Rotating Bending Moment Research Articles

Cyclic Loading on Damaged AA7075-T6 Specimens: Numerical Modelling and Experimental Testing

AA7075-T6 is widely used in the aviation and aerospace industries thanks to its interesting strength-to-weight ratio. The fatigue life of the structural components of aircrafts and rockets can be altered as a consequence of the impact of alien objects. This work investigates the fatigue behavior of an AA7075-T6 hourglass specimen induced by the impact of a steel ball at its minimum cross-section. The specimen is then tested with a rotating bending moment. The stress distributions after impact and during cyclic loading are estimated using the Finite Element (FE) method. The failure mechanism was clarified by the observation of the failed specimen surface.

In Vitro Biomechanical Evaluation of a Novel, Minimally Invasive, Sacroiliac Joint Fixation Device.

Sacroiliac (SI) joint pathology may result in low-back pain, which causes substantial disability. Treatment failure with operative management of SI pain may be related to incomplete fusion of the joint and to fixation failure. The objective of this study was to evaluate the initial biomechanical stability of SI joint fixation with a novel implantable device in an in vitro human cadaveric model. The right and left sides of 3 cadaveric L4-pelvis specimens were tested (1) intact, (2) destabilized, and (3) instrumented with an implantable SI joint fixation device using a simulated single-stance load condition. Right-leg and left-leg stance data were grouped together for a sample size of 6, and angular range of motion (ROM) was determined during application of flexion-extension, lateral bending, and axial rotation bending moments to a limit of 7.5 Nm. Following intact testing, destabilization by severing the posterior SI joint capsule and ligaments and the pubic symphysis reliably produced a significantly destabilized joint with the mean angular ROM more than doubling in flexion-extension and lateral bending and more than tripling in axial rotation (P ≤ .003) compared to the intact condition. Instrumentation with the SI screw fixation device significantly reduced mean joint ROM compared to the destabilized condition in all 3 anatomic planes tested (P < .001). When compared to the intact condition, the SI-instrumented condition significantly reduced lateral bending (P = .01) and had a similar ROM in flexion-extension (P = .14) and axial rotation (P = .85). Instrumentation with the SI screw fixation device significantly reduced mean joint ROM compared to the destabilized condition, with similar ROM in flexion-extension and axial rotation, and it significantly reduced ROM in lateral bending compared to that for the intact joint. The ROM values observed with the instrumented condition were comparable to levels of mobility considered favorable for spinal fusion.

Dynamic aspects during full scale rotating bending axle tests using new generation of facilities with increased load frequency

According to EN 13261, EN 13103, EN 13104, rotating bending fatigue tests of full scale axles are one of the requested tests, when a new axle type, new material supplier or new manufacturer is intending to provide components for railway rolling stock. One of the test methods, how to generate the rotating bending moment, is to attach the half wheelset using the wheel to the horizontal ground base and to rotate an eccentric mass on the axle top. Such principle is used in the majority of test rigs available on the market. In the past, typical load frequency was 15 – 17 Hz. Under such conditions, only dynamic forces of the eccentric mass could be considered. However, recent design changes of the Sincotec facilities have resulted in increase of test frequencies to more than 25 – 30 Hz, which makes the tests significantly shorter. On the other hand, unlike the previous case, dynamic aspects of loading calibration have to be considered. A detailed example is shown and discussed. At static loading, the experimentally evaluated stresses on the axle surface corresponded to theoretical values exactly with the exception of near hub edge area, where an expected stress redistribution occurred. When the axle was loaded dynamically by rotating bending, the stress distribution on the axle surface was changed due to additional centrifugal forces of the axle itself, whereas at test frequencies around 30 Hz, such additional forces could no more be neglected. Note that the new character of load distribution cannot be always considered as optimum.

A multiaxial fretting fatigue test for spline coupling contact

ABSTRACTA novel fretting fatigue experimental methodology is presented for mimicking the salient fretting variables for arbitrary axial locations within a complex spline coupling geometry, under combined torque, axial loading and rotating bending moment. The approach permits the simulation, in a simplified test arrangement, of the superimposed multiaxial fretting conditions between the spline teeth. This is achieved via the combination of a low frequency in‐plane cyclic normal clamping load and a higher frequency out‐of‐plane cyclic fatigue stress. The latter is known from spline fatigue tests to play a critical role, along with torque and axial loads, in fretting fatigue cracking of splines.

Multiaxial fretting fatigue testing and prediction for splined couplings

This paper presents a combined experimental and computational methodology for fretting fatigue life prediction of aeroengine splined couplings under combined loading cycles involving cyclic torque and axial load, as well as rotating bending and fluctuating torque. The experimental method is based on the concept of a simplified representative test, which mimics the multiaxial fretting conditions between spline teeth via biaxial loading of specially-designed bridge pads and a fatigue specimen. The numerical method is based on a three-dimensional finite element model of the test rig assembly, including frictional contact effects, along with a multiaxial, critical-plane fatigue parameter for crack nucleation followed by crack growth prediction in the Paris regime using El Haddad small crack correction. The prediction methodology is shown to successfully capture the effect of the key fretting fatigue stress, which mimics the spline rotating bending moment, on total fatigue life.

Finite element simulation of fretting wear-fatigue interaction in spline couplings

This paper describes a finite element based method for simulating the effects of material removal, associated with fretting wear, on fretting fatigue parameters in a spline coupling. An incremental wear simulation technique is implemented with a single tooth finite element model of the coupling for symmetric loading, assuming equal wear on all teeth, using a comparatively coarse mesh model, for computational efficiency. A surface interpolation technique is implemented to map the predicted distributions of wear onto a non-symmetric, 360° (18-tooth) model, with detailed refinement on one tooth, to predict the effect of wear on the evolution of stress, strain and fatigue parameters and on subsequent life prediction. The life prediction is based on a critical plane multiaxial fatigue parameter approach, along with cumulative damage for combined load cycles and for wear induced changes in the fatigue parameters. Furthermore, the effect of wear due to the rotating bending moment and fluctuating torque on fretting fatigue damage accumulation is presented. Low frequency, torque and axial loading induced wear, leading to gross slip conditions on all teeth, is predicted to reduce fretting fatigue parameters and hence increase life. In contrast, higher frequency, rotating moment and fluctuating torque induced wear, corresponding to partial slip conditions, is predicted to increase fretting fatigue parameters away from the contact edges and hence lead to fretting fatigue cracking away from the contact edges and, for the case studied here, to a reduction in predicted life, as observed experimentally. The results are interpreted vis-à-vis published test data for scaled aeroengine splines.

Fretting fatigue predictions in a complex coupling

The fretting fatigue behaviour of a representative high-performance aero-engine spline coupling is studied under complex non-symmetrical and variable amplitude loads, consisting of major cycle torque and axial load, combined with minor cycle rotating bending moment and fluctuating torque. The objective of the study is to evaluate the effectiveness of finite element based predictions of: (i) a widely-used fretting fatigue damage parameter, namely a critical-plane Smith–Watson–Topper (SWT) parameter, and (ii) the fretting-fatigue-specific Ruiz criterion, for complex coupling geometries. The approach employs a high-resolution finite element model with localised mesh refinement to achieve detailed fretting fatigue results while maintaining an acceptable node count. The predictions are compared with corresponding laboratory test results and observations. Methods for overcoming the shortcomings of the SWT parameter, in the context of fretting fatigue, are discussed and a modified SWT parameter, which includes the effect of slip, is presented.

Effect Of The Coefficient Of Friction On The Fatigue Life Of Splines

The fatigue behaviour of a representative high-performance aeroengine spline coupling is investigated under test conditions designed to simulate in-service conditions. The test load cycles consist of major cycle torque and axial load, simulating maximum thrust, combined with minor cycle rotating bending moment and fluctuating torque, simulating life-limiting conditions at take-off, The objective of the study is to develop understanding of the fatigue behaviour of the coupling over a range of loading conditions, including interaction between low-cycle fatigue, fretting fatigue and fretting wear. The effect of the coefficient of friction on the fatigue life is also investigated. This information is necessary for the development of fatigue and fretting fatigue life prediction techniques. The test results are interpreted with the help of three-dimensional finite element models, which include the frictional contact between the spline teeth.

1158 軸肥大加工における適正加工条件

It was found experimentally the phenomenon that even ordinary polycrystalline metal materials such as the mild steel, copper and so on, can reveal the superplasticity-like deformation at room temperature by controlling mechanical conditions. Keeping a constant axial-compressive stress about the yield strength of the material used as the round bar, giving the round bar repeatedly an alternate stress of tension and compression by a rotating bending moment the local collar is formed in the round bar in the process of superplasticity-like deformation advances. We considered suitable condition for diameter enlarging work by changing a constant axial-compressive stress and bending angle.

An investigation of the fatigue and fretting performance of a representative aero-engine spline coupling

The fatigue behaviour of a representative high-performance aero-engine spline coupling is investigated under test conditions designed to simulate in-service conditions. The test load cycles consist of major cycle torque and axial load, simulating maximum thrust, combined with minor cycle rotating bending moment and fluctuating torque, simulating life-limiting conditions at take-off. The objective of the study is to develop understanding of the fatigue behaviour of the coupling over a range of loading conditions, including interaction between low-cycle fatigue, fretting fatigue and fretting wear. This information is necessary for the development of fatigue and fretting-fatigue life prediction techniques. The test results are interpreted with the help of three-dimensional finite element models, which include the frictional contact between the spline teeth.

ＳｉＣウィスカーＡｌ基複合材料の疲労強度

Fatigue strength of aluminum reinforced by SiC whiskers was studied under rotating bending moment at elevated temperature in air . The tests on five kinds of whisker volume fractions (0, 5, 10, 15 and 20) were carried out. The results obtained were summarized as follows;(1) The tensile strength of the composite material becames higher as the volume fraction of whiskers increases. And the tensile strength decreases with increasing the test temperature.(2) The fatigue strength at room temperature increases proportionally with the increase of the volume fraction of whiskers. The fatigue strength at elevated temperatures follows the relatonship with the volume fraction as well as the tensile strength.(3) The typical striation on the fatigue fracture surface becomes obscure and the surface becomes rougher as SiC volume fraction increase.