Showing papers on "Vibration fatigue published in 2018"

Surface integrity and fatigue lives of Ti17 compressor blades subjected to laser shock peening with square spots

Abstract: To address the effects of laser shock peening (LSP) on surface integrity and high cycle fatigue (HCF) vibration fatigue lives of Ti17 compressor blades, LSP experiments on the 1st-order bending vibration nodal region of the blades were performed by a Neodymium-doped Yttrium Aluminum Garnet (Nd:YAG) laser system with square spots. Surface roughness, in-depth residual stresses both on the pressure and suction surfaces, local bending deformations at the leading and trailing edges, and surface microstructure were analyzed by surface profiles, X-ray diffraction (XRD), three-coordinate measurement and transmission electron microscopy (TEM), respectively. HCF vibration fatigue tests were carried out on a DC-4000 electric vibration system and fatigue fracture morphologies were analyzed by scanning electron microscope (SEM). Results showed that surface roughnesses values were not more than Ra 0.4 μm both on the pressure and suction surfaces of the blades with and without LSP. Compressive residual stresses layers with about 1 mm were generated both on the pressure and suction surfaces of the blade and the maximum values were located at the topmost surface. Two-way local bending deformations induced by LSP were convex bending deformation at the trailing edge and concave bending deformation at the leading edge. High density dislocations, twinning and nano-grains were observed on the surface microstructure. Compared with as-received blades, HCF vibration fatigue lives of the blades with LSP were increased by one order of magnitude. Fatigue strengthening mechanism was implied by establishing the relationship between fatigue fracture morphologies and effects of compressive residual stresses and refined grains.

Vibration Fatigue Analysis of Carbon Steel Coil Spring under Various Road Excitations

Abstract: This paper presents the evaluation of frequency-based approach predicted spring using acceleration signals that were collected from various road conditions. Random loadings in the forms of acceleration are nominal and more flexible for vehicle components fatigue assessment. In this analysis, the strain time history of the spring and acceleration signals of the suspension strut was measured from three different road conditions. The acceleration signals were then transformed into power spectra density (PSD). PSD cycle counter, like Lalanne, Dirlik, and narrow band approach, was applied to obtain equivalent load cycles. The stress response was obtained through having the equivalent load cycles with a spring modal frequency response function (FRF) and different stress criterion, like absolute maximum principal and critical plane approaches. Then, the stress response was used to predict the spring fatigue life using stress-life (S-N) approach. The results revealed that the harshest road condition was the rural road where the spring with fatigue life of 4.47 × 107 blocks to failure was obtained. The strain predicted fatigue life was used to validate the frequency-based predictions using a conservative approach. It was found that the Dirlik approach has shown the closest results to the strain life approach, which suggested that the Dirlik approach could be used for spring fatigue life prediction with the acceptable accuracy.

Energy‐based fatigue failure characteristics of materials under random bending loading in elastic‐plastic range

Abstract: This article presents selected aspects connected to the methods of identification of strain energy density that are used to calculate the fatigue strength of materials. The authors focus on selected methods for determination of energy-based (stress-strain) characteristics of the fatigue life of materials (Wa − Nf), including a new approach for the determination of strain energy density parameter Wa. The paper also contains description and evaluation of models for determining the stress amplitudes σa in the elastic-plastic range, for bending. The developed procedure should give new capabilities in fatigue life calculations.

Methodology for assessing embryonic cracks development in structures under high-cycle multiaxial random vibrations

Abstract: The myriad applicability of the frequency-domain critical plane criterion is outlined in order to evaluate and track the progression of fatigue damage in metallic structures subjected to high-cycle multiaxial random vibrations. The fatigue assessment using the given criterion is performed according to the following stages: (i) critical plane definition, (ii) power spectral density evaluation of an equivalent normal stress and (iii) computation of the damage precursor and fatigue life. The frequency-domain critical plane criterion is validated using experimental results related to (a) AISI 1095 steel cantilever beams under nonlinear base vibration, (b) 18G2A steel and (c) 10HNAP steel round specimens under random non-proportional combined flexural and torsional loads.

The design of durability tests by fatigue damage spectrum approach

Abstract: In the present paper, a new approach to combine load conditions expressed by power spectral density functions and to synthesize them into an equivalent one was presented. This method is based on the concept of fatigue damage spectrum and on the system dynamics. It was developed to design or verify operative durability tests (i.e., tracks), able to test payloads transported by vehicles, which could be alternative to laboratory ones, defined by the norm. By analyzing the acceleration spectrum of the norm and the acceleration measurements (all expressed in terms of power spectral density functions) acquired on the designed tracks during an experimental activity conducted on a wheeled transport vehicle, it was possible to verify the goodness of the proposed approach.

Damage Monitoring of Composite Components under Vibration Fatigue using Scanning Laser Doppler Vibrometer

Abstract: This research article proposes experimental methods for monitoring damage propagation of Carbon Fibre Reinforced Plastic (CFRP) components under vibration fatigue. High cycle fatigue (HCF) behaviour of composites is often not as dramatic as that of metal alloys, where any crack initiation might rapidly lead to failure. Instead, composites HCF behaviour is often a prolonged state of continuous degradation of the resin-to-fibre bonding. Furthermore, the interlaminar contact conditions at any opening delamination cause complex dynamic responses, which can be nonlinear and temperature dependent. Vibration fatigue is generally caused by large deformations which can be suitably measured by non-contact measurement systems. Hence, this paper explores the application of the scanning laser vibrometer to monitor damage propagation of CFRP components under vibration fatigue loading. The objective is to show how this measurement system can systematically implement a set of experimental methods aimed at monitoring the dynamic properties during the crack propagation caused by fatigue. The set of experimental techniques are autonomously executed by a custom-made control panel. A thermal camera is also part of the measurement chain and provides qualitative information about location of temperature hot spots and damage evolution.

Application of a material fatigue damage model in 4PB tests

Abstract: The fatigue property of an asphalt mix is an important issue in pavement design. This property is often determined with the aid of a four-point bending (4PB) test in controlled deflection mode. The fatigue property is related to the decrease in the calculated complex stiffness modulus, however, due to the non- homogenous stress and strain field in the beam, the measured response does not represent the stiffness modulus of the material but a weighted stiffness value. For a correct interpretation, a fatigue damage material model like the Asphalt Concrete Pavement-Fatigue model is needed. After integration, the calculated and measured responses are compared. By varying the model parameters, an excellent comparison between the two responses is obtained up to a certain number of cycles. This number of cycles is denoted as the fatigue life NPH. The accumulated dissipated energy at the surface of the beam in the midsection can be expressed as a constant times the fatigue life NPH to the power z and also ...

Fatigue analysis of railway wheel using a multiaxial strain-based critical-plane index

Abstract: A fatigue damage model to assess the development of subsurface fatigue cracks in railway wheels is presented in this paper. A 3-dimensional finite element model (FEM) is constructed to simulate repeated cycles of contact loading between a railway wheel and a rail. The computational approach includes a hard-contact over-closure relationship and an elastoplastic material model with isotropic and kinematic hardening. Results from the simulation are used in a multiaxial critical-plane fatigue damage analysis. The employed strain-based critical-plane fatigue damage approach is based on Fatemi-Socie fatigue index that takes into account the non-proportional and out-of-phase nature of the multiaxial state of stress occurs when a railway wheel rolls on a rail. It predicts fatigue-induced micro-crack nucleation at a depth of about 3.7 mm beneath the wheel tread, as well as the crack plane growth orientation which indicates the possible failure pattern. Additionally, the influence of various factors such as contribution of normal stresses, higher wheel load, and material model have been investigated.

Effect of temperature on vibration fatigue of SAC105 solder material after extended room temperature aging

Abstract: Electronic products are often exposed to combined stress loading conditions (both thermal excursions and vibration) during their service life. In order to assess the performance and durability under these conditions, it is important to use temperature dependent fatigue data to assess or more accurately predict vibration damage under more realistic life-cycle conditions. This paper focuses on finding the temperature dependent vibration durability of aged SAC105 solder material. This is accomplished by using a combination of harmonic vibration tests at different temperatures and nonlinear dynamic FEA. The fatigue durability is found to decrease significantly with increasing temperature, in part due to the increase in solder strain, and in part due to degradation of the solder cyclic fatigue properties. Additionally, the room temperature fatigue results were fitted with the Basquin-Coffin-Manson fatigue model to produce the temperature-dependent model constants for the S-N curves.

Vibration fatigue tests by tri-axis shaker: design of an innovative system for uncoupled bending/torsion loading

Abstract: An innovative system for bending-torsion fatigue tests by tri-axis shaker is designed and presented. The system mounts a cylindrical specimen with eccentric tip mass, excited by horizontal and vertical base accelerations. A lateral thin plate prevents specimen horizontal displacement and allows torsional and bending deformations to be controlled independently. A lumped-mass model is first used to verify if input accelerations and resultant dynamic forces, required in testing, comply with shaker specifications. A finite element model is then used to perform both modal and harmonic analyses, necessary to determine the system natural frequencies and the dynamic response under horizontal and vertical accelerations. Experimental measures on a prototype are finally used to gather preliminary information for validating the numerical model and to verify that the proposed testing system can control bending and torsion loadings independently.

The importance of dynamic behaviour of vibrating systems on the response in case of non-Gaussian random excitations

Abstract: Dynamic response of vibrating system subjected to non-Gaussian random loads was investigated through a set of numerical simulation on several lumped systems aimed to determine whether and in what form the dynamic behaviour of a vibrating system transfers or masks non-Gaussianity features of the input to the output response. Indeed, in several numerical and experimental activities performed on a Y-shaped specimen it was observed how the system response, both in terms of displacement or stress, changed according to an input variation (stationary and non-stationary Gaussian and non-Gaussian load time histories) and according to a change of the system frequency response function. Moreover, it was observed that even if the system was excited in its frequency range, the response remains unchanged and similar to the input in case of non-stationary and non-Gaussian load, removing preliminarily the possibility to use spectral methods for damage evaluation, going necessarily back to a more “expensive” time-domain analysis. Since the system response characteristics may change significantly according to the input excitation features and to the dynamic system parameters allowing, in some cases, the use of spectral techniques for fatigue damage evaluation also in case of non-Gaussian input loads, the aim of this paper is to understand whether and how the dynamic behaviour of a generic mechanical system transforms the non-Gaussian input excitations into a Gaussian response. To this aim several numerical displacement responses of 1-dof lumped systems characterized by different frequency response functions (resonance frequency position and damping) were analysed and investigated for different stationary and non-stationary Gaussian and non-Gaussian excitations. In such a way, it was possible to a-priori establish under what circumstances the frequency-domain approaches can be adopted to compute the fatigue damage of real mechanical systems.

Application of Steinberg vibration fatigue model for structural verification of space instruments

Abstract: Electronic components in spaceships are subjected to vibration loads during the ascent phase of the launcher. It is important to verify by tests and analysis that all parts can survive in the most severe load cases. The purpose of this paper is to present the methodology and results of the application of the Steinberg’s fatigue model to estimate the life of electronic components of the EPT-HET instrument for the Solar Orbiter space mission. A Nastran finite element model (FEM) of the EPT-HET instrument was created and used for the structural analysis. The methodology is based on the use of the FEM of the entire instrument to calculate the relative displacement RDSD and RMS values of the PCBs from random vibration analysis. These values are used to estimate the fatigue life of the most susceptible electronic components with the Steinberg’s fatigue damage equation and the Miner’s cumulative fatigue index. The estimations are calculated for two different configurations of the instrument and three different inputs in order to support the redesign process. Finally, these analytical results are contrasted with the inspections and the functional tests made after the vibration tests, concluding that this methodology can adequately predict the fatigue damage or survival of the electronic components.

Device and method for detecting high-temperature vibration fatigue characteristics of aero-engine blade

Abstract: The invention provides a device and a method for detecting high-temperature vibration fatigue characteristics of an aero-engine blade. A vibration loading system is used to apply a vibration load to an aero-engine blade, and the aero-engine blade is heated and controlled by an electric induction heating system; a three-dimensional digital image correlation method is utilized to detect and analyzethe vibration fatigue characteristics of the aero-engine blade under a high temperature vibration load. The invention utilizes the three-dimensional digital image correlation method of non-contact optical full-field deformation measurement, and can adapt to measurement under various scales and various conditions; the accuracy of the detection result is ensured; vibration fatigue monitoring of theaero-engine blade can be achieved at different temperatures and different frequencies; and the comprehensiveness of the experimental result can be ensured.

Vibration Fatigue Damage Accumulation of Ti–6Al–4V under Constant and Sequenced Variable Loading Conditions

Abstract: This study aims to investigate the effect of loading factors on damage accumulation under variable amplitude vibration (VAV). Vibration fatigue experiments are conducted under both constant amplitude vibration (CAV) and VAV loading cases. The effects of loading sequence, loading amplitude, stress difference, and cyclic ratio on damage accumulation are analyzed. It is found the damage accumulation rate is strongly affected by the loading sequence: the fatigue lives can be ranked in descending order as the one-way low-high loading, the constant loading, and the one-way high-low loading. The effect of stress difference on damage accumulation is not significant, while the damage accumulation varies a lot according to the cyclic ratio of the two-level loading blocks and the fatigue life could be extended by increasing the lower loading cycles. Comparing with linear and double linear damage rules, models based on nonlinear damage rules have apparent advantages in predicting accuracy in VAV conditions, in which the nonlinear continuous damage model has the best compromise between availability and precision.

Effects of stress concentration and residual stress on vibration fatigue behavior of socket weld

Abstract: The vibration fatigue behavior in socket weld of 304L stainless steel was investigated using experimental and numerical. The vibration fatigue test results indicate that original socket weld at a h...

The relevance of non-stationarities and non-Gaussianities in vibration fatigue

Abstract: In classical fatigue of materials, the frequency contents of dynamic loading are well below the natural frequencies of the observed structure or test specimen. However, when dealing with vibration fatigue the frequency contents of dynamic loading and structure's dynamic response overlap, resulting in amplified stress loads of the structure. For such cases, frequency counting methods are especially convenient. Gaussianity and stationarity assumptions are applied in frequency-domain methods for obtaining dynamic structure's response and frequency-domain methods for calculating damage accumulation rate. Since it is common in real environments for the structure to be excited with non-Gaussian and non-stationary loads, this study addresses the effects of such dynamic excitation to experimental time-to-failure of a structure.Initially, the influence of non-Gaussian stationary excitation is experimentally studied via excitation signals with equal power density spectrum and different values of kurtosis. Since no relevant changes of structure's time-to-failure were observed, the study focused on non-stationary excitation signals that are also inherently non-Gaussian. The non-stationarity of excitation was achieved by amplitude modulation and significantly shorter times-to-failure were observed when compared to experiments with stationary non-Gaussian excitation.Additionally, the structure's time-to-failure varied with the rate of the amplitude modulation. To oversee this phenomenon the presented study proposes a non-stationarity index which can be obtained from the excitation time history. The non-stationarity index was experimentally confirmed as a reliable estimator for severity of non-stationary excitation. The non-stationarity index is used to determine if the frequencydomain methods can safely be applied for time-to-failure calculation.

Electric automobile battery pack random vibration fatigue acceleration method based on real road spectrum

Abstract: The invention discloses an electric automobile battery pack random vibration fatigue acceleration method based on a real road spectrum. The method comprises the steps of (1) acquisition and analysis of the road load spectrum; (2) calculation of full life circle fatigue damage spectrum of the battery pack; and (3) formation of battery pack vibration fatigue acceleration (laboratory standard). Electric automobile battery pack laboratory stand vibration fatigue acceleration is performed for different installing positions of different automobile battery packs according to the actually measured road spectrum of the electric automobile driving so that the problem of single evaluation standard can be solved, and the China's electric automobile operation condition can be further met on the basis of the domestic road condition and the battery manufacturing level of the domestic enterprise.

Integral dropper vibration fatigue tester

Abstract: The invention relates to an integral dropper vibration fatigue tester, comprising a rack and a body in the rack, wherein the rack comprises a main rack and a dragging rack fixed above the main rack; the body comprises an installation base plate, a driving device fixed to the dragging rack and a plurality of test units fixed between the dragging rack and the installation base plate. The integral dropper vibration fatigue tester can simulate running condition of the integral dropper and realize continuous simulation of vibration test.

Loading device used for lateral-torsional vibration fatigue experiment and method thereof

Abstract: The invention discloses a loading device used for a lateral-torsional vibration fatigue experiment and a method thereof. A sliding groove is formed in a base, brackets are installed at the two ends ofthe base, and a vibration exciter is connected to the sliding groove; the base body is connected with the brackets through bolts, rotary shafts are arranged on the two sides of a sliding sleeve, a clamping roller is installed above the sliding sleeve, and the rotary shafts are connected with a sliding seat and a shaft hole of a side plate; a guiding rod is sleeved with the sliding sleeve, and oneend of the guiding rod is connected with a loading arm; a clamping seat and a clamping head of the loading arm are opposite to each other, a V-shaped groove is formed in the clamping seat, and a second coupler is installed below the clamping seat. The loading device has adjustability and enough clamping force to ensure the stability of a platform, can provide pure torsion loading, torsion and transverse bending coupling loading, torsion and longitudinal bending coupling loading, torsion and oblique bending coupling loading and pure bending loading, has the advantages of high accuracy, high efficiency, low cost and multiple functions, and has important practical value regarding the completion of the vibration fatigue performance experiment for experimental piece materials with rectangularcross sections and circular cross sections.

Three-point bending vibration fatigue device with axial tension function

Abstract: Can only not have axial tension's three -point bending vibration fatigue to tired test piece loaded not enough in order to overcome among the prior art, the utility model provides a three -point bending vibration fatigue device with axial tension function. The application of this three -point bending vibration fatigue device can realize the three -point bending vibration fatigue experiment under the different tensile stress conditions effectively. The device is provided with and is used for the steady centre gripping subassembly of centre gripping above the support in the both ends of test piece including support and two supporting shoes that lie in a support side and be used for providing the strong point for the test piece, the both ends that lie in two supporting shoe outsides, the oneend that the centre gripping subassembly deviates from the supporting shoe is provided with and is used for driving the centre gripping subassembly for the drive assembly of support along test piece axial displacement, the support is used for supporting and is provided with the spacing subassembly that is used for rising the guide effect to the centre gripping subassembly on the side of supportingshoe.

A loading device for crumpling vibration fatigue test

Abstract: The utility model discloses a loading device for crumpling vibration fatigue test is provided with the spout on the base, the support is installed at both ends, is connected with on the spout the vibration exciter, the pedestal passes through bolt and leg joint, and the both sides of sliding sleeve are provided with the pivot and just install the pinch roll in the top, and the pivot is connected with the shaft hole of slide and curb plate, the sliding sleeve endotheca is equipped with the guide arm, and the one end and the loading arm of guide arm are connected, loading arm's relative " V " shape groove that just is provided with with the chuck of holder, the second shaft joint is equipped with to the holder below. Have the controllability, have the stability that sufficient clamping -force guaranteed the platform, can provide pure and twist reverse the loading, twist reverse with cross curvature coupling loading, twist reverse with longitudinal bending coupling loading, twist reversewith slant bend coupling loading and pure bending loading. Have high accuracy, high efficiency, low cost, multi -functional characteristics, have important practical value to the vibration fatigue capability test who accomplishes rectangular cross section and circular cross section testpieces material.

Modelling the effect of temperature on the probabilistic stress–life fatigue diagram of glass fibre–polymer composites loaded in tension along the fibre direction

Abstract: Predicting the fatigue performance of composites has proven to be a challenge both conceptually, due to the inherent complexity of the phenomenon, and practically, because of the resource-intensive process of fatigue testing. Moreover, mechanical behaviour of polymer matrix composites exhibits a complicated temperature dependence, making the prediction of fatigue performance under different temperatures even more complex and resource intensive. The objective of this paper is to provide a method for the prediction of fatigue life of glass–polymer composites loaded in the fibre direction at various temperatures with minimal experimental efforts. This is achieved by using a static strength degradation approach to fatigue modelling, where only two parameters (including static strength) are temperature dependent, in conjunction with relationships for these two fatigue model parameters temperature dependence. The method relies on fatigue data at a single temperature and simple static tests at different temperatures to predict the effects of temperature on the material’s fatigue behaviour. The model is validated on experimental data for two unidirectional and one woven glass–epoxy composites and is found to accurately predict the effect of temperature on fatigue life of composites. A method to obtain probabilistic stress-life (P−S−N)(P-S-N) fatigue diagrams including temperature effects is also presented.

Stress–cycle curves for concrete beams with fibre-reinforced polymer using runout data

Abstract: The use of externally bonded fibre-reinforced polymer (FRP) increases the fatigue life of reinforced-concrete beams due to a reduction in the steel stress level when compared with unstrengthened beams. For steel stresses up to 80% of the yield stress, fatigue failure is normally marked by the gradual deterioration of the steel reinforcement, which leads to a stress transfer to the FRP, until failure. Higher steel stresses are associated with FRP debonding, while steel stresses below the fatigue limit will never lead to fatigue failure. In this work, the maximum likelihood estimation method was used to determine stress–cycle curves and confidence intervals. Experimental data with runouts of fatigue tests found in the literature and generated through an experimental programme were used to adjust the fatigue model. The aim was to characterise the large scatter between the results of fatigue tests from different sources. The proposed fatigue model was found to represent accurately the slope of the fatigue cur...