Cyclic Bending Loads Research Articles

Improving the fatigue behavior of dental implants through processing commercial purity titanium by equal-channel angular pressing

An investigation was conducted to evaluate the feasibility of using commercial purity (CP) titanium of grade 1 for dental implants after processing by equal-channel angular pressing (ECAP). The material was processed by ECAP for 4 passes at room temperature. Dental implants were machined from the unprocessed material and the material processed by ECAP and their mechanical properties were evaluated in tensile and compression testing and in fatigue using the conditions specified in the ISO 14801 standard for dental implants. The results show processing by ECAP increases the yield stress and the ultimate tensile stress but reduces the strain hardening rate and hence the overall elongation to failure. Although processing by ECAP increases the fatigue life using cyclic bending loads, a comparison with published data suggests the fatigue behavior CP Ti of grade 1 is slightly less satisfactory than for commercial implants fabricated from higher grade titanium alloys.

Modeling trabecular bone adaptation to local bending load regulated by mechanosensing osteocytes

Cancellous bone has a complicated three-dimensional porous microstructure that consists of strut-like or plate-like trabeculae. The arrangement of the trabeculae is remodeled throughout the organism’s lifetime to functionally adapt to the surrounding mechanical environment. During bone remodeling, osteocytes buried in the bone matrix are believed to play a pivotal role as mechanosensory cells and help regulate the coupling of osteoclastic bone resorption and osteoblastic bone formation according to the mechanical stimuli. Previously, we constructed a mathematical model of trabecular bone remodeling incorporating cellular mechanosensing and intercellular signal transmission, in which osteocytes are assumed to sense the flow of interstitial fluid as a mechanical stimulus that regulates bone remodeling. Our remodeling simulation could describe the reorientation of a single strut-like trabecula under uniaxial loading. In the present study, to investigate the effects of a bending load on trabecular bone remodeling, we simulated the morphological change in a single trabecula under a cyclic bending load based on our mathematical model. The simulation results showed that the application of the bending load influences not only the formation of the plate-like trabecula but also the changes in trabecular topology. These results suggest the possibility that the characteristic trabecular morphology, such as the strut-like or plate-like form, is determined depending on the local mechanical environment.

Seismic performance of circular RC bridge columns with flexure–torsion interaction

Reinforced concrete (RC) bridge columns for skewed, curved bridges and other kinds of irregular bridges can be subjected to combined loadings with axial load, shear force, flexure and torsion under multi-dimensional earthquake excitations. Combined loadings including torsion probably affect the seismic performance of these bridge columns. The experimental investigation on the seismic performance of circular RC bridge columns under combined cyclic bending and torsional loading is conducted in this paper. Twelve circular RC bridge column specimens are tested under various loading conditions: cyclic bending, cyclic torsion, and combined cyclic torsion and cyclic bending. Several combinations of cyclic bending and cyclic torsion are applied to evaluate the interaction between torsion and flexural capacity of bridge columns. The experimental results showed that the flexural capacity decreases and the damage tends to occur upward outside the flexural plastic hinge region as the level of applied cyclic torsion increases, and the torsional capacity decreases as the level of applied cyclic bending increases. The failure mode and deformation characteristics of RC bridge columns will be changed due to the effect of combined flexural and torsional loadings. The locking and unlocking effect of the spiral reinforcement on torsional and flexural envelopes of columns under pure torsion and combined cyclic bending and torsion is found. The influence of aspect ratio, longitudinal reinforcement ratio and type of spiral reinforcement on the seismic performance of columns under combined action with the same rotation-drift ratio is also discussed. An empirical flexural and torsional hysteretic model for circular RC columns with single spiral stirrup under combined cyclic bending and torsion is proposed based on the experimental results.

Fatigue behaviors of four-step three-dimensional braided composite material: a meso-scale approach computation

This paper reports the computational results of the bending fatigue behaviors of four-step three-dimensional rectangular braided composite materials from a meso-scale approach. A full-size meso-scale model of a four-step three-dimensional braided composite was established to numerically analyze the deformation and damage under cyclic bending loading. The stress distribution, energy absorption, hysteresis loop features and damage morphologies were obtained to explain the structural effects on the deformation and damage of the three-dimensional braided composite material subjected to three-point bending cyclic loading. The influences of the microstructure on the fatigue behaviors have been discussed for designing the three-dimensional braided composite material with high fatigue damage tolerance.

Experimental study of SS316L cantilevered cylindrical shells under cyclic bending load

In this research, softening and ratcheting behaviors of SS316L cantilevered cylindrical shells under cyclic bending load were investigated. Experimental tests were carried out by a Servo-Hydraulic INSTRON 8802 machine. Force-control and displacement-control loadings were applied and the effects of displacement amplitude, mean force, loading history and cutout position were examined. Under displacement-control loading, softening behavior was observed due to growth of ovalization and it was shown that as the displacement amplitude increases, softening rate and density of plastic energy increase. Accumulation of the plastic strain or ratcheting phenomenon occurred under force-control loading with nonzero mean force. Increase of the mean force accompanied with an increase in the accumulation of the plastic deformation and its rate. In loading history, it was seen that prior load with higher force amplitude retards the ratcheting behavior and plastic deformation of subsequent load with smaller force amplitude. In addition, due to sensitivity of cutout to the bending moment, as the position of the cutout changes from the middle of shell towards the cantilevered end, the accumulation of the plastic deformation increases.

Mechanical Response of Partially Prestressed Precast Concrete I-Beams after High-Range Cyclic Loading

The variations of three residual mechanical parameters in a set of partially prestressed, precast concrete I-beams after being subjected to concentrated high-level cyclic loading are presented and discussed. These three mechanical parameters are flexural stiffness, natural frequency, and crack width. Two precast prestressed I-beams were tested under three-point bending cyclic loads, varying between 60 and 90% of their ultimate moment. This range corresponds to 72 and 108% of cracking moment. Having reached a prefixed number of cycles, the cyclic load testing stopped, and static testing was done up to 90% of the ultimate moment. Variations of the three aforementioned mechanical parameters with the number of cycles were observed, especially the crack width. The main conclusion, in this case, is that cyclic loading caused insignificant variations in beam stiffness and, as a consequence, insignificant variations in the mechanical parameters. On the contrary, significant variations in crack widths were observed.

Research on Ultimate Strength and Accumulated Plastic Deflection of Box Beam under Cyclic Loading

The aim of this paper is to study the ultimate strength of a thin-wall box beam under cyclic bending loads. The nonlinear numerical simulations have been performed on the cyclic behaviors of a thin-walled box beam to investigate the ultimate strength and accumulative plastic deflection effect. Four cyclic loading cases are analyzed in the numerical simulations for the Fukumoto B-60-1 box beam model. The results of the simulations by the paper are discussed and they shall provide some valuable information to further study on the problem.

Fatigue Damage in Diameter-enlargement Part Formed by Cyclic Bending and Axial Compressive Load

We proposed a new cold processing method to partially enlarge the diameter of a shaft with a combination of a cyclic bending load and an axial compressive load that is lower than the yield stress of sample material. We call this cold processing method a diameter-enlargement working method, and call this processed part a diameter-enlargement part. Key features of the processing method are chiefly as follows: the diameter enlargement deformation progresses easily under a low axial compressive load at room temperature; the processed part has little temperature increase, although the processing causes large plastic deformation. We have tested the influence of the processing conditions and the mechanical properties of the sample materials in terms of diameter enlargement deformation behavior. However, little is known about the fatigue damage condition in a diameter- enlargement part. Therefore, we carried out processing experiments to clarify crack generation conditions, and simulated working processing using finite element method in order to investigate behaviors of stress and strain during the processing. Furthermore, we evaluated low cycle fatigue damage in the processed part by using the Manson-Coffin expression. This paper clarified the mechanism of crack generation during the processing and evaluates the fatigue strength of the processed part.

Finite Element Analysis of Concrete Filled Double-Skin (CHS Inner and CHS Outer) Steel Tubes under Lateral Impact

As a new type of steel-concrete composite structure, Concrete-Filled Double Skin Steel Tubes not only have the advantages of the traditional steel concrete structures, but also carried out cross-section and great bending stiffness. This structure is widely used in high-rise buildings, bridges and power facilities. During the whole life cycle, concrete-filled double skin steel tubes may inevitably suffer from various impact loads. In current the research about steel-concrete composite structure focuses on the performance about axial compression, bias, bending, and low cyclic loads. but the research about it under lateral impact is equally import. In this paper, the behavior of concrete-filled double skin steel tubes (CFDST) with fixed boundary condition was analyzed by Finite Element Analysis method ,to analyze the destruction modal, impact force (F) , deflection () as well as other dynamic responses of CFDST under different lateral impact energy. The work mechanic and full range analysis of concrete filled double steel tube under lateral impact were analyzed. The results show that the damage of CFDST with fixed boundary condition under lateral impact is in ductile manner. Analyzed the whole process of the dynamic response basically , laid the foundation for further parametric analysis and practical calculation method.

Finite element analyses of stress distributions of three-dimensional angle-interlock woven composite subjected to three-point bending cyclic loading

This paper presents the finite element simulation of stress distribution features of 3D layer-to-layer angle-interlock woven composite undergoing three-point bending cyclic loading. With the finite element analysis model, a microstructure shell element model of the woven composite at yarn level was established to calculate the fatigue behaviors and stress distribution during cyclic loading. The stress distributions in the warp, weft yarns, and the resin regions have been calculated to show the stress difference in the woven composite. It has been observed that the warp yarns share the most part of the stress or loading, i.e. the strength warp yarn is more important than that of the weft yarn for the fatigue design. In addition, the stress distributions at the locations where the weft yarns crossover the warp yarns have been investigated. The stress degradations of the top and bottom surface of the woven composite panels were also compared with those in experimental and good agreement was found. With the stress distribution in the woven composite, the method of improving the fatigue damage tolerance was expected to be developed.

Residual Compressive Stresses and Defects of Layers Hardened by Chemical Heat Treatment

Reasons for the occurrence of defects in hardened layers created by chemical heat treatment, and their effect on component operating efficiency under bending cyclic loading conditions are analyzed fundamentally. Specific examples are provided for the effect of residual stresses on actual component quality.

Structural effects of three-dimensional angle-interlock woven composite undergoing bending cyclic loading

This paper reports the structural effects of three-dimensional (3-D) angle-interlock woven composite (3DAWC) undergoing three-point bending cyclic loading from experimental and finite element analysis (FEA) approaches. In experiment, the fatigue tests were conducted to measure the bending deflection and to observe the damage morphologies. By the FEA approach, a micro-structural unit-cell model of the 3DAWC was established at the yarn level to simulate the fatigue damage. The stress degradation at the loading condition of constant deformation amplitude was calculated to show the degradation of mechanical properties. In addition, the stress distribution, fatigue damage evolution and critical damage regions were also obtained to qualitatively reveal the structural effects and damage mechanisms of the 3DAWC subjected to three-point bending cyclic loading.

Mechanisms of Failure of Locked-Plate Fixation of the Proximal Humerus

Locking plates are the predominant implants used for proximal humerus fractures. Despite a preponderance of good clinical outcomes, failures continue to occur. The purpose of this study was to investigate the failure mechanism of locked proximal humeral plate fixation and its relationship with bone density and screw length. Human cadaveric humeri were subjected to cyclic bending loads after an unstable 2-part fracture (Orthopedic Trauma Association classification 11 A-3) was created and stabilized with a locking proximal humeral plate. Acoustic emission (AE) sensors were mounted on the specimens to detect fracture displacement and generation of microcracks. The data were analyzed to evaluate construct failure. Eight of 10 locking plate constructs in cadaver specimens failed in varus collapse. The primary influences on failure were cancellous bone density and cancellous bone screw length. AE monitoring demonstrated patterns of microcrack progression, predominantly along the inferior screws. The progression trends according to AE were similar to their respective actuator displacement versus time curves. Cancellous bone density and total cancellous screw depth penetration seem to be critical variables. Although the patients' bone density cannot be controlled, surgeons may decrease the risk of failure by maximizing the length of the screws within the cancellous bone. Analysis of microcrack formation revealed that failures begin at the midportion and tips of the inferior screws and at the bone-plate interface of the inferior screws.

Effect of stress distribution on the tool joint failure of internal and external upset drill pipes

Detailed investigation was carried out on the tool joint failure of the internal & external upset (IEU) GSS105 drill pipes. Stresses were analyzed using 2D finite element method (FEM) for the threaded tool joint of the drill pipe under the combined loading conditions containing preload, tensile and bending loads. The stress concentration factors in the pin and box were calculated. Results showed that the maximum stress concentration occurred at the roots of the first tooth from the pin tool joint shoulder of the drill pipe. Fractographic observation revealed that the tool joint failure of the drill pipe was caused by fatigue crack nucleated at the tooth root and propagated through the wall of the tool joint. The deterioration of the fatigue resistance of the tool joint is related to dogleg region where severe cyclic bending load exists due to the local deviation of the drill pipe from the vertical line.

Numerical stress intensity factor calculation in flawed round bars validated by crack propagation tests

In this paper the results of crack propagation tests on round bars under cyclic tension and bending loading are presented. The tests were performed to investigate the crack geometry and its dependencies e.g. on the stress ratio and overloads. Furthermore, the crack propagation tests were used to validate the numerical stress intensity factor (SIF) calculation. This validation is necessary, due to the uncertainties in the numerical calculation of three-dimensional crack problems. As shown in literature, the 1/r-singularity of the stress field is not fulfilled in general for surface cracks in the near surface domain. Due to this boundary layer effect, the classical SIF is not valid. In order to calculate SIFs at the surface point an extrapolation is used. The method’s parameters are validated by the crack propagation tests and ensured by numerical investigations concerning the singularity of the stress field and the boundary layer thickness. These investigations were performed on a CT-specimen with a straight crack front.

Ratcheting failure of pressurised straight pipes and elbows under reversed bending

Ratcheting studies were carried out on Type 304LN stainless steel straight pipes and elbows subjected to steady internal pressure and cyclic bending load. The internal pressure for all the straight pipes was 35 MPa and in the case of elbows the internal pressure was varied for different elbows, ranging from 27.6 MPa to 39.2 MPa. Cyclic bending load was applied on the specimens by subjecting them to different levels of load-line displacement. The specimens have undergone significant ratchet swelling (ballooning), ovalization and consequent thinning of the cross-section during ratcheting. The straight pipes failed either by occurrence of through-wall crack accompanied by simultaneous ballooning, or bursting with simultaneous ballooning. All the elbows failed by occurrence of through-wall crack accompanied by simultaneous ballooning. Ratcheting behaviour of straight pipes and elbows were compared and it was generally inferred that ratcheting was more pronounced in straight pipes than in elbows.

Assessment of the Damageability of Low-Carbon Steel Welded Joint Zones under Cyclic Loading Conditions

The paper discusses the results of an experimental study of scattered-damage accumulation in butt-welded joints in St.3sp steel, which is widely used in the assembly of constructions in industry and civil engineering. Welded joints were subjected to inhomogeneous stresses under cyclic bending loading conditions. The degree of metal damage is assessed by the LM-hardness method. A linear correlation between metal damage coefficient and the value of operating bending stresses has been established.

Fatigue strength assessment of laser stake‐welded web‐core steel sandwich panels

ABSTRACTThis paper investigates the fatigue strength assessment of web‐core steel sandwich panels. The production of these structures is made possible by laser stake welding. The investigation in this study considered two series of panels, one being an empty steel structure and the other filled with in situ polyurethane foam in order to increase the panel stiffness. Both series were tested under cyclic bending loading condition (R = 0) until one of the panel joints failed completely. A 3D panel bending response was analysed using finite element method. The J‐integral values at the panel joints were obtained by means of plane strain finite element analysis and by using displacements from 3D panel response. The influence of the weld geometry on the J‐integral value was investigated. It was found that the J‐integral value is similar in the cases of the average and critical geometry. The contact between the joint plates is possible in some cases, but its influence proved to be insignificant for the fatigue strength assessment. The study further shows that by using the average geometry, the J‐integral approach was able to identify the critical panel joints and present the fatigue strength results from both panel series in a narrow scatterband. The fatigue strength at two million cycles obtained for the panels within this study was in agreement with the laser stake welds and other steel joint types from previous studies. However, the slope of the panels fatigue resistance curve was found to be shallower than in the case of joints.

Fatigue life prediction of RC beams strengthened with prestressed CFRP under cyclic bending loads

The application of prestressed carbon reinforced polymer (prestressed CFRP) in reinforced concrete (RC) members can improve the mechanical properties of strengthened structures and strengthening efficiency. This paper proposed a semi-empirical prediction formula of fatigue lives of the RC beams strengthened with prestressed CFRP under bending loads. The formula is established based on the fatigue life prediction method of RC beams and fatigue experimental data of non-prestressed CFRP reinforced beams done before. Fatigue effect coefficient of the formula was confirmed by the fatigue experiments of the RC beams strengthened with prestressed carbon fiber laminate (prestressed CFL) under cyclic bending loads. Fatigue lives of the strengthened beams predicted using the formula agreed well with the experimental data.

Propagation Behavior of Main Crack in Reinforced Concrete Beams Strengthened with CFRP under Cyclic Bending Load

Fatigue behavior of reinforced concrete (RC) beam can be improved by externally bonded fiber reinforced polymer (FRP). However, propagation behavior of a crack on the RC beam will have serious effect on the fatigue life of the beam strengthened with FRP. In this paper, a finite element (FE) procedure was developed to analysis the stress intensity factor (SIF) of the main crack and an experimental study was conducted to investigate the propagation rate of the main crack of the RC beam strengthened with carbon fiber laminate (CFL) under cyclic bending load. The FE analysis results show that the SIF near the main crack tip increases at the beginning and then decreases with the fatigue crack propagation. When relative crack length α is equal to 0.3, the SIF is maximum. When α approaches 0.75, the SIF approaches zero. A total of 3 RC beams strengthened with CFL were tested. The experimental results show that it is possible to divide the process of the crack propagation into three distinct phases, including crack initiation and then quickly propagation, stable propagation and then rest and unstable propagation. A semi-empirical equation based on the Paris Law was developed to predict the crack propagation rate.