Fatigue Life Of Spring Research Articles

Surface Residual Stress Release Behavior of Shot-Peened Springs

Shot peening is the primary method used to improve the fatigue life of springs. In this study, we aimed to quantify the reduction in residual stresses in the shot-peened layer by considering factors such as surface roughness, cyclic loading, and the helix angle, based on the spring’s periodic variation and curvature characteristics. We developed an equivalent replacement algorithm to address the challenge of characterizing the dynamic accumulation and attenuation of residual stresses under cyclic multiaxial stresses. This algorithm accurately modeled the dynamic attenuation of residual stresses and was incorporated into the spring life prediction model. Experimental validation demonstrated the high accuracy of the model for predicting fatigue life.

Fatigue Life Assessment of Automotive Leaf Springs

The creation of a new mechanical component, such as a high-performance leaf spring, is a very challenging procedure that consists of many stages over a long timeframe from concept to production. High performance leaf springs are components with high complexity at the areas of failure. This complexity is derived from the multiple manufacturing processes that the raw material undergoes to reach its final geometrical and microstructural form. The paper shows the assessment of fatigue life of high-performance leaf springs, from different manufacturers with different geometrical and loading parameters. The assessment uses the fatigue life calculations which are described at the FKM Guideline as a basis. Limitations of the FKM Guideline, concerning the material’s ultimate tensile strength and the exclusion of the stress shot peening process, are restricting the fatigue life calculations of such components, therefore, a new theoretical tool is needed for more accurate calculations.

An Experimental Investigation of Fatigue Performance for A Flexure Spring

In order to prevent a free-piston Stirling cryocooler failure during mission life, the flexure spring's fatigue life is most critical and important. In the current research, an effort is made to examine fatigue life. The fatigue life testing of cryocooler flexures is frequently discussed in the literature. However, more information is needed about the economic approach and hardware needed for the testing. This research paper adopts the FEA approach of flexure spring and outlines the criteria for flexure fatigue testing. A moving coil linear motor was also designed and selected for the oscillating shaft and bending special-purpose flexure spring stack to validate stiffness criteria. The 108 no. of cycles required to validate the fatigue limit were also attained using the approach in a few days when testing at a relatively high frequency.

Effects of rolled fibrous microstructure on fatigue properties of extruded Cu-5Al planar micro springs

Planar micro spring is an important elastic component in microelectromechanical system devices, and one of its main failures is fatigue. In this work, a new method to improve the cycles of a planar micro spring by introducing pre-rolled fibrous microstructure was proposed. Cu-5Al alloy billets with a fibrous microstructure rolled at room temperature with a reduction ratio of 70% were obtained. Three types of planar micro springs with fibrous microstructure were prepared through extrusion by varying the angle between the fibrous microstructure direction and the extrusion direction. Fatigue tests were conducted using a customized micro-fatigue test system. The best fatigue performance was obtained by preparing the micro springs with the fibrous microstructure direction perpendicular to the extrusion direction, while the worst fatigue performance was obtained by preparing the planar micro springs with the fibrous microstructure direction parallel to the extrusion direction. The fibrous microstructure direction affected the local strain in the micro springs. The fibrous microstructure slightly affected the location of the crack initiation region but significantly affected the area of crack initiation and steady-state expansion region of the micro spring. The fatigue life cycle of extruded Cu-5Al alloy planar micro spring with the pre-rolled fibrous microstructure improved by 58% more than that of extruded Cu-7Al alloy planar micro spring without the pre-rolled fibrous microstructure. Micro spring fatigue life cycle decreased with increasing strain amplitude. This work provides a new approach for preparing planar micro springs with high fatigue performance.

Simulation analysis of effect of wheel out-of-roundness on dynamic stress of coil springs in metro vehicles

Many Chinese metros experienced numerous fatigue failures of the coil springs in the suspension of vehicles. The field test results presented in our previous work showed that wheel out-of-roundness (OOR) was responsible for the failure of the coil springs. It is believed that the most effective countermeasure to eliminate wheel OOR is to reprofile wheel. The fatigue life of coil springs is an important reference for determining the reprofiling parameters. A sophisticated vibration model for train and track with flexible coil springs and flexible track was established and validated with field test results. The effects of wheel OOR and P2 resonance on the coil spring can be evaluated with this model. The relationship between wheel OOR and coil spring dynamic stresses was determined using multibody simulation (MBS). The fatigue life of the coil springs was evaluated using the parameters of the amplitude of the wheel OOR and the mileage. Under the premise of finding a balance between improving the service life of the coil springs and reducing the cost of reprofiling the wheel, viable proposals were made to solve the problem of coil spring fracture.

EFFECT OF SHOT PEENING DURATION ON FATIGUE LIFE OF GALVANIZED AND NON-GALVANIZED PEARLITIC HIGH STRENGTH HELICAL COMPRESSION SPRINGS

In this study, the effect of shot peening duration on the fatigue life of galvanized and non-galvanized springs was investigated. As the shot peening duration increased, the fatigue life of the compression springs decreased due to several embrittlement mechanisms on the spring surface. The surface roughness almost linearly increased with increasing shot peening durations. The best fatigue life was obtained with shot peening durations of 10 and 20 min for non-galvanized and galvanized springs, respectively. The non-galvanized specimens exhibited better fatigue performance than galvanized springs. The main reason for the decrease in the fatigue performance of galvanized springs is hydrogen embrittlement behavior. Free hydrogen generated in the acid bath during the galvanizing process is entrapped between the surface and the zinc layer. As a result, the compression strain that reflects crack onset and propagation was adversely affected by hydrogen embrittlement behavior.

Experimental validation of multiaxial fatigue theories to estimate fatigue life of helical compression spring

High-stress amplitudes and mean stress cycles are expected to be endured by helical compression springs utilized in a two-suspension wheeler's system. Fatigue failure of all these springs brings enormous eventual repair and replacement costs. A fatigue test is conducted to ascertain fatigue strength. The spring test plan is rather extensive due to the limited time and numerous test spring versions. Efforts were made to anticipate the helical spring's fatigue life. Multiaxial fatigue theories are examined in this work. The research paper aims to scrutinize the appropriate techniques that spring manufacturers should employ in the planning stage to calculate the fatigue life of helical compression springs. The criteria of Wang & Brown, Fatemi & Socie, Mitchell, Baumel & Seeger, and Smith & Watson are used in the present investigation. The results of the experiment and the predicted life are compared. Spring fatigue life is overvalued by the Wang-Brown criterion, while the Fatemi-Socie model offers a precise forecast of fatigue life.

Effects of Mean Stress and Multiaxial Loading on the Fatigue Life of Springs

In this paper, the effects of mean stress and damage accumulation on the fatigue life of springs are theoretically studied. The study examines the fatigue life of homogeneously stressed material subjected to cyclic loading. The mean stress of a load cycle is non-zero. Goodman and Haigh diagrams are commonly used for estimating fatigue life in engineering applications. Alternatively, conventional hypotheses by Smith–Watson–Topper, Walker and Bergmann have been successfully used to describe uniaxial cyclic fatigue with non-zero mean value over the whole range of the fatigue life. However, the physical characteristics of the mean stress sensitivities in these hypotheses are different. The mean stress sensitivity according to Smith–Watson–Topper is identical for all materials and stress levels. This weakness reduces the applicability of the Smith–Watson–Topper parameter. At first glance, the mean stress sensitivities according to Walker and Bergmann are diverse. The mean stress sensitivities depend upon two different additional correction parameters, namely the Bergmann parameter and the Walker exponent. The possibility of fitting the mean stress sensitivity in these hypotheses overcomes the significant drawback of the Smith–Watson–Topper schema. The principal task of this actual study is to reveal the dependence between the Bergmann parameter and the Walker exponent, which leads to a certain mean stress sensitivity. The manuscript establishes the simple relationship between both fitting parameters, which causes the equivalent mean stress sensitivity for the Bergmann and Walker criteria. As known from the state of the technology, fabrication and operation yield several impacts with a significant influence on the fatigue life of springs. One effect deals with the sequence of low and high stress amplitudes and amplitude-dependent damage accumulation. Particularly, during the load cycle a certain microscopical creep occurs. This creep causes damage. The accumulation hypothesis for creep damage is introduced. The hypothesis can be verified experimentally.

Fatigue life prediction of eccentric springs for the automobiles considering residual stress

AbstractSprings are widely used in the automobile industry. They can produce large elastic deformation under the action of load. The fracture failure of springs will cause significant loss or maintenance costs. The fatigue life of springs is greatly affected by load eccentricity and residual stress. Some existing methods are not accurate enough to predict the life of springs. The cracked spring stresses are computed considering load eccentricity. Based on the Walker model, a method for predicting the spring fatigue life is proposed. The model combines the superposition principle and the closure effect, and it can consider residual stress, crack closure effect, and load eccentricity at the same time. The results demonstrate that the improved model has a better performance than the Walker model.

Fatigue Life Modelling of Steel Suspension Coil Springs Based on Wavelet Vibration Features Using Neuro-Fuzzy Methods

This study proposed wavelet-based approaches to characterise random vibration road excitations for durability prediction of coil springs. Conventional strain-life approaches require long computational time, while the accuracy of the vibration fatigue methods is unsatisfactory. It is therefore a necessity to establish an accurate fatigue life prediction model based on vibrational features. Wavelet-based methods were applied to determine the low-frequency energy and multifractality of road excitations. Strain-life models were applied for fatigue life evaluation from strain histories. ANFIS modelling was subsequently adopted to associate the vibration features with the fatigue life of coil springs. Results showed that the proposed wavelet-based methods were effective to determine the signal energy and multifractality of vibration signals. The established vibration-based models showed good fatigue life conservativity with a data survivability of more than 90%. The highest Pearson coefficient of 0.955 associated with the lowest RMSE of 0.660 was obtained by the Morrow-based model. It is suggested that the low-frequency energy and multifractality of the vibration signals can be used as fatigue-related features in life predictions of coil springs under random loading. Finally, the proposed model is an acceptable fatigue life prediction method based on vibration features, and it can reduce the dependency on strain data measurement.

Fatigue analysis of coil springs in the primary suspension of a railway vehicle based on synthetic spectrum for time-varying vibration load

The fatigue life of coil springs is usually predicted with a stationary Gaussian vibration load and deterministic structural parameters. However, the obtained fatigue life is inconsistent with the observed fatigue life of fractured springs which varies within a wide range. The work aims to propose a method to predict the fatigue life of the coil spring by considering the time-varying vibration load, i.e., root mean square (rms) varies with time and the uncertainties of geometric parameters. First, a synthetic method for time-varying vibration loads is proposed. The time-varying load is decomposed into multiple stationary Gaussian short samples represented by their power spectral density (PSD). These PSDs are synthesized according to the distribution characteristics of spectral values, in which data that are non-Gaussian are processed with the Johnson system. Second, the influence of parameter uncertainties in the coil spring is studied by a Monte Carlo analysis of the stress frequency response function. Finally, the fatigue life is calculated and compared with the results predicted by using the measured stress. The results show that the synthetic spectrum has almost the same damage potential as the measured time-varying load. In comparison with results predicted from the measured stress, the synthetic spectrum gives much better estimates of the fatigue life of the coil spring than the average spectrum. Parameter uncertainties of coil springs significantly affect fatigue life and should be taken into account.

Prediksi Umur Lelah Pegas Ulir Suspensi Depan Minibus yang dikemudikan di Atas Permukaan Jalan Datar, Menanjak dan Menurun Berazaskan Pendekatan Strain-Life

This study aims to evaluate the effect of road conditions on the fatigue life of coil springs using the strain life approach. This approach is accomplished by measuring the strain signal in the coil spring at the front of the car with a strain gauge at the component's critical point. Three different types of roads, namely flat roads, uphill roads, and downhill roads were chosen to test the strain signals obtained. After analysis, it was found that the fatigue life of the coil spring on the downhill road had the lowest value of 1.52e+4 cycles before it broke. This value is 54% lower than the fatigue life on flat roads and 96% lower than on uphill roads. This result is due to the braking factor on the way down which puts a higher tension on the coil springs, reducing their fatigue life. This study can contribute to the automotive industry to consider different road conditions in the design and testing of their products, especially in critical components such as coil springs. The strain life approach has also been shown to be effective in evaluating the fatigue life of automobile components, which can help improve vehicle quality and safety.

Prediksi Usia Kelelahan Pegas Ulir dan Lower Suspension Arm Berdasarkan Pendekatan Strain Life Berdasarkan Bentuk Permukaan Jalan

This study aims to determine the effect of road surface contours on fatigue life of coil springs and lower suspension arm. In this study, strain gauge was affixed to the critical point of the minibus front suspension coil springs based on stress distribution. Strain signal obtained was analyzed using the Coffin-Manson, Morrow, and SWT approaches. From the results of the chemical composition test, it was found that the coil springs were made of SAE 5160 and lower suspension arm made of AISI 1513. From the results of this study it can be concluded that when the vehicle drive on the damaged road, coil spring and lower suspension arm received greater stress so that provide shorter fatigue life. Fatigue life of coil spring on rough roads is 16% lower than city roads and 7% lower than flat roads. Whereas fatigue life of lower suspension arm on rough roads is 27% lower than city roads and 0.03% lower than flat roads. So that the coil spring components fail faster than the lower suspension arm. This is because the contour of the road surface provides a vertical load so that it is in accordance with the function of the coil spring which works to reduce the load vertically while the lower suspension arm function holds the load when turning.

On the need to evaluate the probabilistic of fatigue life assessment of random strain loading considering load sequence effects

This study presents a probabilistic method of fatigue life assessment for random strain signals that consider the effect of load cycle sequences. The Effective-Strain-Damage (ESD) model was utilised to calculate the fatigue life of coil spring. The probabilistic approach was used to evaluate the reliability properties of the fatigue life data, indicating that the ESD model estimated lower fatigue life than conventional strain-life models as the load sequence effect encouraged rapid crack propagation. Furthermore, a lower mean-cycle-to-failure (McTF) of 4.53 × 104 blocks to failure was estimated from the ESD-based fatigue life, as it was 7.5–8.1% lower than the McTFs computed from the fatigue life predicted by other models. The results indicated that the coil springs had lower fatigue reliability when the load cycle sequence was included. The McTF can be used as a representation of the reasonable service cycle of the coil spring since the uncertainties of the random loading were considered. Finally, this approach suggested a more appropriate assessment of the life cycle of coil springs subjected to random loading conditions with many uncertainties.

Influence of the surface flaws in oil-tempered wires on the fatigue life of automotive engine valve springs

The purpose of this study is to evaluate the fatigue life of an automotive engine valve spring when the micro defect is applied to a 2300 MPa-class oil-tempered wire (OT wire) with 2.5 mm of diameter as the critical flaw depth. First, the deformation of the surface flaws in the OT wire during the valve spring manufacturing processes was derived via FE analysis using the sub-modeling technique, and the residual stress of the final spring was measured and applied to the spring stress analysis model. Second, the strength of the valve spring was analyzed to examine the presence of residual stress and compare the applied stress levels by the surface flaw. Third, the influence of micro defects on the fatigue life of the spring was evaluated by applying the stress on the surface flaw derived through the spring strength analysis to the S–N curve derived through a rotary bending fatigue test with the OT wire. The flaw depth of 40 µm, which is the existing criterion for surface flaw management, does not reduce the fatigue life.

Primary suspension failure analysis in FIAT type LHB bogies and life estimation

Multiple cases of failure in the primary suspension system of LHB coaches were reported in specific light-weight passenger coaches recently. Frequent failure in suspension systems led to increased downtime and maintenance costs. Failure was associated to fatigue in primary helical springs and was found to be preceded by failure of hydraulic dampers. We present a study on analysis of these failures and suggest design modifications for enhancing fatigue life. A flexible finite element model of the bogie, with suspension system involving flexible helical springs, is developed and simulated for typical load and vehicle speed parameters. Conditions of damper failure are incorporated and the exact location of failure and the observed fatigue life of spring are validated. Loading on the bogie involves tare weight and rail-wheel contact forces. Rail-wheel contact forces are computed through multibody dynamic model for typical track irregularity data. Linear static analysis is done to obtain stresses under steady loads. This is followed by pre-stressed modal analysis and harmonic response simulation of the flexible model of the bogie. Fatigue life computation under combined static and alternating load conditions is done by employing the Modified Goodman diagram. Iterative modifications in design of the primary suspension springs are carried out. Minimal changes, which do not require change in the designs of associated components or change in the manufacturing set-up, are suggested. Modifications are validated through comparative fatigue life estimation.

Development of non-linear models to evaluate the NiTi SMA spring actuator

The shape memory alloy (SMA) based actuators are replacing huge and bulky actuators because of its ability to provide high work per unit mass and serves as active prismatic joint to develop precise robotic manipulators. It also helps in developing a light weight manipulators with a simple actuation process. Here, the study presents the relationship between the contraction of Nitinol SMA prings and the input variables such as current and time to effectively interpret the behavioural complexity. In addition, the response of two Shape memory alloy springs in series combination has been discussed. The finite element analysis (FEA) of the SMA wire and spring has also been carried out to predict the fatigue life of SMA wire and spring. The result showed that the contraction rate of SMA spring increases with increase in current and vice-versa. Moreover, the range of current is classified based on its significance. The relationship of current, displacement and time parameters, during the actuation of SMA spring, is a second order polynomial regression model. The applied current and time have positive impact on the contractiong rate of SMA. Several polynomial regression models were developed in order to predict the precise amount of spring actuation. This study also predicts the range of current suitable for its actuation based on its application as actuator. The FEA result shows that the SMA springs can have high endurance stress limit which makes it unique as compared to other commercially available actuators. This study enables to predict the rate of contraction and the deflection trend of SMA based actuators for precise positioning applications.

Effects of the angle between the spring arm on spring characteristics on the single coiled torsion spring using Ti-Ni shape memory alloy wire.

We have been investigated one-coil torsion springs using shape memory alloy (SMA) wire for application to welfare equipment (for example, lower limb orthoses), because one-coil torsion springs using SMA wire have small size and large displacement. It is known that the spring properties of a torsion spring depend on the shape of the spring, and design calculation method for springs made of normal metals have already been established. However, SMA has different characteristics from normal metals, and it is difficult to apply conventional design calculation methods. Therefore, we fabricated several SMA torsion springs with different the angle between the spring arm and investigated the effects of shape of the spring on the spring characteristics of SMA torsion springs by spring characteristic tests and fatigue tests. The experimental results show that increasing the angle between the spring arm improves the fatigue life of the SMA torsion springs but the spring generating force decreased. On the other hand, the functional degradation characteristics are independent of the angle between the spring arms.

Effect of the galvanization process on the fatigue life of high strength steel compression springs

Abstract In this study, a compression spring fatigue problem arising from the galvanization process was investigated. Fatigue, crack initiation and growth of galvanized and non-galvanized springs manufactured from fully pearlitic high strength steel wires were investigated. According to the results, the galvanized compression springs exhibited a low fatigue life due to hydrogen embrittlement. Hydrogen embrittlement induced crack initiations formed under the galvanizing layer and adversely affect fatigue life. It was observed that local embrittlement on the outer surface of the spring wire causes crack initiations and disperses through the pearlitic interlamellar microstructure. Compared to non-galvanized and shot-peened specimens with the same surface roughness, compression springs, galvanized compression springs exhibited a 25 % reaction force loss at 50 000 cycles.

Neuro-fuzzy fatigue life assessment using the wavelet-based multifractality parameters

This study aims to establish a fatigue life predictive model based on multifractality of road excitations using neuro-fuzzy method to assess the durability of suspension spring. Traditional durability analysis in time domain is complicated and time-consuming due to the needs of large data amount. Thus, it is an idea to adopt an adaptive neuro-fuzzy inference system (ANFIS) for relating the performance of coil spring to the multifractal properties of road excitations, giving a meaningful fatigue life prediction. Different membership function numbers were tested to obtain the optimum membership function number. During the data training process, the checking data was used to test the trained model each Epoch of training for overfitting detection. As a result, the Morrow-based fatigue life prediction model was found to give the most suitable result with three membership functions. The SWT-based model needed five membership functions due to nonlinear properties in the SWT-based fatigue life data. Training process of Morrow-based-ANFIS was stopped at Epoch 8 given its lowest checking root-mean-square-error of 0.6953. SWT-based model recorded a higher error of 0.7940. The neuro-fuzzy models gave accurate fatigue life predictions with 96 % of the data distributed within the acceptance boundary, hence, contributing to an acceptable assessment of coil spring fatigue life based on load multifractality. This study had shown a nonlinear relationship between road multifractality and durability performance of coil spring. Multifractality had been proven an important feature to characterise various road excitations for durability prediction.