Static Failure Load Research Articles

Fatigue Behavior of H-Section Piles under Lateral Loads in Cohesive Soil

Most structures supporting solar panels are found on thin-walled metal piles partially driven into the ground, optimizing costs and construction time. These pile foundations are subjected to repetitive lateral loads from various external forces, such as wind, which can compromise the integrity of the pile-soil system. Given that the expected operational lifespan of photovoltaic solar plants is generally 20–30 years, predicting their service life under fatigue loads is crucial. This research analyzes the response of H-section piles to lateral fatigue loads in cohesive rigid soils through four field tests, subjected to load cycles of 55%, 72%, and 77% of the static failure load, corresponding to maximum loads of 25 kN, 32 kN, and 35 kN, respectively. Additionally, the effect of load cycles on the degradation of pile-soil adhesion is studied through two pull-out tests following cyclic tests. This study reveals that soil fatigue does not occur under repetitive loads and that soil stiffness remains constant once the cycles causing soil compaction have been overcome. Nevertheless, the accumulated plastic deflection of the soil increases steadily once soil compaction occurs due to cyclic loading. The implications of these results on the fatigue life of photovoltaic solar panel foundations are discussed.

The Response of Reinforced Concrete Composite Beams Reinforced with Pultruded GFRP to Repeated Loads

This paper investigates the experimental response of composite reinforced concrete with GFRP and steel I-sections under limited cycles of repeated load. The practical work included testing four beams. A reference beam, two composite beams with pultruded GFRP I-sections, and a composite beam with a steel I-beam were subjected to repeated loading. The repeated loading test started by loading gradually up to a maximum of 75% of the ultimate static failure load for five loading and unloading cycles. After that, the specimens were reloaded gradually until failure. All test specimens were tested under a three-point load. Experimental results showed that the ductility index increased for the composite beams relative to the reference specimen by 156.2% for a composite beam with GFRP with shear connectors, 148.6% for composite beams with GFRP without connectors, and 96% for the composite beam with a steel I-section.

Experimental study on mixing ratio effect of hybrid graphene nanoplatelet/nano-silica reinforcement on the static and fatigue life of aluminum-to-GFRP bonded joints under four-point bending

In the scenario of nanoparticle-reinforcement, synergistic effect of adding two or more nanoparticles types to the adhesive can be introduced as a solution to achieve more efficient bonded joints. This paper aims to investigate the influence of hybrid insertion of graphene nanoplatelet (GNP) and silica nanoparticle (SNP) additives with various GNP + SNP mixing ratios on the static strength, endurance, and crack initiation life of aluminum-to-GFRP bonded joints under four-point bending. Four specimen groups were prepared: I) neat, II) hybrid-type reinforcements with different mixing ratios of 30 %GNP + 70 %SNP, III) 50 %GNP + 70 %SNP, and IV) 70 %GNP + 30 %SNP. Static tests indicated that, for 0.5 and 1.0 wt%, 70 %GNP + 30 %SNP had the maximum average static failure load, while, for 1.5 wt%, 30 %GNP + 70 %SNP resulted in the highest static strength. Under a fatigue load of 50 %, the longest endurance and crack initiation life was obtained for 70 %GNP + 30 %SNP hybrid-reinforced group. However, under higher fatigue loads of 70 %, variations in hybrid mixing ratio had a negligible effect on crack initiation phase for 0.5 and 1.0 wt%. Under fatigue loads of 70 % and 1.5 wt%, 30 %GNP + 70 %SNP group had 3.4 % and 2.6 %, and 5.1 % longer crack initiation life than 50 %GNP + 50 %SNP and 70 %GNP + 30 %SNP groups, respectively. Finally, major microstructural reinforcing mechanisms were interpreted using scanning electron microscopy (SEM).

Investigating on the influence of multi‐walled carbon nanotube and graphene nanoplatelet additives on residual strength of bonded joints subjected to partial fatigue loading

AbstractAdhesively bonded joints in engineering structures, especially automotive body structures, inevitably experience long or limited fatigue loading conditions. In this article, the shear strength of steel bonded lap joints reinforced by multi‐walled carbon nanotube (MWCNT) and graphene nanoplatelet (GNP) were evaluated after being subjected to limited fatigue loading cycles. For this purpose, three specimen groups of neat, MWCNT, and GNP‐reinforced joints (with 0.2, 0.5, 1.0, and 2.0 wt% contents) were prepared. After performing the static lap shear tests, fatigue testing of each specimen group was conducted under a maximum fatigue load of 50% of its average static failure load until complete separation of the substrates. Accordingly, limited fatigue loadings were applied to each specimen group for 30%, 50%, and 70% of its total fatigue life, and subsequently, a second‐round static testing was performed to evaluate the residual strength of the joints. The results revealed that the maximum static shear strength improvements of MWCNT and GNP‐reinforced joints were associated with incorporating 1.0 and 0.5 wt% particle contents. Moreover, for 0.2 and 0.5 wt% contents, the static strength of the joints reinforced by GNPs was 3.4% and 3.9% greater than that of MWCNTs reinforced joints. On the contrary, for 1.0 and 2.0 wt% filler contents, specimens including MWCNTs had 9.1% and 18.6% higher strength than GNP‐reinforced ones. The highest fatigue life enhancements of 34.1% and 31% were obtained by adding 1.0 and 0.5 wt.% of MWCNT and GNP particles to the adhesive, respectively. It was concluded that, for 0.2 and 0.5 wt% contents, nanoparticle type did not have a noticeable effect on the residual strength of the joints after being subjected to fatigue loading for 30% of its total life. The specimens subjected to 50% and 70% of their total fatigue life indicated a minimum loss in the shear strength for the joints reinforced by dispersing 1.0 wt% of MWCNTs.

An investigation on static and fatigue life evaluation of grooved adhesively bonded T-joints

Adhesively bonded joints with T-shaped configurations are widely used in bonded components of engineering structures used in industries such as automotive, aircraft, and marine. In this paper, static strength and fatigue life of two T-joint configurations of flat and grooved types were evaluated. For this purpose, firstly, the effect of the specimen configuration of the bonded T-joints on the stress field has been calculated using the finite element method. For this purpose, a three-dimensional elastoplastic model is used for simulation. Then, static failure load of these joint types was examined under four loading rates of 1, 10, 50, and 100 mm/min. Also, fatigue tests were performed under maximum fatigue loads of 40%, 60% and 80% of average static failure loads. Results indicated that the average static failure load of grooved specimens was 37.3%, 26.5%, 14.4%, and 9.3% higher than that of the flat type T-joints under 1, 10, 50, and 100 mm/min loading rates, respectively. Moreover, fatigue life cycles of grooved T-joints were 40.2%, 25.3%, and 11.6% longer than that of the flat bonded specimens under 40%, 60%, and 80% maximum fatigue loads, respectively. It was also concluded that, under high fatigue loads, the groove effect can be ignored on improving the fatigue life.

Effect of Loading Angles and Implant Lengths on the Static and Fatigue Fractures of Dental Implants.

Mechanical properties play a key role in the failure of dental implants. Dental implants require fatigue life testing before clinical application, but this process takes a lot of time. This study investigated the effect of various loading angles and implant lengths on the static fracture and fatigue life of dental implants. Implants with lengths of 9 mm and 11 mm were prepared. Static fracture tests and dynamic fatigue life tests were performed under three loading angles (30°, 40°, and 50°), and the level arm and bending moment were measured. After that, the fracture morphology and fracture mode of the implant were observed. The results showed that 9 mm length implants have a higher static failure load and can withstand greater bending moments, while 11 mm length implants have a longer fatigue life. In addition, as the loading angle increases, the static strength and bending moment decrease linearly, and the fatigue life shows an exponential decrease at a rate of three times. Increasing the loading angle reduces the time of the implant fatigue test, which may be an effective method to improve the efficiency of the experiment.

Study on the Effect of Precrack on Specimen Failure Characteristics under Static and Dynamic Loads by Brazilian Split Test

To analyse the dynamic failure characteristics of the rock with a crack in rock engineering, the Brazilian split tests were conducted on the split Hopkinson pressure bar (SHPB) using precrack specimens under dynamic loads. In the study, five groups of different precrack angles are selected; they are 0°, 30°, 45°, 60°, and 90°, respectively. The results show that the static failure load of the specimen as a whole decreases to increase with the growth of the loading angle, and the DIF linear increases with the increase of the loading rate; the failure load of the specimen with an angle of 45° precrack is the most sensitive to the loading rate, followed by 0°, 60°, 30°, and 90°. The crack initiation time of specimen with 30°, 45°, and 60°precrack decreases with the loading rate, while it has no obvious change with the loading rate with 0° and 90°precrack. The failure mode of the specimen was controlled by the stress concentration at the crack tip; the main cracks all point from the crack tip to the loading end. When the precrack and the loading direction are at a certain angle, the failure process will produce secondary cracks; it would be particularly obvious under dynamic load splitting. Once the precrack and the loading direction are at a certain inclination angle, type-II secondary cracks will develop under dynamic load splitting.

A study on the effects of nanostructure reinforcement on the failure load in adhesively bonded joints after the subjected to fully reversed fatigue load

ABSTRACT Today, adhesively bonded joints are frequently used in the space and aviation industries. Joints used in these sectors are generally subject to dynamic loads due to environmental factors. This study experimentally and numerically investigated the static tensile loads of adhesively bonded joints after fully reversed (combination of tensile and compressive) fatigue loading where nanoadhesives – obtained by adding carbon nanostructures into aerospace grade structural adhesive – were used to bond the joints. Single lap joint specimens were produced using a nanocomposite adhesive obtained by adding 1 wt. % graphene, 1 wt. % carbon nanotubes-COOH and 1 wt. % fullerene C60 nanostructures to a DP460 structural adhesive. AA2024-T3 aluminum alloy and carbon fiber-reinforced composites (CFRCs) with a plain weave fabric (0/90°) were used as adherend materials. First, static tensile tests were applied to these joints to obtain their failure loads and then fully reversed sinusoidal fatigue tests were applied under a constant load amplitude, a frequency of 20 Hz and a load ratio of R = −1. Considering the failure loads obtained from the static tensile tests, 106 fully reversed fatigue loading cycles were applied – which was accepted as an infinite life – at 400 N, 800 N and 1200 N load levels. The static tensile failure loads and energy values absorbed of these joints were obtained and the change in the failure loads and energy values absorbed of the joints subjected to fatigue was investigated. The static failure loads of aluminum joints bonded with nanoadhesive and subjected to fully reversed fatigue loading increased by approximately 5% to 17%, depending on the nanostructure type added to the adhesive. Moreover, it was observed that there was an increase in loading of approximately 3% to 20% for the nanostructure reinforced joints obtained by using CFRCs with [0/90]6 stacking sequence.

Stress and Failure Analysis of Composite Prosthetic Leg

Prosthesis is an artificial substitute for body parts such as limbs, eye, tooth, etc. Generally, the prosthesis is referred to as a fabricated substitute used to assist the damaged part of the body. The devices are made up of light materials like plastics, aluminium, and composites materials. The prosthetic technology is aimed to replicate the body part which is damaged irreversibly due to unfortunate incidents. The present work deals with creation of an optimized design for the prosthetic leg proposed by Saito et al. [2]. The material of prosthetic leg proposed here is made up of Carbon Fiber Reinforced Polymer (CFRP) composite laminate, having unidirectional and cross-ply stacking sequence, which is analyzed for static stress and failure loads. From the results, it is evident that, while a uni-directional laminate can withstand a failure load of 4910 N, a cross-ply laminate withstands 4282 N. Also, the individual ply versus stress is studied in this work.

Strength Weakening Effect of High Prestatically Loaded Marble Subjected to Low-Frequency Dynamic Disturbance under Point Load

The deep high prestatically loaded rock is often subjected to low-frequency dynamic disturbance and exhibits unusual strength characteristics, and thus, it is important to investigate the strength characteristics under the coupling effect of prestatic load and low-frequency dynamic disturbance loading conditions. In this study, a series of point load tests were conducted on the high prestatically loaded marble subjected to low-frequency disturbance by the MTS system, focusing on exploring the role of prestatic load level and low-frequency disturbance frequency in the process of rock strength change. Based on the average static failure load (Fmax) of samples under the static point loading, the high prestatic load levels (Fp) were selected as 70%, 80%, and 90% of Fmax, the corresponding low-frequency dynamic disturbance was loaded by sinusoidal waves with amplitudes of 60%, 40%, and 20% of Fmax, and the low-frequency dynamic disturbance frequencies (f) are 1, 2, 5, and 10 Hz. The change curve of the point load strength with the prestatic load level or the disturbance frequency was analyzed, which indicates that the point load strength under the coupled high prestatic load and low-frequency dynamic disturbance load was significantly lower than that under the pure static loading, presenting a significant point load strength weakening effect. Only when Fp or f reaches a certain level, the point load strength decreases significantly as f or Fp increases. Moreover, the point load strength weakening rate was proposed to characterize the degree of strength weakening. The comprehensive analysis demonstrates that Fp has a greater effect on the point load strength weakening effect than f, which is mainly reflected in the point load strength weakening level dominated by the Fp, and the weakening degree is affected by f.

Non-linear response and buckling of imperfect laminated composite plates under in-plane pulse forces

This study presents a semi-analytical solution of the non-linear dynamic response, shock spectrum, and dynamic buckling of an imperfect angle-ply laminated composite plate under various types of in-plane pulse forces. The laminated composite plate is modeled using a higher-order shear deformation theory and von-Kármán geometric nonlinearity. The non-linear governing partial differential equations (PDEs) of imperfect laminated composite plates are derived via Hamilton’s principle. Using Galerkin’s method, the non-linear PDEs are transformed into non-linear algebraic equations for the static stability problems and non-linear ordinary differential equations for the dynamic problem such as dynamic response, shock spectrum, and dynamic buckling. The buckling load of the plate is obtained through the associated eigenvalue problem. The static failure load of the composite plate is evaluated using the post-buckling analysis based on the Tsai-Wu failure criterion. The dynamic response and shock spectrum of the composite plate are determined via Newmark’s method. The dynamic failure load of the plate is evaluated using Newmark’s method based on the Tsai-Wu failure criterion. Dynamic buckling is to be characterized by dynamic load factor (DLF), which is represented as the ratio of the dynamic failure load to the static failure load. Based on the pulse/shock duration time, the pulse forces are divided into three loading regimes known as impulsive, dynamic, and quasi-static. The study revealed that the DLF values are > 1, < 1, and [Formula: see text]1 respectively for the case of impulsive, dynamic, and quasi-static loading regimes of pulse force. The influences of various types of in-plane pulse forces, amplitude and time duration of pulse forces, and amplitude of initial geometric imperfections on the non-linear dynamic response, shock spectrum, and dynamic buckling behavior of the laminated composite plate are addressed in detail. The results will help in the appropriate design of the laminated composite plate against dynamic buckling.

Nonlinear Response and Buckling of Imperfect Plates Under In-Plane Pulse Forces: A Semi-analytical Investigation

This study presents a semi-analytical solution of the nonlinear dynamic response, shock spectrum, and dynamic buckling of a simply supported imperfect plate under various types of in-plane pulse forces. Here, the plate is modelled based on higher-order shear deformation theory (HSDT) considering the von-Karman geometric nonlinearity. The governing nonlinear partial differential equations (NLPDEs) of the imperfect plates are developed via Hamilton’s principle. Using Galerkin’s method, the NLPDEs are converted into sets of nonlinear algebraic equations (NLAEs) for static stability problems and nonlinear ordinary differential equations (NLODEs) for dynamic problems. The critical buckling load of the plate is obtained through the associated eigenvalue problem. The static failure load of the plate is evaluated using nonlinear static stability analysis based on the yield stress failure criterion. The dynamic response and shock spectrum of the plates are plotted via Newmark’s method. The dynamic failure load of the plate is evaluated using Newmark’s method based on the yield stress failure criterion. Dynamic load factor (DLF) is the ratio of dynamic failure load to static failure load. Based on the pulse duration time, the pulse forces are divided into three categories known as impulsive, dynamic, and quasi-static. In the case of impulsive, dynamic, and quasi-static loading regimes, DLF > 1, DLF < 1, and DLF $$\approx$$ 1, respectively. The results obtained from the current works will help in the appropriate design of the imperfect plates against dynamic buckling.

Effects of CNT modified adhesives and silane chemical pre-treatment on CFRP/steel bond behaviour and durability

Carbon fibre reinforced polymers have shown an ability to provide increased strength and rehabilitation properties to steel. However, under extreme environmental conditions adhered CFRP/steel joints undergo detrimental reductions in strength and durability. This paper explores the use of silane chemical barriers and adhesive modifications to improve bond durability and retard environmental damage and restrict bond degradation. Carbon nano tube immersion in adhesives created increases in mechanical properties however the cost, time and dispersion difficulties prevented viable industrial applications. The study experimentally tested steel-CFRP double-lap specimens prepared with combinations of epoxy adhesives and silane pre-treatment. Samples experienced ongoing static service loading while submerged in 5% NaCl solutions of varying temperatures. After immersion for different durations, samples were fatigue loaded for a set number of cycles, after which, static failure loads were determined. Comparing tensile bond strengths quantified the impact that environmental conditioning, fatigue loading and retarding barriers have on the bond durability of CFRP to steel.

The influence of GNP and nano-silica additives on fatigue life and crack initiation phase of Al-GFRP bonded lap joints subjected to four-point bending

As bonded components of many industrial structures are inevitably under bending fatigue loads, it is essential to improve their mechanical behavior under these loads. This paper aims to investigate the influence of adding graphene and silica nano-particles to Araldite 2015 adhesive on the fatigue behavior of aluminum-to-composite bonded single lap joints (SLJs) by a novel fixture under four-point bending. Four adhesive groups were prepared: I) neat, II) nano silica-reinforced, III) nano graphene-reinforced (groups II and III include 0.5 wt%, 1.0 wt%, and 1.5 wt% contents), and IV) a mixture of these particles (0.5 wt% of each particle). Besides, all nano-reinforced groups were prepared with similar processing steps including magnetic stirring (30 min duration, speed of 180 rpm) followed by ultrasonic mixing (1 h duration) and vacuum oven drying. Tensile tests indicated that the tensile strength of the graphene-reinforced bulk specimens was greater than that of silica-reinforced ones for 0.5 wt% and 1 wt% of filler contents. Also, the average static failure load (ASFL) of the graphene-reinforced SLJs under four-point load was greater than that of silica-reinforced joints for 0.5 wt% and 1 wt%, and it was lower than that of the silica-reinforced specimens for 1.5 wt% of particle contents due to the presence of more agglomeration of nano graphene particles in the adhesive. Then, for maximum fatigue loads of 40%–70% of ASFL, and load ratios of R = 0.5, 0, and −1, load vs. life cycle curves were examined for all SLJ groups. The ASFL and fatigue life of group IV SLJs (mixture of 0.5 wt% of each particle) were improved compared to the joints reinforced by separate usage of each particle with 1 wt% content. Using backface strain measurements, the influence of adding nano-particles on retarding the crack initiation phase was discussed under different load conditions. Finally, optical microscope observations indicated that adding nano-particles changes the failure mode from adhesive to cohesive. The major reinforcing mechanisms encountered in this research were interpreted by scanning electron microscopy.

Evaluation on compressive properties of composite laminates with a hole reinforced by metal plate

The in-plane compressive properties of carbon fibre reinforced polymer (CFRP) laminate with a hole is investigated. In order to compare the mechanical behavior, square or round metal plate as the reinforcement is placed near the hole of composite laminate on one side asymmetrically. Quasi-static compression experiment and Speckle approach are applied to the CFRP laminates before and after aluminum alloy reinforcement. Stress concentration, strain-load relation, fiber breakage are analyzed based on experimental results. We found that the static buckling and failure load and elastic modulus of the reinforced composite laminates are larger than the unreinforced composite laminate. The compression experimental result is consistent with the digital speckle experimental result. It is also found that the reinforcement of round metal plate is close to that of square metal plate in terms of the ratio of increased failure load to increased weight. Arch beam of the unreinforced composite laminate with open hole formed when bearing compression loading is analyzed and compared to that of the aluminum alloy plate reinforced composite laminates with open hole.

Strain rate dependency on failure load and stress intensity factor of single lap steel joints bonded with epoxy adhesive reinforced with nano‐Al2O3 sphere and rod particles

AbstractThe failure load of single‐lap steel joints (subjected to compressive force) with epoxy/nano‐Al2O3 adhesives containing 0.5, 1.0, 1.5, and 2.0 wt% of sphere and rod nano‐Al2O3 was analyzed at quasi‐static loading. At optimum wt% (1.5 wt%) of nano‐Al2O3, the failure load of epoxy/nano‐Al2O3 adhesive was determined at high strain rates using Kolsky bar. Critical stress intensity factor of the adhesive layer at the corner of single‐lap joints was calculated from the experimentally obtained failure load. A substantial improvement in the failure load and critical stress intensity factor of epoxy/nano‐Al2O3 adhesives was achieved compared to the base adhesive at quasi‐static and high shear strain rates. Whereas, the failure load of epoxy/nano‐Al2O3 adhesives containing 1.5 wt% of sphere and rod nano‐Al2O3 at high shear strain rates were 3 to 5 times more than the static failure load of adhesives. The reinforcement of sphere nano‐Al2O3 in epoxy had better performance on failure load and critical stress intensity factor of joints compared to rod nano‐Al2O3 under the compressive mode of loading.

Biomechanical Performance of Charcot-Specific Implants

Over the past 2 decades, an increased number of diabetic Charcot neuroarthropathy reconstructions have been performed. Despite advances in implant technology, arthrodesis complication rates remain high. This study examined the biomechanical properties (4-point bending, cantilever bending, and thread pullout resistance) of intramedullary implants designed for midfoot reconstruction. Large implants included A1 (7.4 mm cannulated stainless steel beam), B1 (6.5 mm solid titanium bolt), and C1 (7.0 mm cannulated titanium beam). Smaller implants included A2 (5.4 mm cannulated stainless steel beam) and C2 (5.0 mm solid titanium bolt). Four-point bending testing compared flexural properties of the body of the implants. Cantilever-bending testing was performed with the maximum bending moment being applied off the main thread of the implant to assess the thread portion. Thread pullout strength was tested by fixing the implants to a Sawbone block on a platform, and the distal portion of the implant in a clamp connected to loading actuator. Implant A1 demonstrated higher stiffness, force to failure, and fatigue compared to implants B1 and C1 (p < .05). Pullout strength of implant A1 was higher than implant B1 (p < .05). Thread fatigue strength of implant A1 was higher than implant C1 (p < .05). Implant A2 demonstrated higher stiffness, force to failure, tip fatigue strength, and thread pullout strength compared to implant C2 (p < .05), while implant C2 demonstrated higher body fatigue failure than implant A2 (p < .05). Alteration of beam/bolt parameters influences the biomechanical performance of implants used in Charcot reconstruction. Greater stiffness resists deformation, providing improved stability. Greater static failure load and fatigue limit improves the implant's ability to withstand higher and repetitive loads before failing This study should stimulate further clinical research to determine if these biomechanical properties translate into reduced implant failure rates and improved clinical outcomes in patients with diabetic Charcot neuroarthropathy.

Static and Fatigue Characteristics of Pinned Metal-Composite Joints

Metal-composite joining methods currently rely almost exclusively on the adhesive bonding, the application of mechanical fasteners or a combination of the methods, the pros and cons of which are well known. In this article, a manufacturing-oriented solution for increasing the static and fatigue characteristics of metal composite bolted T-joints loaded in the out-of-plane direction by reinforcing the composite basement with a thin metal plate having die cut pins is proposed. Static load–displacement and fatigue life curves were obtained experimentally for different types of joints. The results obtained showed that, for a fiberglass/epoxy laminate, the solution proposed increased its static and fatigue failure loads by 64 and 50% respectively. It was also found that pinned adhesive joints were more effective than the conventional bolted ones at high-cycle loadings (the number of cycles exceeded 104).

An investigation on fatigue life evaluation and crack initiation of Al-GFRP bonded lap joints under four-point bending

In this paper, fatigue life and crack initiation of aluminum-GFRP bonded lap joints are investigated under four-point bending loading. For this purpose, a new fixture was designed and constructed. Fatigue loads vs. number of cycles to failure (L-N) were obtained so that the influence of various load ratios on L-N were examined. Furthuremore, the load amplitude vs. number of cycle curves were investigated. In addition, the load amplitude vs. mean load curve was obtained at 100,000 cycles. The effect of different maximum fatigue loads and load ratios were investigated on crack initiation life by implementing the backface strain (BFS) measurement and using an optical microscope. From the results, it can be inferred that the life of the crack initiation phase is nearly equal to that of half of the total life for a maximum load of 50% of the static failure load, whereas it is negligible for maximum fatigue loads higher than 60% of the static failure load. It was found that for a load ratio of R = −1, the crack initiation phase is negligible. Moreover, It was found that BFS plots were ended to the L-N curve, and this curve could be considered as a limit for BFS plots. Finally, a combined diagram including L-N curve, BFS, initiation, and rapid failure curves can be used to predict the remaining life of a joint which is loaded up to a certain number of cycles.

Experimental investigation on environmental degradation of automotive mixed-adhesive joints

In this paper, environmental strength degradation of 180 different adhesive single lap joints (SLJ), including mono-adhesive Araldite 2015, mono-adhesive Araldite AV138, and a mixed-adhesive of Araldite 2015 and Araldite AV138 subjected to moist conditions are experimentally studied. Four different moist conditions, i.e. dry, 75.3, 84.2 RH% and immersion in tap water, have been taken into consideration and the specimens are tested after exposing to these environments at room temperature for 0, 35, 80 and 270 days. The specimens have been tested in two different strain rate, i.e. 1 mm/min and 100 mm/min. The results reveal that although, in a dry environment, mixed-adhesive joints have higher failure loads in comparison to mono-adhesive SLJs, in a moist environment, they have the highest reduction in static failure load with regard to the mono-adhesive ones. Moreover, despite the finally brittle trend in failure load, mixed-adhesives manifest a behavior very similar to ductile mono-adhesives regarding elongation. Analytical predictions of failure load are also consistent with the experimental observations in dry condition.