRP on the joints performance are analysed. Tensile shear tests were performed to determine the mechanical behaviour and failure modes of different joints. The failure fractures in the rivet holes were analysed by a scanning electron microscope to characterize the various damage mechanisms of the CFRP. The results show that the joints with 0°/90° ply had the optimum mechanical properties and failed by adhesive and locked structure failure, while fibre fractures, matrix cracks and delamination of CFRP were common in the joints with ±45° ply or complex angle ply. Numerous fibre fractures and fibre peeling occurred in the rivet holes of the joints with complex angle ply, causing serious damage in the bearing region; these joints had the poorest energy absorption capacity. Increasing the CFRP thickness significantly enhanced the strength of the ±45° ply joints and significantly increased the energy absorption of the joints with complex angle ply.

Ductile Fracture Analysis of Welded Hollow Spherical Joints Subjecting Axial Forces with Micromechanical Fracture Models

Two micromechanical fracture models, void growth model (VGM) and stress modified critical strain (SMCS) model, were adopted to distinguish the failure mechanism of welded hollow spherical (WHS) joints under axial load based on FE analysis. Ductile fracture was successfully predicted for WHS joints under axial tension. The predicted fracture location is at the weld toe between WHS joints and circular hollow section members, which is consistent with corresponding test results. The predicted fracture load is lower than the peak load on the load–displacement curve, which indicates that the failure mechanism of WHS joints under axial tension is fracture due to inadequate strength and the fracture load should be taken as the ultimate load bearing capacity of the joints. A simplified SMCS model was proposed and verified for ductile fracture prediction of WHS joints under axial tension. Micromechanical fracture analysis was also conducted on WHS joints under axial compression. It was obtained by both VGM and SMCS model that no fracture would occur before the load reached its peak value, the reason of which was discussed by tracing the variation of the equivalent plastic stain and stress triaxiality at the potential location of fracture. Therefore, the failure mechanism of WHS joints under axial compression is losing stability with the depression of the sphere cap and the peak load on the load–displacement curve should be taken as the ultimate load bearing capacity of WHS joints.

Experimental investigation of screwed joints capabilities for the CFRP composite laminates

The load-carrying capability of the screwed joints for the carbon fiber reinforced polymer (CFRP) composite laminates was investigated by compression and torsion tests. To this end, the M6, M8, M10, and M12 metric internal threads were obtained by tapping directly into the CFRP composite laminates. In order to avoid material damage, the milling and tapping operations were implemented using CNC controlled machine tools. Quasi-static compression and torsion tests were carried out on the simply tapped and Helicoil reinforced screwed joints in the universal tensile-press test machine under uniform test conditions. The applied force and torque values respect to the screw displacements were obtained. Based on the experimental outcomes, the load-carrying capability and failure mechanisms of screwed joints were evaluated. The SEM graphics were utilized to explain the failure mechanism of threads. The load-carrying capability of joints increased with increasing the joint size. Helicoil reinforced specimens showed significantly higher maximum failure load and torque values compared to simply tapped specimens. Although, Helicoil inserts were effective in improving load-carrying of screwed joint, analysis of Helicoil performance proved that the effectiveness of Helicoil decreased with an increase in metric screw size. The computed stripping strength values indicated that Helicoil reinforced screwed joint can be an alternative to riveted and adhesively bonded joints as a detachable joining technique for thick CFRP composite laminates.

Load-carrying capacity of welded K-type joints inside floor truss systems

The load-carrying capacity of a K-type joint inside a floor truss is studied both experimentally and numerically. The joint tested is a scaled-down, isolated joint. The tubular braces, plate chord, and division plate are made of SSAB Domex steel. Comparison of load displacement curves received by finite element analyses with curves obtained from tests confirms that numerical models describe joint behaviour reasonable. The paper demonstrates that joints with high load-bearing capacity can be investigated experimentally by scaling the dimensions of the joint down when testing devices can affect the required capacity of the joint. The results presented can also be used for optimizing failure mechanism of similar joints in practice.

Research on the Microstructure Characteristic and Tensile Property of Laser-MIG Hybrid Welded Joint for 5A06 Aluminum Alloy

Laser-metal inter gas (MIG) hybrid welding technique provides higher overall productivity over the traditional fusion welding processes for joining medium-thick aluminum alloy. In this paper, laser-MIG hybrid welding experiment was performed by the TruDisk 12003 Laser and KUKA robot. The second fusion line, the laser-dominated region and laser-MIG hybrid-dominated region were introduced to this study to discuss the microstructure distribution. A three-dimensional finite element model was established by MSC. Marc to study the thermal field distribution of laser-MIG hybrid welding process. It found that the temperature in the laser-MIG hybrid-dominated region was much higher than the laser-dominated region. The formation of the second fusion line in the welded joint is mainly owing to the different heat effect of laser-arc hybrid-dominated region and laser-dominated region. The crystalline size of equiaxed dendrite grains in the laser-MIG hybrid-dominated region is finer than the laser-dominated region. In addition, the tensile property was measured to dissect the failure mechanism of the laser-MIG hybrid welding joints. The element content in fractured surface at the position of dimple and pore wall were comprehensively analyzed. The element content of Mg and O in pore wall are higher than dimple. In the solidification process, the growth of equiaxed dendrite grains is in part hindered by the existence of coarse pores in the laser-MIG hybrid-dominated region.

Failure modes of CFRP pre-tightened single tooth joints under axial cyclic tensile loading

The fatigue behavior of a pre-tightened single tooth (PTST) joint composed of pultruded carbon fiber-reinforced polymer (CFRP) composite lamina and subjected to axial tensile loading was investigated experimentally by conducting fatigue tests and numerically by implementing finite element analysis. The pultruded CFRP composite laminae, however, are prone to interlaminar failure, thus necessitating understanding of the failure mechanism of such joints under a constant amplitude cyclic tensile load. In this work, the fatigue life of joints was obtained, and the failure mechanism was determined. Crack initiation and propagation were described, although the failure was always sudden and brittle. The dominant failure mode for all types of joints was a tooth-shear-off failure that occurred along the tooth root of the CFRP laminae. Independent of the failure mode, similar crack development was observed, characterized by initial and final regions of accelerated instability propagation and a middle interval of linear and slower crack propagation. The ratios of these three stages had significant correlations with the pre-tightening stress level especially at high pre-tightening stress, the middle stage became significantly longer, and the final stage became shorter. Considerable differences were observed for fatigue failure modes under different tooth lengths and pre-tightening stress levels.

The out-of-plane behaviour of concrete masonry infills bounded by reinforced concrete frames

The paper presents results of a finite element (FE) study of several critical geometric parameters on the out-of-plane behaviour of concrete masonry infills bounded by reinforced concrete (RC) frames. The development of FE model adopted a three-dimensional simplified micro-modeling technique considering detailed geometry and behaviour characteristics of concrete and masonry units through Concrete Damaged Plasticity (CDP) method. The surface-based cohesive interaction was incorporated to capture the behaviour and failure mechanisms of mortar joints. A concurrent experimental study was also conducted on four infilled RC frames and the results were used to validate the FE model. The model was shown to be capable of simulating accurately the out-of-plane behaviour and strength as well as capturing the cracking pattern and failure modes of infilled RC frames for different geometric and loading situations. The parameters considered in the FE study included infill aspect ratio, infill slenderness ratio, bounding frame stiffness, frame-to-infill interfacial gap, infill opening size and aspect ratio, and web thickness of masonry blocks. The numerical results showed that the out-of-plane behaviour of infilled RC frames was dependent on these parameters and the correlation between each parameter and its effect on the infill strength was described as appropriate.

Mechanical Investigation on Interface Failure Mechanisms of Dissimilar Welded Joints

Mechanical Investigation on Interface Failure Mechanisms of Dissimilar Welded Joints

Finite Element Analysis of Anchor Leg Improved Trough Embedded Parts Based on ABAQUS

Reasonable and accurate simulations of failure behaviors of steel-concrete composite members with trough embedded parts is of great significance for the study of joint failure mechanism of prefabricated components in assembled buildings. Based on the implicit solution module of ABAQUS, the anchor legs of 5234 trough embedded parts are redesigned. The cylindrical anchor legs are designed as anchor plates with different diameter holes. The finite element model of the anchor leg of improved 5234 trough embedded parts and that of concrete are established. The mechanical properties of the specimens under bending and shear failure are simulated. And take a research on the improved trough embedded parts. The results show that the ultimate stress of concrete and the ultimate stress of embedded parts decrease first, then increase and then decrease with the increase of the diameter of circular hole, and the displacement of anchor leg of embedded parts decreases first and then increases with the increase of the diameter of circular hole. When the diameter of circular hole is 10.0 mm, the ultimate stress of concrete, the ultimate stress of embedded parts and the displacement of anchor leg are the smallest, and the mechanical properties of embedded parts are improved the most.

Experimental and numerical analysis of fracture parameters of adhesively bonded joints at low temperatures

In this work, the fracture parameters of the adhesive joints were investigated at low temperatures. The results of the tensile experiments showed that by decreasing the temperature, the ultimate strength, yield strength and elastic modulus have increasing trends. The effect of temperature and loading mode on the fracture toughness parameters of adhesive joints were examined by using the special test loading device in which by varying the loading angle, pure mode I, II and mixed mode data were obtained experimentally. The results showed that by decreasing the temperature, critical stress intensity factors and critical strain energy release rates increased. However, the increasing trend in mode I was gentle and in mode II was significant. Non-dimensional stress intensity factors were also determined by using finite element method at low temperatures and different loading modes. In order to understand the failure mechanism of adhesive joints, fracture surfaces of samples were analyzed, which showed that, in mode I, the failure mechanism was of a cohesive type and by decreasing the temperature, the joint became brittle and the fracture surface became smooth. The interfacial failure in mode II revealed that the fracture toughness of the adhesive was greater than that of the interface, which leads to deviation of crack growth path from the cohesive to the interfacial fracture.

Low speed impact behaviour of adhesively bonded foam-core sandwich T-joints

This paper investigates the effects of foam core density and aluminum skin plates on the low speed impact behaviour of adhesively bonded sandwich T-joints having a PVC foam core and aluminum face-sheets. The dynamic response of adhesively bonded sandwich T-joints was analyzed by the explicit finite element method. Two different material models were implemented to the foam core material: a hyperelastic model and a crushable foam material with ductile damage whereas the aluminum face-sheets were modelled as an elasto-plastic material. The cohesive response of adhesive interfaces was included using three dimensional cohesive element based on cohesive zone model. Adhesively bonded sandwich T-joint specimens were manufactured and tested to validate the numerical model. A very good agreement between the experimental and FE results were achieved. The density of the foam core material of adhesively bonded sandwich T-joint played important role on the joint failure mechanism. The joint having a stiffer foam core experienced more damage in both stiffener panel and adhesive layers.

Comparison of shear strength and failure mechanisms of lap joint between REBCO tapes bonded by different joining techniques

Lap joints between Rare-Earth Barium Copper Oxide (REBCO) tapes are intended to be employed for segmented fabrication of high-temperature superconducting magnet as innovative design of fusion magnets. This study evaluates the shear strength and failure mechanism of lap joints between commercial REBCO tapes from two different manufacturers while using different mechanical joining procedures or soldering alloys. Additionally, the shear strength along the width direction of the different REBCO tapes was experimentally evaluated. Overall results using REBCO tapes with soldered Cu stabilizer revealed that they are unsuitable for field application due to low shear strength of the tapes. On the other hand, REBCO tapes with electro-plated Cu stabilizer are more versatile; soldered lap joints using Pb37Sn63 showed shear strength higher than required value. However, failure mechanism of the soldered joints always involve delamination of the REBCO tape which instantly increase joint resistance. Conversely, mechanical lap joints with indium fabricated using the improved method with heat treatment or indium pre-coating with heat treatment exhibited cohesive failure followed by plastic deformation of indium, which reduces the shear stress while maintaining acceptable joint resistance. This fact makes the mechanical lap joint a more reliable option so far.

Effect of bolt threads on the double lap joint strength of pultruded fibre reinforced polymer composite materials

The ability to provide effective and adaptable joints for pultruded fibre reinforced polymer (PFRP) is crucial for its widespread application in civil infrastructure. This experimental based study on 150 double lap joints specimens investigated the effects of threaded bolt and clamping pressure on the joint strength behaviour, failure mechanisms and joint efficiency of bolted joints in PFRP. Double lap joints in both longitudinal and transverse directions of the laminates and with different edge distance-to-bolt diameter (e/db) were prepared and tested in accordance with ASTM D5961 standards. The joint strength in the longitudinal laminates with plain bolt increased for e/db ratio for up to 4 and with no appreciable strength gain after exceeding this ratio. On the other hand, about 30%–40% reduction in joint strength was observed in the longitudinal direction due to the bolt thread tearing through the laminates. This leads to a recommendation of 0.6 reduction factor in preliminary design of PFRP bolted connections with bolt thread present. Meanwhile, only a marginal difference of 7% was observed in transverse direction. Furthermore, the introduction of lateral clamping pressure had increased the joint strength by 60%–90% and this has lessened the thread casualty effect on the pultruded composite joints.

Experimental and numerical study on the longitudinal-crack failure of double-shoulder tool joint

In recent years, the failure accidents of double-shoulder tool joint caused by longitudinal-crack occur frequently during drilling with increasing deep and ultra-deep wells, directional wells, extended reach wells and horizontal wells, which not only decreases rate of penetration, but also results in huge economic losses. Although the frictional heat check cracking can cause cracking initiation according to the standard API RP 7G, it has been found heat check cracking is just one of the cracking initiation mechanism rather than crack propagation mechanism; in other words, there are various other causes of crack initiation and propagation. Hence, in order to find out the failure mechanism caused by longitudinal-crack, the failure analysis of one typical double-shoulder joint with longitudinal crack has been investigated in detail from three aspects including its service load, its own structure feature and fracture toughness by combining experimental inspection and finite element simulation. The results from macro-analysis, micro-analysis, chemical component analysis, mechanical properties analysis, stress and deformation analysis, show that this failure mechanism of double-shoulder joint is closely and directly related to overlarge combined load (tensile force, torsion and bending), its own structure feature and difference of fracture toughness between transverse section and longitudinal section. Firstly, the martensite is produced on the thread surface due to severe fraction heat between threads caused by overlarge combined load during jarring releasing of double-shoulder joint, which leads to the inter-granular crack initiation. Secondly, the circumferential stress release is restricted by thread connection. Thirdly, the transverse fracture toughness of material is lower than longitudinal fracture toughness. Finally, the longitudinal-crack failure of this double-shoulder joint occurs under overlarge alternating combined load. It is suggested that if the thread taper of double-shoulder joint is decreased and the area of secondary shoulder is increased under extreme working environment, the bearing capacity of connection can be improved and the failure accident caused by longitudinal-crack can be avoided effectively.

Vibration effects on tensile properties of adhesively bonded single lap joints in composite materials

The aim of this study is to investigate the effects of cyclic‐vibration‐loading on failure loads of adhesively bonded composites. For this purpose, experimental studies were performed for composite adherents with single lap joint. Manufactured eight‐layered E/glass‐epoxy composite plates with single lap joints were subjected to dynamic cyclic loading via vibration motor, which delivered a force of 160 N at a frequency of 50 Hz. and then tested under tensile loading to investigate the joint strength. The behavior of adhesively bonded joints under various vibration cycles was observed and failure mechanisms of joints were also discussed. It was observed that a significant decrement in the strength of the vibrated joints when compared with that of the non‐vibrated joints. However, the joint performance increased up to a certain value of vibration load cycle. After a certain value of vibration load cycle, the joint performance dropped suddenly. Besides, the light‐fiber‐tear failure was observed in the overlap region of all joints. POLYM. COMPOS., 40:1258–1267, 2019. © 2018 Society of Plastics Engineers

Elasto-plastic finite element analysis of reinforced concrete T-shaped column frame joint

By the integral finite element analysis of elasto-plastic constitutive relationship, the process of crack formation and development of the T-shaped frame joint in reinforced concrete and its stress distribution under monotonic and low-cycle repeated loading were studied . The nonlinear constitutive relation of concrete and the failure mechanism of T-shaped column joint were further discussed. The work of this paper provides a reference to the design and construction of T-shaped column joints.

Degradation of joint surface morphology, shear behavior and closure characteristics during cyclic loading

In order to investigate the failure mechanism of rock joint, a series of laboratory tests including cyclic direct shear tests under constant normal load(CNL) conditions were conducted. Morphology parameters of the rock joint surface were precisely calculated by means of a three-dimensional laser scanning machine. All test results were analyzed to investigate the shear behavior and normal displacement behavior of rock joints under CNL conditions. Degradation of rock joint surface during cyclic shear tests was also analyzed. The comparison results of the height parameters and the hybrid parameters of the joint surface during cyclic tests show that the degradation of the surface mostly happens in the first shear and the constant normal loads imposed on the joints have significant promotion effects on the morphology degradation. During cyclic shear tests, joints surfaces evolve from rough state to smooth state but keep an overall undulation. Dilatancy of rock joints degrades with the degradation of joint surface and the increase of normal loads. The closure deformation of joint is larger than that of the intact rock, and the normal stiffness increases with the increase of shearing times.

Failure load prediction of composite bolted joint with clamping force

Clamping force significantly affects the failure mechanisms of bolted joints. In order to predict the failure load of bolted joints, the effect of clamping force must be considered. In this paper, failure load prediction for composite joints with clamping force was conducted using a characteristic length method combined with Tsai-Wu failure criteria. Tensile and bearing tests and stress analyses were conducted to determine tensile and compressive characteristic lengths. A characteristic curve was used to perform failure load prediction for single lap-shear bolted joints. This prediction was accompanied by experiments and stress analysis. The predicted failure load was compared with the actual failure obtained from experiments, and the results were found to be in good agreement.

Strength and Failure Mechanism of Composite‐Steel Adhesive Bond Single Lap Joints

Carbon fiber‐reinforced plastics‐ (CFRP‐) steel single lap joints with regard to tensile loading with two levels of adhesives and four levels of overlap lengths were experimentally analyzed and numerically simulated. Both joint strength and failure mechanism were found to be highly dependent on adhesive type and overlap length. Joints with 7779 structural adhesive were more ductile and produced about 2‐3 kN higher failure load than MA830 structural adhesive. Failure load with the two adhesives increased about 147 N and 176 N, respectively, with increasing 1 mm of the overlap length. Cohesion failure was observed in both types of adhesive joints. As the overlap length increased, interface failure appeared solely on the edge of the overlap in 7779 adhesive joints. Finite element analysis (FEA) results revealed that peel and shear stress distributions were nonuniform, which were less severe as overlap length increased. Severe stress concentration was observed on the overlap edge, and shear failure of the adhesive was the main reason for the adhesive failure.