Tensile Failure Load Research Articles

Investigating fabric interlayer effects on tensile loading limits of adhesively bonded single-lap composite joints

This paper investigates enhancing the effectiveness of glass fiber/epoxy composite single-lap bonded joints by using fabric interlayers between the adherends. It was aimed to evaluate the changes in the joint tensile strength depending on the parameters such as different interlayer fabric types (S2-glass fabric and Kevlar fabric), numbers of interlayers (0, 1, 2, and 3), clamping pressure (0, 4, and 6 MPa), and temperature (20, 55, and 80°C) applied to the joint region throughout the curing period. Significant enhancements in peak tensile forces were observed by varying these parameters. The most substantial increase in tensile properties was achieved for the joint with two-layer S2 fabric fabricated at 4 MPa pressure and 55°C curing temperature, denoted as “2L-S2-P4-T55.” Compared to a non-layered joint, those with 1, 2, and 3 S2 fabric interlayers exhibited 35.5%, 39.6%, and 45.2% increases in tensile peak force, respectively. Increasing bonding pressure from 0 MPa to 4 MPa resulted in a 5.2% tensile failure load increase for double S2 fabric interlayered joints cured at 20°C, but a 6.7% decrease at 6 MPa. Using one-layer Kevlar fabric instead of one-layer S2 fabric caused a 15.2% drop in tensile peak force, still 14.9% higher than the non-layered joint.

Vine copulas for accelerated prediction of composite strength variability

Composite materials are essential for many advanced engineering applications, but numerical quantification of strength variability can be computationally expensive. This paper proposes a novel methodology that drastically reduces the number of finite element simulations required to characterise composite material strength variability using the concept of vine copulas. This concept provides a flexible tool for the representation of high-dimensional dependencies. The methodology considers spatial scatter of three material variabilities: fibre volume fraction, fibre misalignment and fibre strength. First, the cross-correlation between stress, fibre volume fraction and fibre misalignment is fitted by a vine copula using results from a limited number of finite element simulations. Next, the vine copula is used to predict new conditional stress realisations when given realisations for the fibre volume fraction and fibre misalignment. This effectively replaces the finite element simulations with a vine copula that is much faster to evaluate. The methodology is verified by predicting the tensile failure load of a unidirectional composite coupon. Predictions are very similar to an exclusively finite element-based approach, while reducing the number of finite element simulations by a factor of 200.

Effect of ultrasonic amplitude and riveting speed on mechanical properties of Ti-45Nb riveted lap joints

Ultrasonic vibration-assisted machining has been introduced as a new process in riveting aircraft components. In this paper, the effects of different ultrasonic amplitudes and riveting speeds on the quality, shear properties, and cross-tension properties of riveted joints are investigated. The failure sample fracture was characterized using a scanning electron microscope and the cause of the fracture was discussed. The results show that the ultrasonic amplitude is negatively correlated with the height of the riveted joint and positively correlated with the diameter of the riveted joint. The maximum shear failure load was obtained at a riveting speed of 5 mm/s with an ultrasonic amplitude of 35.3 μm, and the maximum cross tensile failure load was obtained at an ultrasonic amplitude of 23.3 μm. All shear fractures occurred in the rivet shanks and all cross fractures occurred in the rivet manufactured head, and the failure modes of both shear and cross-tension fracture were mixed brittle and plastic fracture modes.

Formation mechanisms and mechanical properties in aluminum cables and copper terminals ultrasonic welded joint

To fabricate highly reliable Al cables/Cu terminals components and elucidate the microstructure evolution of the joint during ultrasonic welding, ultrasonically welded structures of 50 mm2 Al cables and 2 mm-thick copper terminals were conducted at welding energies from 1200 J to 2800 J and an amplitude of 54.6 μm in this paper. As the welding energy increased, the degree of plastic deformation of the Al wires gradually increased, the microstructure of the Cu side remained basically unchanged, and the effective contact area of the Cu/Al interface was gradually enlarged, enhancing the coherence between the Al wires, and the Cu-Al interfacial structure changed from an unbonded area to continuous mechanical interlocking. Parallelly, the Al grains transformed from fine serrated to equiaxed and lamellar crystals driven by geometric dynamic recrystallization (GDRX), continuous dynamic recrystallization (CDRX), and dynamic recovery (DRV), forming distinct shear textures of B/B̅{111}<110>, Rt Goss{110}<110>, Rt Cube{001}<110> and the recrystallization texture F{111}<112>, and the content of shear textures increased from 2.9% to 17.4%. In addition, the tensile shear failure load of the joint reached 2962 N, which met the requirements of cable installations in the field of new energy vehicles (>1650 N). Fracture analysis showed the fracture location transitioned from the Cu-Al interface to the Al-Al interface with an increase in welding energy from 1600 to 2400 J. This work has theoretical guidance for the continuous promotion of vehicle light-weighting.

Comparative assessment of failure in single shear lap joints fabricated using various joining techniques

The current research endeavour reports the performance of single shear lap joints of flax/PP composite laminates. The joints were fabricated using mechanical joining, fusion bonding (ultrasonic and hot plate joining), and hybrid joining techniques (mechanical/ultrasonic joining and mechanical/hot plate joining). In case of the mechanical and hybrid joining, the effect of the bolt size, and number of bolts (single and double) on the tensile failure load was investigated. Pertaining to mechanical joining, the large bolt size and double bolts recorded higher tensile failure load compared to smaller bolt size and single bolt, respectively. Whereas with double bolts, no increase in the tensile failure load was observed for the hybrid joints, due to reduction in bonded area. The hybrid joints (mechanical/ultrasonic) recorded the maximum tensile failure load compared to all other type of joints. The load-extension behaviour and failure of joints was also examined. Expect mechanical joints, all other joints exhibited structural type of failure. In contrast, the mechanical joints resulted in a net-tension failure mode with failure line passing through the hole. However, the thermal decomposition and crystalline behaviour (XRD spectra) of developed joints did not vary significantly. The morphology of failed joints was examined using scanning electron microscope.

Biocomposite Anchors Have Greater Yield Load and Energy Compared With All-Suture Anchors in an In Vitro Ovine Infraspinatus Tendon Repair Model

PurposeTo compare tensile fatigue and strength measures of biocomposite and all-suture anchors in an ovine humerus-infraspinatus tendon model of rotator cuff repair. MethodsInfraspinatus tendons on adult ovine humeri were sharply transected at the insertion. One of each pair was randomly assigned for fixation with two biocomposite or all-suture anchors. Constructs were tested with 200 cycles of 20-70 N tensile load and gap formation was measured at the incised tendon end every 50 cycles. They were subsequently tested to failure. Outcome measures including fatigue stiffness, hysteresis, creep and gap formation, and tensile stiffness, and yield and failure displacement, load, and energy were compared between anchors. ResultsBiocomposite anchors had higher yield load (134.1 ± 6.5 N, p<.01) and energy (228.6 ± 85.7 J, p<.03) than all-suture anchors (104.7 ± 6.5 N, 169.8 ± 85.7 J). Fatigue properties were not different between anchors, but stiffness and gap formation increased and hysteresis and creep decreased significantly with increasing cycle number. ConclusionsWhile the yield displacement of both anchors was within the range of clinical failure, the tensile yield load and energy of ovine infraspinatus tendons secured to the humerus with two single-loaded all-suture anchors in a single row were significantly lower than those secured with two biocomposite anchors in the same configuration. Clinical RelevanceIt is important to understand the biomechanical properties for selecting anchors for rotator cuff repair. A direct comparison of fatigue testing followed by failure strength of infraspinatus tendon fixation with all-suture and biocomposite anchors could help guide anchor selection and post-operative mobility recommendations.

A comparative study on resistance spot and laser beam spot welding of ultra-high strength steel for automotive applications

In this study, the effect of resistance spot welding (RSW) and laser beam spot welding (LBSW) processes on evolution of microstructure, load endurance capabilities, heat affected zone (HAZ) softening, and corrosion resistance of ultra-high-strength (UHSS) steel joints welded in lap joint design is investigated. The UHSS sheets of dual phase 1000 grade (UHSDP1000) having 1.20 mm thickness were joined using the RSW and LBSW parameters optimized by response surface methodology (RSM). The microstructural features of welding regions of RSW and LBSW joints were studied using optical microscopy (OM). The load endurance capabilities of RSW and LBSW joints were assessed using the tensile shear failure load (TSFL) and cross-tensile failure load (CTFL) tests. The ruptured surfaces of TSFL and CTFL tested samples were examined utilizing scanning electron microscopy (SEM). The microhardness distribution of divergent regions of RSW and LBSW joints was evaluated and imputed to the TSFL and CTFL failure of joints. The corrosion resistance of RSW and LBSW joints was analyzed using potentiodynamic corrosion and immersion corrosion tests. The RSW joints showed 183% and 62.79% greater TSFL and CTFL endurance capabilities than LBSW joints. The TSFL and CTFL endurance capabilities of LBSW joints are inferior to RSW joints due to the smaller load bearing area. It causes the stress concentration in FZ and HAZ of LBSW joints. The RSW joints and LBSW joints disclosed TSFL and CTFL failure in button pull out rupture mode with tearing of HAZ. The failure of RSW and LBSW joints in HAZ is due to the softening caused by martensitic tempering and coarsening of grains. The LBSW joints disclosed inferior resistance to corrosion than RSW joints due to the higher martensite content which contributes to greater fraction of favorable pitting sites and decreased corrosion resistance.

Microstructure and mechanical properties of Al-Zn-Mg-Cu alloy joints welded by ultrasonic spot welding with soft specification

The high-strength lightweight Al-Zn-Mg-Cu alloy sheets were welded using ultrasonic spot welding with soft specification. The peak tensile shear failure load reached 7.3 kN, which satisfies the requirements of AWS D17.2 for spot-welded specimens. This is due to the fact that the material undergoes sufficient plastic deformation during the welding process with soft specification, thereby improving metallurgical bonding. Moreover, the dynamic recrystallization resulting from plastic deformation makes the grain size of the interface significantly refined. The grains with a size of 10 μm in the base metal are transformed into recrystallized grains with a size of 2 μm at most, which is in favor of improving the mechanical properties of the joint. Finally, even under soft specification conditions, excessive welding time can lead to macroscopic damage to the joint, initiation of cracks, and destruction of the grain boundary structure.

An evaluation model of bearing capacity for CFRP connection structure with lightning thermal damage

Connection structure of carbon fiber reinforced plastic (CFRP) is fragile to lightning and its damage form is complex. Its bearing capacity is affected, which should be evaluated to ensure safety after lightning strike. Thus, a model of bearing capacity prediction (BCP) is proposed for CFRP connection structure. Its lightning damage is evaluated from thermal perspective combining joule heat and dynamics failure, which is caused by lightning ablation and the Blow-Off Impulse (BOI) effect, respectively. Electrical thermal coupling and high explosive models are utilized for calculation. Subsequently, lightning thermal damage is inherited by full restart method. The computing efficiency and convergence is improved caused by structural local distortion. Tensile bearing capacity of structure is assessed by employing the strain-based 3D Hashin criterion. A tensile experiment is carried out to verify BCP model. The results show that lightning thermal damage is the worst around current injection region. Tensile-shear and extrusion-shear failures concentrate at CFRP fastener holes under tensile load. Tensile failure load of structure is further reduced by 8.03% due to the BOI effect. The bearing capacity of CFRP connection structure can be accurately predicted by BCP model after lightning strike and deviation is 9.8% from experiment.

Quantification of inhomogeneity and anisotropy of bituminous mixtures using biaxial experimental data

Most of the existing mechanical characterization test methods and the analytical models for bituminous mixtures are developed based on the assumption of homogenous and isotropic material properties. However, the extent to which such assumptions hold good for bituminous mixtures is not very clear. A biaxial testing scheme in indirect tension mode can come in handy to collect the experimental data at different test temperature regimes. In this study, a bituminous mixture with a nominal maximum aggregate size (NMAS) of 13.2 mm is used to fabricate cylindrical test specimens with 150 mm diameter and 63.5 mm thickness for conducting the repeated load indirect tension (IDT) test. The input load level is selected as 5 to 13 % of the indirect tensile (ITS) failure load in the form of a haversine pulse of 0.1 s loading and 0.9 s rest period. Such loading is applied on zero-degree and ninety-degree orientations of the specimen. The resulting deformations in different directions are measured using linear variable differential transducers (LVDT) attached to both diametral faces of the specimen. The response of the bituminous mixture specimen is captured at three different temperatures of 20, 25, and 30 °C using two different gauge length (half and quarter gauge of the total diameter). A new framework is introduced in this study to evaluate the extent of inhomogeneity and anisotropy of bituminous mixtures. The deformation response of the test specimen captured in the same orientation at different diametral faces is compared to evaluate the extent of inhomogeneity. The extent of anisotropy is evaluated by comparing the deformation response of the test specimen captured at different orientations within the same diametral face. A 15 % variation in the average peak deformation is chosen as the demarcation for determining the extent of inhomogeneity and anisotropy. From this investigation, it is observed that half gauge length experimental data exhibits homogenous and isotropic behavior for all three test temperatures. The quarter gauge length data exhibit similar behavior at 30 °C, whereas it is observed as homogenous and anisotropic at the other two test temperatures.

Enhancing the mechanical performance of notched glass/epoxy composite laminates via hybridisation with thermoplastic fibres

This study examines empirically and theoretically the open-hole tension and compression characteristics of thermoset composites using hybrid glass/polypropylene and glass/innegra yarns. The Abaqus software, finite element analysis (FEA) has been adopted to predict the tensile and compressive failure loads and damage failure modes for un- and notched samples under tensile and compressive strength tests. The commingling technique was used to create hybrid yarns, which were then transformed into non-crimp preforms before the infusion procedure. It was noticed that the inclusion of thermoplastic polypropylene (PP) and innegra fibres increased the ductility of yarns and composites. Densities of hybrid composites were also reduced by up to 20% when compared to pure glass/epoxy composites. Tensile and open-hole tensile (OHT) test results revealed that hybrid composites are less notch sensitive than glass/epoxy composites due to enhanced composite ductility. For glass composites, having holes resulted in a 41% decrease in tensile strength, compared to reductions of only 25% and 26% for PP and innegra fibre composites, respectively. Further, compression and open-hole compression (OHC) tests presented similar results with OHT tests whilst compressive strength reduction was lower for hybrid composites (10% and 11%) compared to glass/epoxy (28%) ones. The results of the numerical simulation for damage failure modes and tensile and compressive failure loads for un-notch and notched composite laminates are consistent with the experimental findings both qualitatively and quantitatively.

Experimental study on the mechanical properties of three‐dimensional braided composite circular tubes with preembedded licker‐in

AbstractThis study investigates the tensile and compression properties of three‐dimensional five‐direction (3D5D) braided composite circular tubes with preembedded titanium alloy licker‐ins. The influence of the braided angle, braided thickness, and braided configuration on the bearing capacity is analyzed, and the microdamage morphology and failure mechanism of the tube structure are examined using scanning electron microscopy. Results show that the 3D5D braided tube has a larger tensile failure load than the 3D full five‐direction braided tube of the same outer diameter. In circular tubes of the same braided configuration and outer diameter, the compression failure load increases with the wall thickness, and the C‐ø30t3 circular tube achieves the maximum compression failure load. The damage morphology is characterized by the pulling‐off failure of the licker‐in joint. The T‐ø30t2.5 and T‐ø25t3 circular tubes achieve a large failure load, with an average tensile load of over 120 kN. The failure morphology is characterized by the cracking of the fiber at the end of the tube after the licker‐in joint has been pulled off. The average tensile failure load of the T‐ø30t3 circular tubes is over 105 kN, and the failure morphology reveals a broken licker‐in joint, indicating design deficiencies that require further optimization. The findings of this paper can provide an important scientific basis for the lightweight and high‐strength connection design for 3D braided composites in near‐space aerostats and their flight applications.

The Influence of Tool Geometry on the Mechanical Properties and the Microstructure of AA6061-T6 Aluminum Alloy Friction Stir Spot Welding.

In this work, the influence of the tool geometry on friction stir spot welding (FSSW) was studied on sheets made of AA6061-T6 aluminum alloy. Four different AISI H13 tools with simple cylindrical and conical pin profiles and 12 mm and 16 mm shoulder diameters were used to perform the FSSW joints. Sheets of 1.8 mm thickness were used during the experimental work to prepare the lap-shear specimens. The FSSW joints were performed at room temperature. For each joining condition, four specimens were carried out. Three specimens were used to find the value of the average tensile shear failure load (TSFL), while the fourth one was used to examine the micro-Vickers hardness profile and to observe the microstructure of the cross-section of the FSSW joints. The investigation concluded that higher mechanical properties corresponding to the finer microstructure were obtained by the conical pin profile and the higher shoulder diameter compared with the specimens performed using the cylindrical pin tool and lower shoulder diameter due to the higher strain hardening and the higher frictional heat generation, respectively.

Corrosion studies on friction stir spot welded dissimilar AZ31-C27200 Cu joints

In this investigation, corrosion studies were conducted on dissimilar friction stir spot welded AZ31 Mg-C27200 Cu joints using pitting corrosion tests. Mechanical characteristics of the joints were also evaluated. By conducting tensile testing, the tensile shear failure load value of AZ31 Mg-C27200 Cu joints were 62.36% of the value of similar AZ31 Mg – AZ31 Mg joints and 51.9% of the values of C27200 Cu– C27200 Cu joints, respectively. The joint interface hardness of the dissimilar combination such as AZ31 Mg– C27200 Cu joints were 22.03 % and 35.84% greater than the interface hardness values of similar AZ31 Mg–AZ31 Mg and C27200 Cu–C27200 Cu joints, respectively. Bend tests revealed that similar joints broke with interfacial tear and the dissimilar joints broke with nugget pullout. By conducting pitting corrosion tests on the joints, potentiodynamic polarization curves were developed. The corroded samples were subjected to microstructural evaluation using scanning electron microscopy. The variations in corrosion pit density were also identified.

Improved strength of Al-Zn-Mg-Cu alloy USW joints by synchronously applying electropulsing current

The tensile lap shear failure load of Al-Zn-Mg-Cu alloy ultrasonic spot welding joints (2.89 kN) by synchronously applying electropulsing current is significantly improved compared to the traditional joints (0.39 kN). This can be ascribed to the enhancement of interfacial plastic deformation induced by the dissolution of η' phase, which is the combined effect of electropulsing current and ultrasonic vibration.

Effects of Tool Plunging Path on the Welded Joint Properties of Pinless Friction Stir Spot Welding

Four tool plunging paths including a one-time plunging path and three step-by-step plunging paths were designed to study the effects of the tool plunging path on the welded joint properties of pinless friction stir spot welding (PFSSW). The appearance, cross-sectional microstructure, welding temperature, microhardness, and tensile shear failure load of the PFSSW of thin copper sheets under different tool plunging paths were explored. Furthermore, the fracture modes of welded joints under different tool plunging paths were analyzed. Studies showed that path 1 (plunge total depth at one time) produced the largest range of stirring zone, but the grains in the stirring zone were larger and the width of the thermal-mechanical affected zone was smaller. Path 1 obtained the highest peak temperature during the welding process, and path 3 (plunge 1/3 total depth + plunge 2/3 total depth) gained the lowest peak temperature. The greater the initial plunging amount of the tool, the faster the temperature rise rate in the welding stage. The tensile shear failure loads for path 1, path 2 (plunge 1/2 total depth + plunge 1/2 total depth), path 3, and path 4 (plunge 2/3 total depth + plunge 1/3 total depth) were 8.65 kN, 8.15 kN, 8.25 kN, and 8.85 kN, respectively. The tensile shear failure load of path 4 was 2.3% higher than that of path 1. The fracture modes of welded joints under different tool plunging paths were all nugget pullout fractures. The fracture morphology indicated that the fracture type was ductile fracture. The step-by-step plunging path proposed in this work extends the traditional PFSSW process. The findings of this study can provide a reference for the selection and design of tool plunging paths for PFSSW.

Friction stir lap joining techniques effects on microstructure and tensile properties of high-strength automotive steel top hat sections

Dual Phase (DP) steel, a type of Advanced High Strength Steel (AHSS) with a thickness of 1.7 mm, is used to fabricate single-hat components that are then joined to the base plate using two friction stir welding processes: friction stir lap welding (FSLW) and friction stir spot lap welding (FSSLW). It is difficult to join this assembly using fusion welding techniques. The welding variables for the FSLW process, tool rotation speed (TRS), tool traverse speed (TTS), and plunge depth (PD), were optimized using the design of an experiments-based response surface method by experimentally measured tensile shear failure load (TFL) of top hat assembly. For the FSSLW process, the welding variable TTS was replaced by dwell time (DT). Peak temperature, microstructure at different zones, microhardness mapping, and energy absorption capacity of both processes were evaluated under optimal welding conditions. For both processes, the stir zone and the heat-affected zone had the highest and lowest microhardness, which can be correlated with the level of martensite tempering, martensite lath spacing, polygonal ferrite volume, and precipitated carbides. Under optimum welding conditions, the TSL and energy absorption of FSLW joints were 14 kN and 170 J, respectively, which is 20% and 47 higher than the TSL and energy absorption of FSSLW joints.

Large deformation and failure analysis of the corrugated flexible composite skin for morphing wing

The morphing wing has been a research hotspot in the aviation field in recent years, and the flexible skin is one of the most important parts of the morphing wing. The analytical method, experimental method and numerical simulation were employed in this paper to evaluate the tensile behaviour and functional mechanisms of a new corrugated Flexible Composite Skin (FCS). The FCS is composed of two thin-walled curved Fibre-Reinforced-Plastics (FRP) composite shells which can be extended and contracted through pure elastic deformation during the large deformation process. Based on equilibrium equations, classical laminate theory and the maximum stress criterion, the analytical model for predicting the tensile behaviour of the FCS was established. FCS specimens were fabricated using vacuum bag method. Tensile experiments of FCS specimens were performed, and complete tensile load–displacement curves and tensile failure loads were measured. In addition, a Finite Element Model (FEM) was established to predict the tensile behaviour of the FCS. Prediction results using the analytical model and the FEM were compared with experimental results, and the three were in good agreement. Finally, the effect of geometric parameters (i.e. radius of curvature, center angle and thickness) on the tensile behaviour of the FCS was further investigated with the aid of the analytical model. It is shown that geometric parameters are one of the key factors affecting the tensile behaviour of the FCS.

Mechanical properties and failure analysis of refill friction stir spot-welded 5052/2A12 joints

The mechanical properties and failure process of 2 mm-thick 5052 Al and 6 mm-thick 2A12 Al fabricated by refill friction stir spot-welding were investigated. The hooks were bent respectively downwards and upwards at plunge depths smaller and larger than the upper plate thickness. The joint area of the lap interface and bearing thickness of the upper plate were related to the hook direction. The tensile shear failure load was affected by structural characteristics and hardness of the joints. Stress concentration occurred in the hook and strain expanded with the hook during fracture. There were two fracture modes: shear fracture and shear plug fracture, where both cracks passed through the hook and fracture morphology of the hook was less plastic.

Load-carrying capacity of hot-pressed thermoplastic composite joints

Abstract Composite joints have been commonly used in many industries such as aviation, aerospace, and automotive due to their advantages of being light and durable. Internal stresses may occur especially during the service life of these materials and decrease the load-carrying capacity of the joints. In this study, high density polyethylene (HDPE) and glass fiber reinforced polypropylene composite panels are used resorting to different combinations by using hot-pressing method as a single lap joint, and their mechanical properties are investigated under different temperatures, experimentally. Tensile tests were carried out at different temperatures in order to examine the temperature effect on load-carrying capacity of joints. Different bonding types of composites were compared to obtain the optimal joint configurations. The effect of low velocity impact on the failure response of the joints at impact energy levels of 5 and 10 J is also evaluated. From the tensile tests after impact treatment, it was concluded that transverse impact significantly decreased the load-carrying capacity of the single lap thermoplastic joints. Based upon the experimental results, it was concluded that HDPE–HDPE joints demonstrated higher tensile failure loads at 50 °C after transverse impact. Moreover, the tensile strength of all types of configurations decreased with increasing temperature.