Cyclic Bending Loads Research Articles

Reliability testing of solder joints under combined cyclic thermal and bending load for automotive applications

The cost and time efficient reliability qualification process of solder joints in automotive electronic assemblies requires accelerated temperature cycling (ATC) testing. This work introduces a load-dependent reliability assessment method on board level for solder joints of multilayer ceramic capacitors (MLCC) under superimposed cyclic thermal and 3-point bending load. For this purpose, a testing setup is developed to enable statistical testing of solder connections under accelerated load scenarios. The condition of solder joints is monitored online by means of impedance measurement until failure.In this work, solder joint failure of a large amount of MLCC 1206 components is experimentally investigated, where the following lifetime influencing factors are studied: solder volume variation and MLCC 1206 components from different suppliers.The resulting lifetime of solder joints with volume variation reveals, that under the same loading conditions smaller solder joints show a significantly lower survival probability compared to solder joints with larger volumes. Furthermore, significant differences in solder joint lifetime between components from two different suppliers are observed.In order to derive a load-dependent failure criterion using impedance measurement data, finite element (FE) simulation is performed under consideration of test boundary conditions. In this way, printed circuit board (PCB) deformation is determined, taking into account both the thermally and mechanically induced strains. It is shown, that the relationship between calculated load-dependent PCB strain amplitudes and experimentally detected solder joint failures are described by a power law leading to component Woehler curves for different failure probabilities.

Interaction analysis of a notching and cyclic bending process

The economic and ecological efficient production of steel wire fibers for reinforcing concrete is essential for exploiting their potential to reduce the required amount of building material. An innovative production process bases on the process chain notch rolling and cyclic bending. A sheet metal is notched on both sides and subsequently bent under undulated motion for causing a cyclic bending load in the formed notches. Due to damage effects during the cyclic bending, cracks initiate. The damage procedure and crack growth is influenced by the previous notched sheet called wire strip and the characteristics of the bending process. To analyze these effects, an influence and interaction study of the notches on the cyclic bending process is aspired. Based on a two-staged experimental design, the notching parameters notch tip radius and web height, which correlate with the amount of strain hardening, as well as the bending parameter bending angle, for identifying the interdependency of both processes, are evaluated. For study execution, an experimental model test for applying a cyclic bending load on a notched specimen is introduced.

Mayo 2A Olecranon Kırık Tespitinde K-teli veya Kanüllü Vida ile Uygulanan Gergi Bantlama Metodunun Karşılaştırması: Biyomekanik Çalışma

Aim: The study aimed to compare the biomechanical stability and strength of the tension band wiring method used to treat mayo 2A olecranon fractures with Kirschner (K)-wire or cannulated screw configurations. Material and Methods: A total of 24 anatomical ulna models (Sawbones Model 1004, Pacific Research Laboratories, Vashon Island, WA) used in the study were divided into two equal groups of 12, tension band fixation with K-wire (Group 1) and tension band fixation with cannulated screw (Group 2), and groups were compared. The mechanical comparison was performed with a universal measuring machine (Shimadzu Autograph 50 kN; Shimadzu Corp). Results: Fixation methods comparison (K-wire/cannulated screw) were the main factors that determined the stability and the strength of the internal fixation. The median flexion strength of Group 1 was 107.92 (range, 94.22-121.72) N, and that of Group 2 was 109.67 (range, 105.07-113.86) N. The median varus strength of Group 1 was 100.02 (range, 83.24-102.18) N, and that of Group 2 was 76.32 (range, 68.44-78.43) N. Varus strength and stiffness were significantly higher in the K-wire group than in the cannulated screw group (both p values were <0.001). No significant differences were detected between the groups regarding flexion strength and stiffness (both p values were 0.999). Conclusion: Although no significant differences were detected between the two fixations in flexion bending cyclic loading, a significantly more stable fixation was achieved in tension banding applied with K-wire in varus bending cyclic loading. No reduction loss was detected during cyclic loading tests in either technique.

Bending fatigue life enhancement of NiTi alloy by pre-strain warm surface mechanical attrition treatment

Many structures like medical stents made of superelastic NiTi shape memory alloy (SMA) are subjected to cyclic bending loads and show a limited fatigue life due to crack nucleation and growth in the surface layers under local tensile stress. Here, we enhance the bending fatigue life of NiTi plates by pre-strain warm surface mechanical attrition treatment (pw-SMAT) where the austenite phase is directly subjected to severe plastic deformation and grain refinement without inducing phase transformation. Amorphous and grain size gradient (5–100 nm) microstructures, as well as a maximum compressive residual stress of 1093 MPa are produced in the surface layer of the NiTi plates via the pw-SMAT. The compressive residual stress notably reduces the surface tensile stress from bending. The grain size gradient layers with improved hardness and reduced hysteresis have high fatigue crack nucleation resistance, while the middle large-grained layers of the plates have high fatigue crack growth resistance. The combined effects of the gradient nanostructure and the compressive residual stress substantially increase the bending fatigue life of the NiTi plates from an original 103 cycles to over 1.3 × 104 cycles. The results open up a new route to improve the bending fatigue life of NiTi plates by heterogenous nanostructures.

Observation of the interaction between transverse cracking and fibre breaks in non-crimp fabric composites subjected to cyclic bending fatigue damage mechanism

This work presents observations of fatigue damage in a quasi-unidirectional polymer reinforced composite made from basalt fibre non-crimp fabric and epoxy. Through observations over large areas, the study provides quantitative observations of the damage caused by the cyclic bending loads, with focus on the damage in the tension-tension loaded region of the specimens. The observations reveals that the fatigue damage mechanism that governs the stiffness degradation of the composite occurs only in regions subjected to tensile stresses. Damage incurred from tensile loads are governed by local interactions between transverse and longitudinal fibre bundles. It is determined that cracks in transverse bundles interact with longitudinal bundles to cause breakage of fibres. These fibre breaks are found to be the main driver for stiffness degradation of the material. Similar accounts exists in the literature based on qualitative observations. The current study provides evidence, in the form of quantifiable observations, to further strengthen the argument for considering the damage mechanism as the main cause of stiffness degradation in quasi-unidirectional non-crimp fabric composites.

Fatigue damage assessment of metal sandwich panels under four-point bending cyclic loading conditions

This paper aims to investigate the effects on metal sandwich panels with different dimple core designs using four-point bending simulation under constant and variable amplitude loading. A core design with cavity and porosity in the body structure was found to reduce the panel structural integrity. This would lead to unstable bonding between the panels and initiate an early delamination process. Sandwich panels consisting of AR500 as the outer layer and magnesium alloy AZ31B as the core material were simulated using dimples of different diameters and depths; 5.0 / 2.5 mm, 6.0 / 3.0 mm, 7.0 / 3.5 mm and 8.0 / 4.0 mm, at a range of 50 % to 90 % of maximum strength, based on the lowest material strength for cyclic loading. The results indicate that the highest fatigue damage of 85 % occurred at the effective region of the dimple area, where force was applied to the panel. A hemispherical dimple core 6.0 mm in diameter and 3.0 mm in depth produced a reduction of failure at the effective zone of more than 85 % and the regression coefficient was over 0.89. This illustrates that a large dimple size was vulnerable to early delamination failure at the dimple region.

Ratcheting evaluation of pressurized straight pipe using Ahmadzadeh–Varvani hardening rule

This study evaluates the Ahmadzadeh–Varvani (A-V) hardening rule for the ratcheting behavior of pressurized straight pipe made of austenitic stainless steel Z2CND18.12N under bending loading and vertical displacement control, respectively. Based on the quasi-three point bending apparatus, the straight pipe specimen is placed in a nearly horizontal position, and the applied displacement to the specimen achieves cyclic bending. The displacement is called as vertical displacement in this study. Firstly, the A-V model is implemented into ABAQUS with the radial return scheme with sub-increments; and the consistent tangent modulus is derived for A-V model, and gives quadratic convergence for the solution. And then the numerical calculation is developed to simulate ratcheting behavior of pressurized straight pipe. The influences of internal pressure, cyclic bending loading or cyclic vertical displacement, loading history and control modes on ratcheting strain of straight pipe are studied, respectively. By comparison with the experimental data, it is found that the predicted results of A-V model are in good agreement with the experimental data of pressurized straight pipe.

Evaluating the effectiveness of combined hardening models to determine the behavior of a plate with a hole under combined loadings

Geometrical discontinuities in a material such as holes and notches on machine elements are called as critical regions due to the stress concentrations. They are the potential failure initiation locations Therefore, researchers put significant effort on the prediction of the material response in these discontinuities under repetitive loadings. 
 Cyclic plasticity is concerned with the nonlinear material response under cyclic loadings. In this study, numerical cyclic stress – strain response of a plate with a hole was evaluated under the combined loadings which are cyclic bending and tensile loadings. Oxygen Free High Thermal Conductivity (OFHC) Copper alloy was considered as material, and finite element simulations were performed in Marc software. A user defined material subroutine known as Hypela2 was utilized in order to define the material response. The plasticity model used in the present study comprises J2 plasticity along with combined isotropic – kinematic hardening model. Evolution of the backstress was introduced by Armstrong – Frederic type kinematic hardening model. The results were compared with the literature study, and it was seen that presented hardening model provides accurate results in small cyclic strain range.

Kinematic Hardening Model Comparison of Square Hollow Section Under Cyclic Bending

This study compares the different linearity of the kinematic hardening model of the Square Hollow Section (SHS) under cyclic bending loading. Four specimens of a simple support beam cyclically tested in previous research are listed as hot-rolled, hot-finished, and two cold-formed. Using the bilinear, multilinear, and Chaboche models, each specimen is modeled in kinematic hardening. The variables or node sets for each linearity model are estimated using tensile test data, and Chaboche variables are obtained using the least-square fitting method. Each linearity model for each specimen is built-in FEA using a shell model. The numerical model applied the same cyclic loading history as the previous test. The numerical analysis comparison concluded that Chaboche and the multilinear kinematic model generate the expected result fitted to test hysteresis of cold-formed one and cold-formed 2 SHS, but the bilinear models are not fitted. Moreover, all kinematic models are not fit for the hot-rolled and hot-finished SHS compared to the test hysteresis. So, for hot-rolled and hot-finished SHS, the combined hardening is suggested; there is a possibility it is because of the lower yield ratio that both sections have. Overall, during a cyclic bending analysis of cold-formed SHS, multilinear or Chaboche models are preferable if the data is limited.

Influence of Pulse-Pause Sequences on the Self-Heating Behavior in Continuous Carbon Fiber-Reinforced Composites under Ultrasonic Cyclic Three-Point Bending Loads.

Several studies have been conducted in the Very High Cycle Fatigue (VHCF) regime on Carbon Fiber Reinforced Polymers (CFRP) in search of their fatigue limit beyond their typical service life, which is itself in the order of 108 loading cycles. The ultrasonic fatigue test (UFT) method has been recently gaining attention for conducting fatigue experiments up to 109 loading cycles. This can be attributed to the reduction of testing time, as the testing facility operates at a cyclic frequency of 20 kHz. The fatigue loading in UFT is usually performed in a pulse–pause sequence to avoid specimen heating and undesirable thermal effects. For this study, the pulse–pause combination of the UFT methodology was explored and its influence on the self-heating behavior of the CFRP material was analyzed. This was realized by monitoring the temperature evolution in the CFRP specimens at different pulse–pause combinations and correlating it with their final damage morphologies. From the obtained results, it is concluded that the specimen heating phenomenon depends on several variables such as cyclic loading amplitude, the pulse–pause combination, and the damage state of the material. Finally, it is proposed that the test procedure, as well as the testing time, can be further optimized by designing the experiments based on the self-heating characteristic of the composite and the glass transition temperature (Tg) of the polymer matrix.

A new fretting fatigue loading method and its finite element simulation

Fretting damage is caused by small relative displacement between two bodies. It can result in loosening of fasteners or fatigue cracks. The traditional mode of fretting fatigue loading is to add a fixed normal load on the fretting pad and a corresponding fatigue load on the free end of the specimen. A new fretting fatigue loading method is proposed to simulate the actual working condition of spline coupling. A 3D finite element model is implemented to simulate the contact state in the process of bending fretting fatigue. The influence of cyclic bending load on the stress and strain of contact surface is studied. The new model is proved to be correct and effective.

Experimental Study on Self-Centering Performance of the SMA Fiber Reinforced ECC Composite Beam.

The combination of superelastic shape memory alloy fibers and ECC materials can form a new SMA fiber reinforced ECC composite material (SMAF-ECC) with good self-centering performance. In order to study the self-centering performance of the new composite material, 6 groups of pre-notch beam specimens were made for three-point bending cyclic loading tests, and the failure phenomenon, hysteresis curve, self-centering effect and influencing factors of the specimens were analyzed. The research results show that when the SMA fibers are effectively anchored in the ECC matrix, the SMA fibers can exert the superelastic properties to provide the ECC beams with recoverying force, and realize the crack self-closure and deflection self-recovery function for the beams, with the minimum residual crack width and deflection is only 0.9 mm and 1.3 mm respectively. Increasing fiber content can cause a small increase in the self-centering ability of the beams. However, only when the fiber diameter is appropriate, better self-centering effect can be achieved, but the difference caused by fiber diameter in the test was only 5%. SMA Fiber end forms have significant influence on self-centering performance. The knotted end beam can get a more than 70% self-centering ratio, while the straight end beams and bended end beams have no self-centering ability. The research results provide important reference for the research and application of this new self-centering materials and their structures.

Evaluation and comparison of control and heat treated L-shape furniture joints produced from Scotch pine and ash wood under static bending and cyclic fatigue bending loadings

This study investigated how the mechanical properties of L-shape joints produced from heat treated Scotch pine or ash wood behaved under cyclic fatigue loading and compared this with the mechanical properties of non-heat treated wood materials. Additionally, static bending performances of the L-shape of joints were investigated and compared to fatigue bending performance of same type of joints. Results indicated that increasing number of staple from 6 to 8 and density generally increased static bending of L-shape joints. Static bending resistance of L-shape joints produced from control Ash wood significantly higher than those of L-shape joints produced from heat treated Ash wood while no significant difference were observed between static bending resistance L-shape joints produced from control Scotch pine and L-shape joints produced from heat treated Scotch pine wood. The fatigue bending resistances of L-shape joints produced from heat treated samples generally passed and failed the same loading steps with those produced from control samples which means both L-shape joints could be used in same service area. L-shape joints under static and fatigue loadings mostly indicated staple leg shear mode. The one under fatigue loading was more than the one under static loading. Additionally, some joints under fatigue loading indicated staple rupture. The overall ratio of static bending loading to cyclic fatigue bending loading for L-shape joints was obtained as 2.85.

Flexural Performance of Concrete Beams Reinforced with Continuous FRP Bars and Discrete Steel Fibers under Cyclic Loads.

This research investigated the flexural behavior of high-strength concrete beams reinforced with continuous basalt fiber-reinforced polymer (BFRP) bars and discrete steel fibers. Five concrete beams with the dimensions of 150 × 300 × 2100 mm3 were constructed and tested to failure under four-point bending cyclic loading. The specimens consisted of four BFRP-reinforced concrete beams with various reinforcement ratios (ρf), namely, 0.56%, 0.77%, 1.15%, and 1.65%, and one conventional steel-reinforced concrete beam for comparison purposes. The cracking behavior, failure modes, load-deflection behavior, residual deformation, and stiffness degradation of the beams were studied. Additionally, a deformation-based approach was used to analyze the deformability of the beams. The results show that an increase in the ρf effectively restrained the crack widths, deflections, and residual deformation while also enhancing the flexural bearing capacity of the beams. In comparison to the first displacement cycle, the bearing capacity dropped by 10% on average in the third cycle. The stiffness exhibited a fast to slow degradation trend until failure. The residual stiffnesses were higher in beams with a higher ρf. The over-reinforced beams had superior deformability than the under-reinforced beams, according to the deformability factors.

Performance of hemp-FRCM-strengthened beam subjected to cyclic loads

Fabric-reinforced cementitious matrix (FRCM) composites are materials that are usually applied to strengthen existing structures. In this study, a hemp mesh coated with epoxy was manufactured and combined with a cementitious matrix to strengthen a concrete beam. This beam was subjected to bending cyclic loading tests and a nondestructive modal analysis test. The modal analysis was performed to determine the dynamic elastic properties of the beam under pre-cracking, post-cracking, and strengthened conditions. The beam stiffness increased following strengthening with hemp-FRCM. The results of the experimental cyclic loading test showed that the hemp-FRCM system improved the load-bearing capacity of the beam at the service limit state by 42%. Analytical and numerical models were adjusted and validated using the experimental results, and both proved to be effective calculation tools. The models accurately reproduced the behaviour of the FRCM-strengthened concrete beam if the strengthening connection could prevent sliding and mortar debonding failures.

The effect of different pin configurations on cyclic stability in pediatric proximal humerus fracture fixation: A Sawbones model study

BackgroundIn sawbones with proximal humerus fracture model, three different fixation configurations, Parallel-Straight K-wires, Cross-Straight K-wires and Palm-Tree Method, were biomechanically compared. MethodsA total of 36 anatomical pediatric humerus sawbones models were used. They were divided into three equal groups; parallel fixation with straight K-wires (Group PS), cross fixation with straight K-wires (Group CS), and Palm-Tree Method (Group PT). Models were tested in abduction and torsional at a speed of 0.5 mm/s and a 0–5 mm displacement range. Loading (N) and Stiffness (N/mm) data were calculated and compared statistically. ResultsGroup PS was significantly higher than the other two groups in abduction bending cyclic load values (P<0.001). It was also significantly higher in Group CS than in Group PT (P < 0.001). No significant differences were detected between the three different fixation groups’ cyclic torsional load values (p < 0.05). ConclusionThe parallel configuration with straight K-wires will provide a more stable fixation than the cross configuration with straight or Palm-Tree Method in pediatric proximal humeral sawbones fracture modeling.

Effect of Nano-Clay Particles and Heat Treating on Pure and Fretting Fatigue Properties of Piston Aluminum Alloy under Stress-Controlled Cyclic Bending Loading

Effect of Nano-Clay Particles and Heat Treating on Pure and Fretting Fatigue Properties of Piston Aluminum Alloy under Stress-Controlled Cyclic Bending Loading

On the interaction of axial and bending loads in the weld root fatigue strength assessment of load-carrying cruciform joints

Current design standards and recommendations incorporate the nominal stress system for assessing the fatigue strength capacity of load-carrying cruciform (LCX) joints with the fillet welds and failing from the weld root. Thus far, bending-loaded joints have not been addressed in these standards. The aim of the present study is to investigate the fatigue performance of LCX joints subjected to cyclic axial and bending loads. Firstly, fatigue test data sets of such joints subjected to axial loading and bending loads in the adjoined plate component are extracted from the literature, and statistical analyses are carried out to evaluate the fatigue strength capacity using the nominal weld stresses (NWSs). Secondly, experimental fatigue tests are carried out on LCX joints made of ultra-high-strength steel (UHSS) grade using constant amplitude loading and subjected to combined axial and bending load to study the load interaction effects on the fatigue strength capacity. The results showed that the FAT36 detail category for the weld root failures is applicable for bending-loaded joints when applying NWSs calculated on the basis of effective throat thickness of weld and assuming linear-elastic stress distribution over the joint section. The effective notch stress analyses showed unconservative results for the tested joints, when applying FAT225 design curve with the reference radius of rref = 1.0 mm.

Methodology to evaluate stress corrosion cracking in ethanol environments, applied to circumferential welds on API 5 L steel pipelines

This work presents an experimental methodology developed to perform fatigue crack growth (FCG) and slow strain rate (SSR) tests in ethanol environments aiming to evaluate stress corrosion cracking (SCC) susceptibility of circumferential welds on steel pipelines. FCG and SSR specimens were machined from a welded pipe and the notches were properly designed to promote crack propagation in the different regions of the weld. Tests were carried out keeping the crack-tip region fully immersed in an ethanol solution, which was fueled by a circulation system to ensure replenishment and aeration throughout the test. When applied to a welded API X70 steel pipe, this experimental methodology proved to be an efficient and simple method to achieve relevant and important informations on environmentally assisted crack growth and SCC susceptibility. The method developed here is inserted in the aspects as follows:•Perform tests in slow strain rate and cyclic bend loading in circulating ethanol, to promote the fracture in the different regions of a circumferential weld joint of a steel pipe.•Investigate sensitivity to stress corrosion cracking (SCC) of these different weld regions in ethanolic environment.•This method presents constructive details of a suitable apparatus which the experiments can be easily replicated.

Bending cyclic behavior and scatter-band analysis of aluminum alloys under beneficial and detrimental conditions through high-cycle fatigue regime

This article presents the bending fatigue behavior and the scatter-band analysis of aluminum alloys under beneficial conditions of nano-clay-particles and heat-treating, compared to detrimental conditions of the mechanical stress and the corrosion. Moreover, the sensitivity analysis was also done on the stress level, the pre-corrosion phenomenon, the addition of nano-particles and applying the heat treatment on the high-cycle bending fatigue lifetime of the aluminum-silicon alloy. For this objective, gravity and stir-casting processes were done for aluminum alloy and nano-clay-composite specimens and then, standard samples were machined from initial casted cylinders. Furthermore, rotary fatigue tests were performed under cyclic bending loadings, through the high-cycle fatigue regime. Some samples were pre-corroded in the sulfuric acid for 200 hours. Based on the sensitivity analysis on experimental data by the Minitab software, the obtained results indicated that the stress level was the effective parameter on the fatigue lifetime. The meaningful regression model was calculated and calibrated on the logarithmic scale of the fatigue lifetime. Then, the second sensitive parameter was demonstrated as the pre-corrosion, which caused a significant degradation of fatigue properties in the material. The last-ranked factor was related to nano-particles for the beneficial effect on the improvement of the high-cycle fatigue lifetime. The scatter-band analysis illustrated that nano-particles and heat-treating changed the scattering behavior of experimental data.