Failure Mechanism Of Joints Research Articles

Experimental investigation on the damage evolution and failure mechanism of segmental joints based on DOFS and AE

The damage evolution and failure mechanism of segmental joint are of great significance for the design and safety assessment for segment structures. In this study, a series of full-scale loading tests on the segmental joints adopted by the Jinan Yellow River Tunnel under positive bending loading scenario (PBLS) and negative bending loading scenario (NBLS) were conducted, introducing new measurement scheme combining distributed optic fiber sensor (DOFS) and acoustic emission (AE). The joint deformation, AE parameters, concrete strain, bolt strain and reinforcement strain are investigated. The test results show that the deformation and failure process of the joint can be divided into four stages and three stages under PBLS and NBLS, respectively. The compression-shear failure caused by the shear cracks is considered as the main failure mode of the segmental joints, and the development rate of the crack width under PBLS is obviously larger than that under NBLS. The maximum bolt strain usually occurred at the edge of the thread instead of the joint surface. The bolt under NBLS yields later than that of PBLS. Due to stress concentration, the maximum tensile strain of reinforcement under PBLS and NBLS is located near the hand hole and sleeve, respectively.

Experimental research on joining AA5052-H32/Polyoxymethylene sheets with novel stepped clinching process

The increasing availability of high-performance materials has boosted the demand for advanced joining techniques for heterogeneous sheets in the industry. The novel stepped clinching process (SCP) may become a new option for joining sheets due to the superiority in joint strength and geometric parameters compared to conventional clinching technology. The SCP for joining AA5052-H32 and Polyoxymethylene is explored experimentally in the paper. The failure mechanism of stepped clinched joints is studied at both macroscopic and microscopic levels. Increasing the forming force assists in increasing mechanical strength and improving cross-sectional geometry. The optimal energy absorption values and shear strength of 5.038 J and 2040 N were obtained in the experiments when the forming force was 32 kN.

Failure mechanisms of hybrid metal–composite joints with different protrusion densities under a tensile load

The mechanical behaviors of hybrid metal–composite joints with different protrusion densities were investigated by combining numerical and experimental methods. High-fidelity finite element models that considered the failure modes of all components were developed, and specimens based on metal additive manufacturing technology were tested under quasi-static tensile load to verify the numerical calculations. The results showed that the load capacity and the dominant fracture mode of joints were significantly affected by the metal protrusion density. The failure mechanisms of joints under different protrusion conditions exhibited a clear difference, which proved the possibility of an optimal and functional joint design.

Investigation of the failure mechanism of dissimilar resistance spot welding of steels

Austenitic and duplex stainless steels are majorly preferred for heat exchangers and chemical containers. This research work investigated the failure mechanism of dissimilar welded joints of AISI 347 and DSS 2205. The welded specimens were investigated using tensile shear tests, cross-tension tests, coach peel tests and microhardness tests. The specimen absorbed a maximum tensile shear load of 18 kN during the tensile shear test, and the failure mode was button pull-out with brittle fracture. The test sample absorbed a load of 15.1 kN during the cross-tension test, and the failure mode was button pull-out with brittle fracture. During the coach peel test, the sample absorbed a maximum load of 4 kN and ductile fracture was observed at the vicinity of the nugget. The failure mode in the coach peel test was of button pull-out type. The microhardness test recorded a maximum hardness of 312.8 HV, which is 78.74 and 7.1% higher than the base metal hardness values of AISI 347 and AISI 2205, respectively. The specimen failed under pull-out failure mode in all the tests, and hence, the weld zone was intact in all specimen arrangements and loading conditions.

Damage Analysis of CFRP Hybrid Bonded-Bolted Joint during Insertion of Interference-Fit Bolt.

In this study, experiments and finite element analysis (FEA) were used to evaluate the impact of interference-fit sizes on CFRP hybrid bonded-bolted (HBB) joint damage during bolt insertion. The specimens were designed in accordance with the ASTM D5961 standard and bolt insertion tests were performed at selected interference-fit sizes (0.4%, 0.6%, 0.8%, and 1%). Damage to composite laminates was predicted using the Shokrieh-Hashin criterion and Tan's degradation rule via the user subroutine USDFLD, while damage to the adhesive layer was simulated by the Cohesive Zone Model (CZM). The corresponding bolt insertion tests were performed. The variation of insertion force with interference-fit size was discussed. The results showed that matrix compressive failure was the main failure mode. With the growth of the interference-fit size, more failure modes appeared, and the failure region expanded. Regarding the adhesive layer, it did not completely fail at the four interference-fit sizes. This paper will be helpful in designing composite joint structures and especially for understanding CFRP HBB joint damage and failure mechanisms.

Effect of edge riveting on the failure mechanism and mechanical properties of self-piercing riveted aluminium joints

In order to improve the use of aluminium alloys in lightweight automotive body panels, the failure mechanism and mechanical properties of AA5052 aluminium alloy sheets under different conditions were investigated by means of self-piercing riveting (SPR). The impact of riveting position on the structural strength, absorbed energy and instantaneous stiffness of self-piercing riveted connections was analyzed using the edge riveting method. Four edge distances of 1.65 mm, 2.65 mm, 3.65 mm and 4.65 mm were considered for the experimental study, and the riveted structure was analyzed and tensile shear tests were carried out by comparing the mechanical properties. The results indicated that this riveting method changed the failure mode of the joint, with the rivet pulling out from the lower sheet to a co-existence of rivet pull-out and riveted mouth sheet breakage; the maximum shear load, absorbed energy and deformation resistance decreased as the distance from the riveting point to the strip edge decreased; and the strength of the riveted joint based on the upper plate was significantly greater than that based on the bottom plate at the same edge pitch, and the stability of the joint is superior. This study provides a theoretical basis for the damage suppression of aluminium alloy edge riveted joints and the lightweight production of vehicles.

Research on the joining of aluminum alloy and high-strength steel by dieless clinched-adhesive processes

Aluminum and high-strength steel are the best choices for modern cars due to their excellent ratio of strength to weight. As application support, the clinched-adhesive process for aluminum alloys and high-strength steels is also attracting increasingly attention. In this paper, a novel dieless clinched-adhesive process was proposed, which greatly improves the joint strength. It also has unique advantages such as low alignment requirements and low joint bulge due to the use of dieless clinched mould. In the background of automotive light weighting, this joining technology has great prospects for development and application due to its many advantages. Meanwhile, the geometric and mechanical characteristics of various material types of clinched-adhesive joints and clinched joints were analyzed. The key geometric parameters, static strength, and absorbed energy of the joints were obtained. Besides, the microscopic/macroscopic failure mechanisms of joints were investigated. The results showed that the shear strength and energy absorption of the clinched-adhesive joints were much higher than the clinched joints. The highest shear strength of 8159.7 N was obtained for the AL5052-AL5052 material combination, which was 298.3% enhanced compared with the clinched joints. The enhancement of the joint strength was mainly caused by the adhesive. Additionally, the macroscopic failure modes of clinched-adhesive joints and clinched joints with the same material combination are identical, but there are some differences in the microscopic failure mechanisms.

An establishing method for worn tubing joint model and the influence of wear on stress distribution of joint sealing surface

Wear has serious influence on the strength and tightness of tubing joint. In this paper, a new joint wear establishment method, “numerical cutting method,” was proposed and the stress distribution characteristics of sealing surface were analyzed. The three-dimensional modeling of a worn tubing joint under complex loads was successfully established and the finite element method was used to calculate the stress distribution on sealing surface. The influence of internal wear on the stress distribution of the sealing surface was analyzed and the failure mechanism of a worn tubing joint was revealed. The results showed that the contact stress of the worn part of the sealing surface decreases with increased wear depth of internal wear. When the internal wear depth reaches 3.0 mm, the maximum contact stress in the worn area decreases by 35.5% than that of the unworn joint along the axial direction and by 27.3% along the circumferential direction of sealing surface. While when the external wear reaches 3.0 mm, the stress distribution of the sealing surface is similar to that of the unworn joint. These mean that more attention should be paid to the prevention of internal wear during operation because an internal wear has more effect on the stress characteristics of the sealing surface than external wear. The sealing belt is located in the middle of the sealing surface, and the width of the sealing belt at different wear depths is roughly the same for two wear forms. This is beneficial to ensure the seal integrity of tubing joint.

Mechanical characteristic and failure mechanism of joint with composite sucker rod

Composite sucker rods are widely used in oil fields because of light weight, high strength, and corrosion resistance. Bonded technology becomes the primary connection method of composites. However, the joints with composite sucker rods are prone to debone and fracture. The connected characteristics are less considered, so the failure mechanism of the joint is still unclear. Based on the cohesive zone model (CZM) and the Johnson-Cook constitutive model, a novel full-scale numerical model of the joint with composite sucker rod was established, and verified by pull-out experiments. The mechanical properties and slip characteristics of the joint were studied, and the damaged procession of the joint was explored. The results showed that: a) the numerical model was in good agreement with the experimental results, and the error is within 5%; b) the von Mises stress, shear stress, and interface stress distributed symmetrically along the circumferential path increased gradually from the fixed end to the loading end; c) the first-bonded interface near the loading end was damaged at first, followed by debonding of the second-bonded interface, leading to the complete shear fracture of the epoxy, and resulted in the debonding of the joint with composite sucker rod, which can provide a theoretical basis for the structural design and optimization of the joint.

Rotational performance of semi-rigid plate-type joints for reticulated shell structures composed of plate members

Manufactured by laser cutting technology with planar steel plates, the plate members have significant advantages in efficiency, customization, and transportation. These advantages make the plate members suitable for building small or medium-span curved reticulated shell structures. The plate members have been adopted in a novel reticulated shell structure with stiffening methods for resolving local buckling issues. In this type of structure, the semi-rigid plate-type joints are used to connect plate members. The previous study indicated that the rotational stiffness of plate-type joints has a great impact on structural stability. To investigate the rotational performance of the semi-rigid plate-type joints, a comprehensive study has been conducted in this research. Experimental tests were performed on a total of 12 specimens to obtain the moment-rotation responses of the joints. Four phases of the failure process were observed in the tests, namely, the linear elastic phase, slipping phase, hardening phase, and failure phase. The influences of joint width, joint thickness, and bolt diameter on the rotational performance are revealed by the experiments. Then, a refined finite element (FE) model was built and validated by the experimental results. This validated FE model clarified the failure mechanism of joints from the perspective of stress development and contact condition. Furthermore, theoretical formulas were established to calculate the key characteristics of the moment-rotation response, which is proved to have acceptable accuracy in predicting the rotational performance of joints. The conclusions of this study may provide a valuable reference for the structural stability design of reticulated shell structures composed of plate members.

Effect of Geometry and Orientation on the Tensile Properties and Failure Mechanisms of Compliant Suture Joints.

Compliant sutures surrounded by stiff matrices are present in biological armors and carapaces, providing enhanced mechanical performance. Understanding the mechanisms through which these sutured composites achieve outstanding properties is key to developing engineering materials with improved strength and toughness. This article studies the impact of suture geometry and load direction on the performance of suture joints using a two-stage reactive polymer resin that enables facile photopatterning of mechanical heterogeneity within a single polymer network. Compliant sinusoidal sutures with varying geometries are photopatterned into stiff matrices, generating a modulus contrast of 2 orders of magnitude. Empirical relationships are developed connecting suture wavelength and amplitude to composite performance under parallel and perpendicular loading conditions. Results indicate that a greater suture interdigitation broadly improves composite performance when loading is applied perpendicular to suture joints but has deleterious effects when loading is applied parallel to the joint. Investigations into the failure mechanisms under perpendicular loading highlight the interplay between suture geometry and crack growth stability after damage initiation occurs. Our findings could enable a framework for engineering composites and bio-inspired structures in the future.

Investigation on the transitional micromechanical response of hybrid composite adhesive joints by a novel adaptive DEM model

This work developed a discrete element model to adaptively capture the transitional micromechanical response and failure mode of adhesive joints with dissimilar adherend materials and different configurations. Especially, the development of the model only requires one-time calibration. Loctite EA 9497 epoxy adhesive, aluminium (AL) and polyphthalamide (PPA) were selected to make different types of hybrid adhesive joints for the lab tests. The modelling applicability in simulating Mode I, Mode II cohesive failure and adhesive, mixed failure modes was subsequently validated with the experimental data. The validation shows that the proposed model can accurately capture the observed failure modes and joint performances. It is followed by investigating the ability to adaptively obtain the variation of fracture energies with different adhesive thicknesses. The results agree well with the current reports on the growth trend of fracture energies which see a rise till the thickness reaching 0.8 mm and subsequently decline to a plateau. Finally, key factors including the adhesive thickness, lap length were selected to perform a parametric study to investigate their influences on the failure mechanism and micromechanical response of hybrid joints. It is found that a thickness range of 0.1–0.3 mm is adequate to obtain satisfactory joint strength whilst thicker adhesive over 0.6 mm will decrease the joint strength. This is due to that a thinner adhesive layer can facilitate its cohesive fractures and thus fully use the resistance of adhesive. A range of lap length from 6 mm to 12.5 mm was found to have a higher efficiency of improving the joint strength when AL adherend was used.

Fatigue Failure Mechanism of Adhesive Joints Treated by Laser Patterning Surface Treatment

Fatigue Failure Mechanism of Adhesive Joints Treated by Laser Patterning Surface Treatment

Experimental study on re-centering behavior and energy dissipation capacity of prefabricated concrete frame joints with shape memory alloy bars and engineered cementitious composites

To enhance the seismic performance of prefabricated concrete frame joints, an innovative prefabricated beam-column joint with shape memory alloy (SMA) and engineered cementitious composite (ECC) materials was proposed in this paper. Four 1/2-scale test specimens, including one SMA–ECC prefabricated beam-column joint and three comparison joints (namely particularly reinforced concrete cast in situ joint, ordinary concrete prefabricated joint, and ECC-reinforced prefabricated joint) were designed and fabricated. A new type of semi-mechanical sleeve connector was designed to link the SMA bar with the longitudinal reinforcement of the precast beam. Through the low-cycle reciprocating loading tests on the specimens, the failure mechanism, bearing capacity, and self-centering performance of each frame joint were studied. The results show that post-pouring ECC in the plastic hinge zone of beam-column joints can significantly improve the cracking failure form and the ductility of the joints. Though the initial stiffness and energy dissipation capacity of the structure are slightly reduced when SMA and ECC are applied to the prefabricated beam-column joints. Nevertheless, the new composite materials can significantly enhance the ductility and self-centering capacity, reduce the residual deformation and the stiffness degradation rate of the structure. The SMA–ECC reinforced prefabricated beam-column joint can achieve better functional self-resilience ability after earthquake.

Analysis of failure mechanisms of adhesive joints modified by a novel additive manufacturing-assisted method

The research presented in this paper used an innovative method to modify the configuration of adhesively bonded joints for improved mechanical performance. Additive manufacturing was employed to produce sacrificial support structures with a water-soluble filament (Polyvinyl Alcohol). The design freedom offered by additive manufacturing makes it easy to tailor fixtures to any geometry, which can be used to accurately make the desired fillet shape at the end of the adhesive bond line. In addition to the experimental tests, the finite element method (FEM) was used to study the stress distribution along the bond line for four different modified bonded joints, whilst the discrete element method (DEM) was used to estimate the joint failure load and crack path in the adhesive bond line due to its strength in describing the initiation and progression of micro-cracks. The results show that the novel manufacturing method can produce an accurate fillet at the end of the bond line, regardless of the adhesive type. The mechanical performance of the joints with the modified features increased significantly. Furthermore, the failure load and crack path obtained from the DEM model is in close agreement with experimental and finite element (FE) results. Hence, the failure mechanism of the hybrid joints is then summarised.

Effects of microstructure heterogeneity on tensile properties and failure mechanism of GTAW joint of as-cast Ti2531

In this study, as-cast dual-phase titanium alloy Ti2531 was welded by Gas Tungsten Arc Welding, and the effects of microstructure heterogeneity on tensile properties and failure mechanism was analyzed. Tensile test results showed that the specimens fractured in the base metal region, and the tensile strength R m of the welded plate was 855 MPa ~ 859 MPa, which was almost the same as that of the base metal. It was found that, compared with the base metal region, the fine and basketweave phase in the weld zone and heat-affected zone resulted in higher hardness and yield strength. Therefore, plastic strain concentration occurred in the base metal region and a large number of kink bands were found, which accounts for the relatively good plasticity with the fracture strain of 0.073–0.09. In addition, by means of intergranular orientation analysis, it was demonstrated that [0001] α and [101] β were the rotation axes of kink bands in the α and β phases, respectively. Furthermore, by observing the high-resolution electron microscopy, it was found that these kink bands were formed by the arrangement of edge dislocations. As a consequence, when the lattice distortion was severe, the unstable expansion of kink bands occurred and cracks were formed in widmanstätten colonies, inducing the failure of the specimen in the base metal region and great tensile strength equivalent to that of base material. • The weld joint of Ti2531 had good tensile strength close to that of base material. • Plastic deformation was concentrated in base metal region rather than other regions. • Kink bands were formed to coordinate severe plastic deformation in base metal region. • The instable expansion of kink bands resulted in the fracture of the welded specimen.

Study on the mechanical properties and fatigue failure mechanism of 7075-T6 aluminum alloy joints under different joining processes

To obtain the theoretical basis and reference basis for the selection of low ductility aluminum alloy joining methods, three kinds of joints were obtained using 7075-T6 aluminum alloy sheets for clinching, self-piercing riveting (SPR), and resistance spot welding (RSW) joints, and the single-lap shear tests were performed on the three kinds of joints, and fatigue tests were conducted on the clinched joints and SPR joints. The fatigue fracture of the SPR joint was analyzed using scanning electron microscopy (SEM) and X-ray energy-dispersive spectroscopy (EDS). The results showed that the SPR joint demonstrated the best static performance, followed by the clinched joint and the RSW joint. In the case of the fatigue test, the SPR joint showed better fatigue performance than that of the clinched joint. The fatigue failure of the SPR joint and clinched joint is associated with fretting wear. Fretting wear of the SPR joint is more severe than that of the clinched joint. The debris produced by fretting led to microcracking phenomena in the plate. Under the action of alternating load, the microcracks continued to expand and generate macrocracks, and the joint was broken and finally failed. This fretting wear is the root cause of the failure of the SPR joint. Thus, the SPR joints exhibited the best mechanical properties.

Effects of different design factors on the shear performance of assembled steel–concrete composite beam with local laminated joint

This paper aims to experimentally investigate the effects of constructional details on the shear resistance of assembled steel–concrete composite beam with the local laminated joint. A series of push-out experiments were carried out to clarify the key structural factors determining the shear behavior and failure mechanism of post-cast wet joints under the combined action of the longitudinal loading and bending loading. Results indicated that the anchorage length of bottom transverse reinforcement placed in the post-pouring region had a significant impact on the shear resistance of assembled concrete slab, especially the ultimate bearing capacity and ductility of push-out specimens decreased when the anchorage length decreased to a critical value. In addition, using the U-type bottom transverse reinforcement could optimize the size of reserved slots, but this method presented a poor performance in limiting the cracking and failure behaviors of assembled slabs. Compared with the surface roughness treatment of the prefabricated concrete slab, the steel bar truss applied in the local laminated part could effectively strengthen the interface bond strength between the precast concrete and post-cast concrete, avoiding the premature cracking phenomenon. Furthermore, the reasonable layout of bottom transverse reinforcements could make full use of the plastic properties of steel bars and increase the shear resistance of assembled concrete slab, but the plastic deformation of steel bars might lead to the crushing of the post-cast concrete near the interface between the precast concrete and post-cast concrete. Finally, discussing the change of stress distribution on the section of post-cast wet joints caused by the negative bending moment based on the failure analyses, and the formulas of the shear capacity of local laminated joints considering the effects of the negative moment and constructional details were established.

Effects of Mode Mixity on the Failure Mechanism of Aged Adhesive Joints

The strength and the performance of adhesive joints can be significantly influenced by the ageing procedure. However, the role of aging in the failure mechanism of adhesive joints as a function of loading conditions has not been studied yet. The current research aims to investigate the effect of mode mixity on the failure mechanism of aged adhesive joints using Arcan samples. Based on the results loading the tested joints in shear led to a higher percentage of interfacial failure than in tensile. However, it was also found that the shear loading mode is less sensitive (compared to tensile loading) to the ageing conditions.

Experimental and Numerical Investigation on Seismic Performance of RC Exterior Beam-Column Joints with Slabs

The effect of a cast-in-place slab on the beam-column joint at beam ends in reinforced concrete (RC) structures under earthquake attacks has not been fully understood, and therefore, it is not manifestly addressed to some of the design criteria or specifications. Consequently, the contribution of slab to the seismic resistance of structures is often ignored or just included in an approximate manner. In this study, the experiment of two 1/2-scaled exterior beam-column joints without slabs and three 1/2-scaled joints with slabs under the combination of quasi-static repeated cyclic loading and constant axial force was carried out to investigate the effect of the cast-in-place slab on the seismic performance of exterior beam-column joints. The results show that for specimens EBCJ1 and EBCJ2 without slab, the decline was approximately 5%, while for specimens EBCSJ1 and EBCSJ3, the decline in the load is obvious and approximately more than 10%. For specimen EBCSJ2, which exhibited a slightly different behavior in the hysteresis curves, the maximum carrying capacity reached at the displacement of 70 mm during the first cycle. The cast-in-place slab has different effects on the failure mechanism and load transfer mechanism of the exterior beam-column joint, which depends on the column-beam moment strength ratio in the loading protocol. The slab has a positive effect on the energy dissipation capacity of the joint but has a negative effect on the load carrying capacity. In addition, finite element (FE) analysis of the tested specimens was conducted. The FE numerical models were established based on the construction information and loading conditions from the experiment and then validated by comparing them with the experimental observation.