Fatigue Test Bench Research Articles

Correlation between Numerical and Experimental Structural Resistance of a Safety Relevant Aluminum Automotive Component

Accurate implementation of weight reduction for the development of innovative safety-relevant components, such as suspension assemblies, requires a careful evaluation of the structural resistance. The validation of these critical parts usually employs Finite Element Analysis (FEA) during the design phase and laboratory tests on prototypes during later stages. However, the results of these established methods have rarely been numerically compared. The present paper introduces a method for comparing FEA and testing, based on the elaboration of micro-strains acquired with strain gauges positioned in specific regions. The model was applied to the real case study of an innovative lightweight cross beam. FEA simulations and bench tests under different conditions that were representative of the operating environments were carried out. Two different relevant configurations of fatigue bench tests were considered. Then, the data obtained from testing were numerically elaborated in order to compare them with the analytical results. Real data from in-field measurements were used. The cross beam endured at the elevate mission loads reproduced at the bench test. The FEA and testing results were aligned. The correlation method was proven to be reliable, since it made it possible not only to numerically evaluate the testing output, but also to validate the calculation tools, and it could be extended to similar applications in future.

Surface crack modelling in an engine compressor disc

This work presents two distinct procedures to perform fatigue crack-growth simulations in a high pressure compressor disc of a turbofan engine.Two distinct load cases were separately considered as applied to the compressor disc under analysis: one load case was used to replicate a full-size experimental fatigue bench test, whereas the other was used to simulate the real in service operating conditions of the engine.Two distinct approaches were adopted for the simulations: a full FEM approach and a particular variant of a FEM-DBEM submodelling strategy. It is worth mentioning that, with the latter approach, the only needed boundary conditions for the DBEM submodel analysis are tractions applied on the crack faces; such tractions are derived by the global FEM analysis.A sound agreement between numerical and experimental outcomes was obtained.

Fatigue life prediction of lightweight electric moped frames after field load spectra collection and constant amplitude fatigue bench tests

Modern mobility involves increasingly electric powered assisted vehicles; the structural integrity of a lightweight vehicle subjected to field loads for a given mission is a Fatigue Life Prediction (FLP) issue for the manufacturer: small motorcycle companies may prefer a more sustainable experimental approach to a complex a numerical approach.Aim of the present work was the fatigue life prediction of the frame of an innovative electric moped for urban commuting developed by a small manufacturer, in solo and dual riding. Given the mission adopted by the manufacturer, a load based Fatigue Life Prediction was carried out adopting an experimental approach. The moped frame and main components were strain gauged and statically calibrated to collect field load histories in solo and dual riding, including extreme driving events. Constant amplitude fatigue tests were performed on the welded tubular aluminum frame to obtain the fatigue curves at the steering tube node under horizontal loads (N = 8) and at the rear seat support node under vertical pulsated seat loads (N = 8). Measured field load spectra were extended to the design mission and used to predict the minimum required Virtual Load Life Curve (VLLC) able to guarantee the target mission life. A damage summation value appropriate to welded aluminum structures was adopted. The comparison of the Virtual Load Life Curve and the real component fatigue curves enabled to evaluate the frame durability safety factors in the two considered loading conditions and to check the validity of redesign solutions for the weakest component locations.

Manufacturing and Evaluation of Multi-Material Axial-Bearing Washers by Tailored Forming

Components subject to rolling contact fatigue, such as gears and rolling bearings, are among the fundamental machine elements in mechanical and vehicle engineering. Rolling bearings are generally not designed to be fatigue-resistant, as the necessary oversizing is not technically and economically marketable. In order to improve the load-bearing capacity, resource efficiency and application possibilities of rolling bearings and other possible multi-material solid components, a new process chain was developed at Leibniz University Hannover as a part of the Collaborative Research Centre 1153 “Tailored Forming”. Semi-finished products, already joined before the forming process, are used here to allow a further optimisation of joint quality by forming and finishing. In this paper, a plasma-powder-deposition welding process is presented, which enables precise material deposition and control of the welding depth. For this study, bearing washers (serving as rolling bearing raceways) of a cylindrical roller thrust bearing, similar to type 81212 with a multi-layer structure, were manufactured. A previously non-weldable high-performance material, steel AISI 5140, was used as the cladding layer. Depending on the degree of forming, grain-refinement within the welded material was achieved by thermo-mechanical treatment of the joining zone during the forming process. This grain-refinements lead to an improvement of the mechanical properties and thus, to a higher lifetime for washers of an axial cylindrical roller bearing, which were examined as an exemplary component on a fatigue test bench. To evaluate the bearing washers, the results of the bearing tests were compared with industrial bearings and deposition welded axial-bearing washers without subsequent forming. In addition, the bearing washers were analysed micro-tribologically and by scanning acoustic microscopy both after welding and after the forming process. Nano-scratch tests were carried out on the bearing washers to analyse the layer properties. Together with the results of additional microscopic images of the surface and cross-sections, the causes of failure due to fatigue and wear were identified.

Justification of parameters of wheelset axle fatigue strength test-bench for railway rolling stock

The operation safety of the railway rolling stock depends directly on the strength of the base part of the wheelset – its axle. Therefore, in recent years numerous studies of theoretical and experimental nature, both for means of rail transport, and for machines containing rail track equipment are carried out. This paper substantiates the main parameters of the fatigue test bench for axles for wheelsets of railway rolling stock. We performed an analysis of the load schema for bench tests, determined the dependence of the bench work force on the parameters of the wheelset axle. In addition, we substantiated the design and parameters of vibrator. For the research, we adopted the following criteria of rationality: work force, energy consumption and longitudinal dimension of the test bench. The design is considered the best, if these criteria acquire the smallest values. The results of the research indicate that the load scheme “cantilever beam” is rational for the fatigue bench tests of the axles for wheelsets of railway rolling stock. The best design of the vibrator have to provide the test bench work force by rotating the unbalanced mass around the stationary wheelset axle. The rational vibrator contains a sectoral eccentric mass rotating at an angular velocity of about 150 s-1. In this case, the eccentric mass value is about 80 kg, and its eccentricity is 135 mm.

Fatigue strength evaluation for individual strands of overhead conductors using a biaxial fretting fatigue test bench

This paper presents a biaxial fretting fatigue test bench which provides the capability of performing fretting fatigue experiments on individual wires of a conductor combining the effect of both alternating tension and bending loadings to represent a more realistic state of a conductor individual strand under periodic loading caused by aeolian vibrations. Preliminary tests with only uniaxial alternating tension loading were carried out on 1350-H19 aluminum wires having the same mechanical and geometric characteristics as those of the ACSR Bersfort conductor aluminum strands. Different levels of alternating stress were tested in order to validate the performance of the apparatus. Preliminary results showed that the experimental setup allows reproducing the local loading state which leads to the fretting fatigue damage on the tested wires. Biaxial tests were also conducted at a high level of alternating loadings. The results of these tests reveals that, at high alternating stress amplitudes, the biaxial loading allows to observe some fretting fatigue failures, whereas early plain fatigue failures were observed when applying similar uniaxial loading.

Research on Fatigue Test Method of Car Body for High-speed trains

The car body of high-speed train bears all the static and dynamic loads. An accurate strength analysis of critical point is crucial for its fatigue design. Since a fatigue analysis is dependent on the load amplitude and its application point on car body, the loads applied in the fatigue test is studied by using the strength test bench. A comparative study was performed among the relevant standards concerns the car body fatigue. In addition, a specific test scheme is promoted, and the applied loads on vertical, lateral, longitudinal and torsional directions on car body under various spectrums are thoroughly determined. This study provides a basic fatigue test bench of car body for high-speed trains with the specific loads application and test schemes. This allows the body to be subjected to random loads and provides a basis for the specifications of follow-up fatigue tests on the car body and its components.

Fatigue analysis and experiment of leaf-spring pivots for high precision flexural static balancing instruments

For distributed-compliance flexure mechanisms, their service life is affected by fluctuating stress which may result in fatigue failure, but only static failure was taken into consideration in most studies. As one of the best-known types of distributed-compliance flexural pivots, the cross-spring pivot applied to the flexural static balancing instruments is subjected to large enough vertical loads and fluctuating stresses. In this paper, the cross-spring pivot is taken to explore the methods of prolonging its fatigue life, and the methods can be extended to the other pivots based on leaf-springs. Meanwhile, another important performance of the pivot-the rotational stiffness remains unchanged. Firstly, in order to develop a stress-life model, the equivalent fatigue stresses of the cross-spring pivots are derived in which the stress concentration factors are obtained by fitting the finite element results. Then, two methods for prolonging the fatigue life of the pivot are proposed, i.e., increasing the ratio of length to thickness of leaf-springs and reducing stress concentration. To verify the theoretical analysis, the fatigue life of five cross-spring pivots with the same rotational stiffness is tested based on a developed fatigue test bench. Experimental results show that the fatigue life of the cross-spring pivot can be prolonged, which verifies the validity of the two methods.

Design of a fatigue test bench in rotary flexion to evaluate the behavior to cyclical loads

The development of this article shows the process of design, construction and start-up of a fatigue machine in rotary flexion. Fatigue is a subject of considerable relevance and requires adequate equipment for its study, therefore it is sought to contribute to educational and research growth through the development of a functional fatigue machine and where a variety of materials can be studied. The main results were the development of a machine that can carry out a totally inverted stress of 977 Mpa, therefore it can arrive to study steels of high resistance. This machine follows the standards of the normative ASTM E-466 regarding the dimensions of the test specimen. The design of the machine is divided into 3 systems, mechanical system, electrical system and electronic system. When joining these systems obtained a functional and autonomous machine where can make serious and reliable investigations.

An Experimental Study of Laser in situ Fenestration of Current Aortic Endografts

Laser in situ fenestration (LISF) is emerging as an immediately available alternative in the endovascular treatment of complex aortic aneurysm. However, its biomechanical features remain poorly understood. The aim of this study was to experimentally evaluate textile damage secondary to LISF and to compare LISF with mechanical in situ fenestration (MISF). An invitro study evaluated the damage created by LISF on endograft fabrics versus MISF using a needle. Five different models of commercially available aortic endografts were used (32 samples of polyethylene terephthalate and expanded polytetrafluoroethylene fabrics). Tensile strength tests were performed on the fabrics before and after in situ fenestration, to determine the loss of mechanical strength. Integral water permeability tests at the stent-fenestration interface evaluated the watertightness of junctions. Stability of the connection was assessed with a fatigue bench test flexing the branch on the fenestration. In a second step, an invivo study evaluating LISF in sheep was conducted. Resulting holes had circular and cauterised edges following LISF, whereas fabric filaments were pushed aside after MISF. Tensile tests demonstrated a 34% and a 27% mechanical resistance loss after LISF (p=.004) and MISF (p=.001) compared with non-fenestrated samples. A non-significant global decrease of 7% in mechanical resistance was found following LISF compared with MISF (p=.520). Water permeability tests highlighted that leak rates were higher following LISF than with MISF with regard to multifilament specimens (p<.05). Fatigue tests induced modification of the morphology of fenestrations. The surface area of the fenestration was increased for all samples after 170,000 cycles. Regarding the invivo study, 14 LISF were performed in 12 sheep with a technical success rate of 88%. This study demonstrates that both LISF and MISF create substantial damage to all available endograft fabrics. Until comparisons with reinforced fenestrations are performed, LISF and MISF should not be used outside investigational studies.

Lightweight of a cross beam for commercial vehicles: Development, testing and validation

Commonly the reduction of weight in transport is applied to passenger cars, while commercial vehicles are still not widely involved due to structural and costs restraints. This research studied a new concept of aluminium cross beam suspension for commercial vehicles that would replace the currently used steel component. The related advantages entail the achievement of an affordable solution, weight reduction of about 50%, environmental benefits, avoidance of painting and excellent recyclability. The use of appropriate materials, a new concept of design and a careful function integration allowed the structural limits to be overcome. The feasibility of this solution was verified through detailed characterisation and testing, composed of an analysis of the most relevant failure modes, with microstructures, hardness tests, tensile tests, fractography, salt spray test and fatigue test bench road simulator with field test data. The validation was successfully completed and the feasibility of the light alloy use for this particular heavy application was demonstrated. Further experiments, based on the development of heat treatments for potential future extension of this application, were conducted with the support of Design Of Experiment methodology. The outputs constitute a useful database of properties.

Multi-axial fatigue life assessment of high speed car body based on PDMR method

This article mainly introduces a method of converting the acceleration signal of body bolster obtained by the circuit test into the load of the air spring seat of vehicle body. This method mainly decomposes the body's movement posture into the form of ups and downs, roll and nod. Then formulate the test plan according to the performance of the body fatigue test bench. The vertical and horizontal displacements and longitudinal force are used as control commands.Taking advantage of vehicle body fatigue test bench to reproduce these basic types of vibration. Establish the transfer function of the acceleration of the bolster and the displacement excitation of the air spring, and then obtaining the load of the air spring seat. Finally, the multi-axial fatigue life assessment of the vehicle body was performed using the obtained load combined with the Moment of Load Path Method and the Path-Dependent Maximum Range Method.

Influence of the Notch Radius on Fatigue Crack Propagation in Beam Specimens of 2017A-T4 Alloy

We present experimental results on the fatigue crack growth in specimens with rectangular cross sections made of 2017A-T4 aluminum alloy under bending. The specimens were weakened by sharp and blunt one-sided notches (for the notch root ρ = 0.2; 5; 10 and 22.5 mm). The tests were performed on a MZGS-100 fatigue test bench in the low- and high-cycle fatigue modes by imposing a constant value of the nominal load ratio R = – 1; 0 and a moment amplitude M a = 15.84 N·m. The results of fatigue tests were then analyzed in terms of the parameter ΔK including the influence of the notch.

Fatigue reliability design of composite leaf springs based on ply scheme optimization

The study of composite leaf springs has been popular in automotive light weighting. Particularly, the research on the fatigue reliability of composite leaf springs is crucial. This paper proposed the fatigue law inference of the parabolic composite leaf spring, which was validated by fatigue bench tests. On the bases of the ply scheme design method and the sandwich unit concept, the non-continuous layer section and the stacking order were presented. The stacking sequence was optimized using Genetic Algorithm. The production of composite leaf spring samples, on which the fatigue bench test was conducted, was based on the optimized ply scheme. Results indicate that the fatigue life of composite leaf springs can be improved by using the proposed ply scheme design method.

Resonant fatigue test bench for shaft testing

AbstractShaft fatigue testing involves long test times (~3 months), high energy consumption and high test equipment maintenance costs owing to the high bending and twisting moments required (~1600 Nm), high number of cycles (~107) and large sample sizes (~30).To reduce testing time, we designed, manufactured and evaluated a resonant plate test bench. Using finite element analysis and topological optimization, we redesigned the traditional resonant flat plates for higher resonant frequency and lower deflection at the plate free ends. We found that the optimal topology is an I‐beam; it doubles the frequency of flexion tests, up to 100 Hz, and exhibits 2 mm of deflection under a load of 1 kN.To measure the moments induced on the shaft sample during testing, we measured the surface deflection of the resonant plates. Tests on a calibration axle showed that the induced shaft moment has very high linear correlation (R2 &gt; 0.99) with the plate's surface deformation.We used our test bench to evaluate fatigue resistance for a type of crankshaft manufactured by a local company. We found that their fatigue resistance limit was 1250 Nm at 107 cycles and that their mean useful life was 104 cycles when they are subjected to a 1400 Nm moment. These results agree with previous results on this type of crankshaft using other methods.

English

Bearing is an important component of a rotating machine; however, under normal operating conditions, it is subjected to fatigue which results in a defect called spalling. This work presents a monitoring fatigue of a thrust ball bearing on a bearing fatigue test bench. Spalling is artificially initiated on a bearing raceway. Vibration analysis is the method used to characterize the defect. The experimental procedure used is to monitor the operation of the ball bearing to the degradation with an online acquisition of the vibration readings. These data allow plotting the curve of fatigue (mathematical model). In order to obtain more realistic curve, the spalling evolution of several thrust ball bearings is monitored, first, under different loads then at different rotation speeds under a constant load. It found that growth follows a spalling power law and the damage is characterized by the model parameters. &nbsp; Key words: Predictive maintenance, bearing, vibration analysis, spalling, rolling fatigue. &nbsp

Effect of Constitutive Model on Thermomechanical Fatigue Life Prediction

In this paper, thermomechanical fatigue life (TMF) prediction is performed on an automotive exhaust manifold using in-house postprocessor code (Hotlife) with four different constitutive models: elastoplastic model with kinematic hardening, two-layer viscoplastic model, and two unified elasto-viscoplastic models based on the equations proposed by Sehitoglu and Chaboche, respectively. Commercial FEA software Abaqus has been used for the analysis. The first two models are already available in Abaqus; the Chaboche and Sehitoglu models were implemented using a user material subroutine (UMAT, available in Abaqus). The stress and strain histories calculated by these four models are output to Hotlife for post-processing. The results from the prediction are then compared to the experimental TMF life obtained from a component thermal fatigue bench test. Result show the Hotlife calculations based on the two implemented elasto-viscoplastic models yield better correlation with test results.

A Novel Methodology with Testing and Simulation for the Durability of Leaf Springs Based on Measured Load Collectives

In this study, the aim is to present the newly developed testing and simulation method for the durability of leaf springs in order to direct designers in the product development phase. The load spectra, which contain the variable amplitude loading to determine the fatigue life, were measured from different vehicles on rough road testing track. Afterwards, accelerated spectra were generated for testing and used in newly built fatigue test bench. Also, Finite Element Method (FEM) and Multi Body Simulation (MBS) calculations were performed and load spectra were processed with multi-channel fatigue life calculation to generate a virtual test rig.

Fatigue testing of flexure hinges for the purpose of the development of a high-precision micro manipulator

Abstract. An approach was initially proposed for the estimation of the maximum von Mises stress in flexure hinges. It relied on recognizing relevant stress factors that were calculated from empirical functions set up by using the finite element method. Afterwards, a fatigue test bench was designed and realized for the examination of flexure hinge specimens. As functional failure occurred before fracture, crack initiation and propagation were observed permanently with the help of a monitoring system and sporadically by means of scanning electron microscopy. On the basis of results obtained thereby, where varying the maximum rotation angle, the operating frequency and the quality of the notch surfaces, a correlation was established between the stress limit and the number of cycles up to functional failure. This was utilized for the optimal dimensioning of flexure hinges within the framework of the development of a high-precision micro manipulator.

Microstructure-sensitive accumulation of plastic strain due to ratcheting in bearing steels subject to Rolling Contact Fatigue

It is well known that the empirical parameters correlated to Rolling Contact Fatigue (RCF) bench tests are sensitive to the microstructural attributes of the bearing material. The key driver for this sensitivity is the accumulated deformation accentuated by the difference in the mechanical properties of the carbide precipitate, matrix, and interface. This manuscript studies the accumulation of deformation/micro-plastic strain during RCF due to ratcheting behavior in the microstructure of bearing steels. The objective of this study is to understand the contribution of carbide particles towards ratcheting. Homogeneous elastic–plastic finite element (FE) simulations of the ball-on-rod RCF test using a ‘global–local’ approach is used, and is applicable when the drivers for fatigue degradation are controlled primarily by the heterogeneous field represented by the carbides. The global model simulates the overall ball-on-rod RCF test considering homogeneous material, while the local model accounts for the influence of the carbide particles in the microstructure. The results from finite element simulations reveal that carbide particles act as stress concentrators and introduce a shear stress cycle with a non-zero mean stress at the scale of the carbide microstructure, which promotes strain accumulation via ratcheting. A study on the spatial variation of ratcheting behavior in the vicinity of the carbide particle is also presented. The results presented translate to other through and case-hardened bearing steels subject to RCF and highlight the important role played by the carbide microstructure in controlling the spatial and temporal rate of fatigue damage accumulation via localized ratcheting. The approach presented has general applicability to heterogeneous materials with other forms of heterogeneity such as inclusions, pores and grain boundaries, subject to multiaxial fatigue.