Cyclic Bending Loads Research Articles

Ratcheting Strain Assessment in Pressurised Stainless Steel Elbows Subjected to In-plane Bending

Abstract Ratcheting studies were carried out on Type 304LN stainless steel elbows, by applying steady internal pressure and cyclic bending. The elbows were of 168 mm nominal outer diameter and the average thickness varied from 14.7 mm to 15.1 mm. The elbows filled with water were pressurized between 27.6 MPa and 39.2 MPa. Cyclic bending load, under the opening and closing moments, was applied on the elbows at ambient temperature. During the ratcheting experiments, strains were measured at different locations in the curved and straight portions of the elbows using post-yield rosette strain gauges. Ratcheting strain and its rate of change were estimated at different locations of the elbows with increase in number of cycles. In the curved portion of the elbow, ratcheting strain was observed in the hoop direction at the intrados, crown and at a few other locations other than the extrados. No significant ratcheting was observed in both the axial and circumferential directions at the extrados location for all the specimens. The specimens failed by the occurrence of through-wall axial crack in the curved portion, at one of the crown locations, accompanied by simultaneous bulging.

Influence of plasma and cold spray deposited Ti Layers on high-cycle fatigue properties of Ti6Al4V substrates

This paper presents a summary of the research on the influence of plasma and cold spray deposition of bio-grade Ti powder on the high-cycle fatigue properties of Ti6Al4V substrates.Four sets of flat specimens (as-received, grit-blasted, plasma and cold sprayed) were prepared and subjected to cantilever–beam cyclic bend loading with a constant deflection of the free end.It was found that the grit-blasting procedure significantly increased the fatigue lives of the specimens compared to the as-received set (1.81× increase). The deposition of the coatings onto grit-blasted specimens led to deterioration of fatigue properties. The average fatigue lives of the plasma sprayed and cold sprayed samples reached 1.16× and 0.91× of the as-received specimens, respectively.In order to understand the positive effect of the grit-blasting procedure and the adverse effect of the coatings deposition on fatigue lives, chemical analyses, fractographic analysis, microstructural investigations as well as layers elastic moduli estimation were carried out. It was found that the cold spray deposition retained the composition of the powder feedstock while a complete transformation of Ti into nitrides and oxides was detected in the plasma deposited layers. Owing to the different coating build-up principles and their respective different porosity levels, the moduli of the coatings were found to vary (7.2GPa for plasma sprayed and 36.7GPa for cold sprayed layers). The fatigue crack initiation sites and propagation directions in the plasma and cold sprayed specimens were found to differ substantially. Based on the obtained results, two explanations of the fatigue loading results are suggested in the paper.

Fatigue Strength of Shaft with Diameter Enlarged Partially by Cyclic Bending and Axial Compressive Loading

This paper experimentally and analytically investigates the fatigue strength and of mechanical damage of the processed shafts. First, we carry out rotary bending fatigue tests and investigate the fatigue strength for smooth specimens, specimen made only using cutting work, and specimens processed using a new plastic working developed originally. Secondly, we measure the Vickers hardness values to investigate strain hardening near the processed part. Finally, we simulate stress and strain distributions of the shaft during the processing using finite element method (FEM) and calculate the stress concentration rate at the notch root of the processed part. Based on the processing experiments and the finite element analyses (FEA), we clarify that the plastic work mechanically does not reduce the fatigue strength of shafts in the processing range.

Fatigue behavior of recycled aggregate concrete under compression and bending cyclic loadings

The fatigue behavior of recycled aggregate concrete (RAC) with 100% recycled coarse aggregate (RCA) replacement percentage under uniaxial compression was experimentally investigated in this study. Key quantities, including the residual strain variation, fatigue strain variation and the fatigue modulus of RAC, were calculated and analyzed to correlate the strain response and fatigue damage behavior of RAC. It is found that there exist no obvious differences of compressive fatigue behavior between RAC and natural aggregate concrete (NAC). Based on the experimental results and continuum damage mechanics, a fatigue model relating the fatigue strain variation and the fatigue modulus degradation to the fatigue damage evolution is proposed. Furthermore, RAC with 100% RCA replacement percentage was also tested under cyclic bend loading. It is found that the fatigue life of RAC is lower than that of NAC for the same stress level under cyclic bend loading.

반복굽힘 조건에서 감육 곡관의 피로손상 거동

본 연구에서는 감육결함이 가공된 실배관 곡관 시편을 대상으로 10 MPa의 내압과 반복 굽힘하중 조건에서 피로 시험을 수행하였다. 시험에는 감육결함이 곡관의 외호부와 내호부에 존재하는 경우를 고려하였으며, 반복 하중으로는 완전 역방향의 변위제어 형태로 작용되는 In-plane 상의 굽힘하중이 고려되었다. 실험 결과, 감육결함이 곡관의 외호부에 존재하는 경우에는 결함부가 아닌 곡관의 측면에서 축방향 균열이 생성되었다. 또한, ASME Sec.Ⅲ의 설계 피로곡선에서 예측된 건전 곡관의 피로수명보다 긴 피로수명을 보였으며, 피로수명이 결함 길이에 크게 영향을 받지 않았다. 반면, 결함이 내호부에 존재하는 곡관은 내호부에서 원주방향 균열이 발생하였으며, 피로수명은 ASME Sec.Ⅲ의 설계 피로곡선에서 예측한 건전 곡관의 피로수명보다 짧은 값을 보였다. 또한, 내호부 감육 곡관의 피로수명은 결함 길이가 감소함에 따라 뚜렷이 감소하였다.<BR>

Ratcheting Studies on Type 304LN Stainless Steel Elbows subjected to Combined Internal Pressure and In-Plane Bending Moment

Abstract “Ratcheting” is a phenomenon which leads to reduction in fatigue life of a structural component by loss of ductility due to cycle by cycle accumulation of plastic strain. Ratcheting occurs in a structure subjected to a combination of steady/sustained and cyclic loads such that the material response is in inelastic region. Ratcheting studies were carried out on Type 304LN stainless steel elbows, subjected to steady internal pressure and cyclic bending. The elbows filled with water were pressurized between 27.6 MPa and 39.2 MPa. Cyclic bending load, under opening and closing moments, was applied on the elbows at ambient temperature. Number of cycles corresponding to occurrence of a through-wall crack was recorded. Crack was observed in the bent portion at one of the crown locations in all the four specimens. Maximum strain was observed at the intrados and crown locations of the elbows. The ratcheting strain increased with number of cycles at crown and intrados locations. However, the strain accumulation rate decreased with number of cycles. Strain was observed to be minimum at the extrados location and the same stabilized toward the end of the tests. The specimens have failed by occurrence of through-wall axial crack accompanied by simultaneous ballooning. The ballooning was found to be varying from 3.8% to 5.8% with respect to the original circumference in the bent portion. The reduction in thickness was found to be around 12%–15%.

Comparisons of static bending and fatigue damage between 3D angle-interlock and 3D orthogonal woven composites

This paper presents the comparisons of quasi-static three-point bending and fatigue damage behaviors between the three-dimensional angle-interlock woven composite and the three-dimensional orthogonal woven composite. The stress–deflection curves and failure modes were recorded to compare both composites’ mechanical properties under quasi-static bending loading condition. The S-N curves were obtained to demonstrate the comparison of fatigue life under various stress levels between three-dimensional angle-interlock woven composite and three-dimensional orthogonal woven composite. In addition, the damage indexes versus number of cycles (D-N) curves were given to characterize the three-stage cumulative fatigue damage evolution of both types of textile structural composites. Furthermore, the ultimate damage morphologies were compared to deduce the structural effects of the composites under three-point bending cyclic loading condition.

Cumulative fatigue damage for 3-D angle-interlock woven composite under three-point bending cyclic loading

This article presents the quantitative characterization of cumulative fatigue damage behavior for the three-dimensional angle-interlock woven composite undergoing three-point bending cyclic loading. The S–N curve was obtained to demonstrate the fatigue life of the three-dimensional angle-interlock woven composite under different stress levels. The increment of cycles for each 5% interval of stress level was reported to show the difference of fatigue resistance performances of the three-dimensional angle-interlock woven composite among the high, middle, and low intervals of stress level. In addition, the Cumulative Fatigue Damage versus Number of Cycles (D–N) curve and the Deflection Index versus Number of Cycles (F–N) curve were deduced to characterize the three-stage cumulative fatigue damage. Furthermore, the damage morphologies of the three-dimensional angle-interlock woven composite after fatigue tests were photographed to compare with those in quasi-static test. The cracks initiation and propagation in the three-dimensional angle-interlock woven composite during the process of cyclic loading were summarized to find the mechanisms of fatigue damage development.

A biomechanical study comparing plate fixation using unicortical and bicortical screws in transverse metacarpal fracture models subjected to cyclic loading

The use of bicortical screws to fix metacarpal fractures has been suggested to provide no added biomechanical advantage over unicortical screw fixation. However, this was only demonstrated in static loading regimes, which may not be representative of biological conditions. The present study was done to determine whether similar outcomes are obtained when cyclic loading is applied. Transverse midshaft osteotomies were created in 20 metacarpals harvested from three cadavers. Fractures were stabilised using 2.0 mm mini fragment plates fixed with either bicortical or unicortical screw fixation. These fixations were tested to failure with a three-point bending cyclic loading protocol using an electromechanical microtester and a 1 kN load cell. The mean load to failure was 370 N (SD 116) for unicortical fixation and 450 N (SD 135) for bicortical fixation. Significant differences between these two constructs were observed. A biomechanical advantage was found when using bicortical screws in metacarpal fracture plating.

Modeling Stress Responses of Multilayer Capacitors Using Varying Termination Geometries

Environmental regulations and increasingly challenging design objectives have prompted the search for alternative materials in microelectronics. Employing these materials alters the reliability profile and performance characteristics of the electronic components into which they are integrated. This article explores how mechanical stresses impact the reliability of ceramic dielectric bodies of multilayer ceramic capacitors (MLCCs) when the material, shape, and thickness of the MLCC terminations were varied. The termination material, termination geometry, and thickness of the ceramic were varied. Results were obtained using finite element analysis, and a reliability model was developed and validated. A preliminary investigation indicated a relationship between the selection of materials used for capacitor termination and the emergence of cracks. Stresses that occurred when boards were subjected to conditions including cyclic bending, vibrations, temperature cycling, and high-g loading correlated to the appearance of cracks on the bottom of the capacitor in proximity to the termination.

Cyclic Quasi-Static Testing of Hollow Structural Section Beam Members

AbstractThe efficient compression, torsion, and bending behavior of hollow structural sections (HSS) combined with their high strength-to-weight ratio provide an opportunity to further their use in seismic applications and improve on structural performance. However, current applications of HSS in seismic systems are restricted because of a limited understanding of their cyclic bending behavior. To characterize the behavior of HSS under pure bending and determine limiting values for their use up to large rotation levels, 11 different HSS beam members ranging in size from HSS 203.2×101.6×6.4 mm to HSS 304.8×152.4×6.4 mm with thickness of 6.4 and 9.5 mm are tested under cyclic bending loads. The moment-rotation results suggest that the width-thickness and depth-thickness ratios are important in determining whether a stable plastic hinge can be sustained during cycling, ensuring adequate ductility. Cycling effects associated with increasing rotation levels and multiple cycles at the same level are considere...

Soundness Diagnosis Of A Steel Bridge Pier Repaired By Heating/Pressing

In order to diagnose the soundness of a steel bridge pier, repaired by heating/pressing, a series of experiments and analyses were conducted. A virgin specimen was first locally buckled by cyclic bending loads and subsequently corrected by heating/pressing. The corrected specimen was again subjected to the same loading experiment as the virgin specimen. In addition, loading experiments were simulated by elastic-plastic large deformation analysis. It was confirmed that heating temperatures should be kept below the A1 transformation temperature (around 700 °C within the general structural steel) to prevent changes to its mechanical properties. It was ideal for the imperfection, which was the residual deformation in the panel, to be controlled within the acceptance of the initial deflection. Further, it was found that correcting the residual deformation opposite the mode of local buckling of the panel was an effective method for maintaining the maximum strength of the repaired pier, equivalent to that of the virgin specimen.

Study of the short and long fatigue cracks for brass alloy

In this study the effect of short and long cracks for brass alloys specimens exposed to bending cyclic load is investigated, this test applied on a group of standard specimens until its fracture, data taken could be drawn as a curve between stress and number of cycles (S-N) curves which gives the fatigue limit. Results obtained theoretically and experimentally, that are concluded decreasing in the applied load cause increasing the age and applying high loads in the beginning and at the end given almost smaller number specimen age and the quick growth of short cracks followed by quick growth of long cracks, that the values taken from the theoretical equations are always greater than experimental number of cycles of failure. Key words: Fatigue, varying loads, short cracks, long cracks, brass alloy.

Fatigue lives of RC beams strengthened with CFRP at different temperatures under cyclic bending loads

ABSTRACTFatigue performance of reinforced concrete (RC) components strengthened with fibre reinforced polymer (FRP) is largely improved. However, temperature changes of service environment have a great effect on the fatigue behaviour of RC components strengthened with FRP. Concerning about temperature variations in subtropical areas such as South China, this paper analyses the fatigue behaviour of RC beams strengthened with carbon fibre laminate (CFL) from experimental studies and theoretical analysis under four different temperatures (5 °C, 20 °C, 50 °C, 80 °C) and five different stress levels (0.60, 0.66, 0.72, 0.78, 0.84). The paper discusses temperature fatigue behaviour of RC beams strengthened with CFL under cyclic bending loads in different service environments, and proposes a calculation formula of fatigue lives of RC beams strengthened with CFL under environmental temperatures and external forces coupling. Experimental results show that the formula not only effectively predicts the fatigue lives of the RC beams strengthened with CFL under environmental temperatures and bending loads coupling but also estimates the fatigue limits.

Biomechanical Comparison of Fixation Techniques in Midshaft Clavicular Fractures

The purpose of this study is to evaluate the biomechanical properties and the stability among a locking clavicle plate (LCP), a dynamic compression plate (DCP) and an external fixator (Ex-fix) in an unstable displaced clavicle fracture model under torsional and three-point bending loading. Forty-eight human adult formalin-fixed clavicles were paired according to their bone mineral density homogeneously into three groups: LCP, DCP, and Ex-fix. Each specimen was osteotomized at the midshaft. Torsional and three-point bending forces were performed for 1000 cycles with stiffness recorded at 10 cycles (initial) and then at 100-cycle intervals thereafter. Initial stiffness, failure loads, and the percentage of initial stiffness at the various intervals were compared using analysis of variance. The mean initial stiffness values (Nmm/deg) for torsion were 703.2 (LCP), 448.1 (DCP), and 365.2 (Ex-fix). The mean failure moments (Nmm) for torsion were 7671.7 (LCP), 4370.3 (DCP), and 2999.7 (Ex-fix). The mean initial stiffness (Nmm) for bending were 32.6 (LCP), 23.4 (DCP), and 20.6 (Ex-fix). The mean failure loads (N) for bending were 213.2 (LCP), 131.1 (DCP), and 102.7 (Ex-fix). For both torsion and bending, an overall significant difference among the three constructs in terms of failure loads and also a significant difference between the locking plate and the other two models only in terms of initial stiffness was seen. For torsion and bending, at all cyclic intervals, there was a significant difference between the locking plate and the other two models. After 700 cycles, a significant difference was also detected between the DCP and Ex-fix in torsion, but no difference was found between these groups at any cyclic interval in bending. The locking plate is significantly more stable than DCP and Ex-fix under torsional and bending cyclic loading in a displaced fracture clavicle model.

Shakedown and limit analysis of 90° pipe bends under internal pressure, cyclic in-plane bending and cyclic thermal loading

The Linear Matching Method is used to create the shakedown limit and limit load interaction curves of 90° pipe bends for a range of bend factors. Two load cases are considered i) internal pressure and in-plane bending (which includes opening, closing and reversed bending) and ii) internal pressure and a cyclic through wall temperature difference giving rise to thermal stresses. The effects of the ratios of bend radius to pipe mean radius ( R/ r) and mean radius to wall thickness ( r/ t) on the limit load and shakedown behaviour are presented.

Fatigue strength of the Cu/Si interface in nano-components

The fracture behavior of the Cu/Si interface in a nano-cantilever specimen with a 200 nm-thick Cu film (Specimen-200), which possesses a nanometer-scale strain-concentrated region, is examined under a cyclic bending load. The fatigue strength is around GPa level owing to the high yield stress of the Cu nano-film and the deformation constraint associated with the neighboring hard materials. The S– N curve shows clear dependence of fatigue life on the applied stress in the high-stress range, Δ σ. Specimens with a 20 nm-thick Cu film (Specimen-20) are also investigated for comparison. The stress range in the fatigue fracture of Specimen-20 is higher than that of Specimen-200 for the same fatigue life. However, there is good coincidence in the Δ σ/ σ s ( σ s: strength in monotonic load) vs. N f (number of cycles to fracture) at high Δ σ. The S– N curves suggest the existence of a fatigue threshold (Δ σ w) at low Δ σ. The ratio of fatigue limit to the fracture stress in a monotonic loading, Δ σ w/ σ s, is large compared with the magnitude of bulk metal, which suggests the brittle behavior of the interface. Moreover, the fatigue limits have good coincidence with their yield stresses.

Fatigue fracture expertise of train engine crankshafts

A failure investigation has been conducted on three cases of failed diesel engine crankshafts used in train and made up of forged carbon steel. The chemical composition and the mechanical properties of the crankshafts material including tensile properties, micro-hardness and toughness were evaluated. The crankshafts examination shows that all failures occurred after a fatigue process. The failure zones comprise the fractured surfaces observation, show the presence of beach marks with semi-elliptical shape surrounding the fracture origins indicate its progressive growth character. The cracks initiation can occur as a result of mechanical and thermal fatigue loads, due to the high stress concentration on fillet radius and the unusual friction between journals and bearings, respectively. Nevertheless, the cracks propagation was only attributed to the mechanical fatigue produced under cyclic bending and torsion loadings.

Experimental and probabilistic analysis of distal femoral periprosthetic fracture: a comparison of locking plate and intramedullary nail fixation. Part A: experimental investigation

The following is a two-part study. Part A evaluates biomechanically intramedullary (IM) nails vs. locking plates for fixation of femoral fractures in osteoporotic bone. Part B of this study introduces a deterministic finite element model of each construct type and investigates the probability of periprosthetic fracture of the locking plate compared with the retrograde IM nail using Monte Carlo simulation. For Part A, an extra-articular, metaphyseal wedge fracture pattern was created in 11 osteoporotic fourth-generation composite femurs. Fixation was performed with a locking plate or a retrograde IM nail. Axial, torsion and bending cyclic loading to simulate post-operative damage accumulation were performed followed by ramped load to failure. Locking plates proved to be more stable (using stiffness as the determining factor) in osteoporotic bone as observed under low load cycle conditions. However, some of these advantages were offset by a greater incidence of sudden periprosthetic fracture observed under ramped loading conditions. Cadaveric, osteoporotic femurs included as a case study also exhibited periprosthetic fracture, but failure was accompanied by catastrophic comminution of the cortex. Periprosthetic failure at the implant end including bone comminution is difficult to salvage with revision fixation. The weakened trabecular matrix and thinned cortex of osteoporotic bone may increase the incidence of periprosthetic fracture. It is, therefore, essential for the surgeon to consider all possible loading scenarios when recommending an ideal implant for the osteoporotic patient.

Crack Growth Prediction Method Considering Interaction between Multiple Cracks (Growth of Surface Cracks of Dissimilar Size under Cyclic Tensile and Bending Load)

When multiple cracks approach one another, the stress intensity factor is likely to change due to the interaction of the stress field. This causes change in growth rate and shape of cracks. In particular, when cracks are in parallel position to the loading direction, the shape of cracks becomes non-planar. In this study, the complex growth of interacting cracks is evaluated by using the S-Version finite element method, in which local detailed finite element mesh (local mesh) is superposed on coarse finite element model (global mesh) representing the global structure. In order to investigate the effect of interaction on the growth behavior, two parallel surface cracks are subjected to cyclic tensile or bending load. It is shown that the smaller crack is shielded by larger crack due to the interaction and stops growing when the difference in size of two cracks is significant. Based on simulations of various conditions, a procedure and criteria for evaluating crack growth for fitness-for-service assessment is proposed. According to the procedure, the interaction is not necessary to be considered in the crack growth prediction when the difference in size of two cracks exceeds the criterion.