Durability prediction of coil spring through multibody-dynamics-based strain generation

PurposeThis paper aims to assess the fatigue life characteristics of vehicle coil spring under random strain load in the time domain. Cyclic random road loads caused fatigue failure for automotive components during their operating condition. .Design/methodology/approachThe coil spring model is developed through finite element analysis software. The critical region and fatigue life cycle of coil spring is evaluated through finite element analysis. The experimental is set up to capture the random strain signal of the rural, highway and campus road. The sampling rate of the random strain signals data captured were 500 Hz in 150 s. Then, fatigue life is assessed through Goodman, Brown-Miller, Fatemi-Socie, Wang-Brown fatigue life models. Goodman model is evaluated through finite element analysis in order to compare with fatigue experimental results.FindingsThe fatigue life was estimated for Brown-Miller model is the highest (4.32E4, 4.10E4, and 3.73E4 cycles/block for rural, highway and campus respectively) followed by Goodman model, Brown-Miller, Fatemi-Socie and Wang-Brown models respectively. The conservative fatigue life 1:2 and 2:1 data scattering approach is proposed in order to determine the acceptability of the data.Originality/valueHence, the proposed fatigue life models can be used to assess multiaxial fatigue under random strain signals for the automobile coil spring.

In spite of the tough pitch copper material is used for the many kinds of conductors of electrical machining devices, the fatigue phenomenon of the tough pitch copper material does not still clarify under variable stresses considering to a service loading. Then, constant stress amplitude fatigue tests were carried out for the tough pitch copper sheet material and then the fatigue life under variable stresses were predicted by Miner's law using constant stress tests results as shown S-Ndiagram. The program fatigue tests consist of two steps and multifold stress levels were carried out for tough pitch copper sheet specimens compared with the fatigue lives predicted by using Miner's law. As it was clear that the fatigue lives predicted by using Miner's law were shorter than the experimental program fatigue lives under variable stresses in service loading, so new practical diagram modified from original S-N diagram was proposed. The fatigue lives predicted by using new S-N diagram coincide with experimental fatigue lives under variable stress consist of two or three step and multifold stress levels.

This paper presents the evaluation of the automobile coil-spring strain-displacement relationship for strain signals generation and fatigue life predictions. The development of a strain and spring vertical displacement relationship is significant because measuring vehicle wheel displacements and forces are complex and costly. Hence, there is a need to estimate the strain data using alternative measurement, such as vibration signals. In this analysis, strain and acceleration data were collected from a vehicle that has travelled on different road conditions. Through the material elastic strain energy and spring potential energy relationship, a coil-spring parameterise strain-displacement relationship has been developed and evaluated using a scatter band and correlation approach. Using this proposed model, the strain time histories were obtained based on acceleration data. For fatigue life analysis, most of the predicted fatigue life was distributed in the acceptable range using the scatter band approach where the data correlated at coefficient of determination value (R2) of 0.8788. With a suitable correlation value, this analysis proposed an alternative strain generation method for suspension coil spring fatigue life prediction, which could significantly shorten the spring development time.

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.

The need to generate realistic strain signals at an automotive coil spring for durability simulation leading to fatigue life assessment

In vehicle multi-body dynamics (MBD) modeling, the stiffness parameterization of leaf spring (LS) is an unavoidable challenge regardless of the selection of modeling methods. On the contrary, the parameterization of Coil Spring (CS) stiffness is easy to achieve by adjusting the scale factor. Therefore, a novel LS stiffness parameterization method by treating the suspension stiffness as an intermediate variable through a CS stiffness is proposed based on the virtual displacement theory. The proposed method is then implemented in the vehicle-level modeling of a commercial Van with front transverse leaf spring suspensions and rear longitudinal parabolic leaf spring suspensions. The MBD model is validated by natural frequency tests and suspension stiffness simulations. Furthermore, the vertical acceleration of the car body is also verified. Results show that the root mean square (RMS) values of body vertical acceleration in the equivalent CS model are just slightly lower than that in the LS suspensions. The applicability and capability of the proposed method are proven to address the limitation of LS stiffness parameterization in MBD modeling. It lays the groundwork for efficiently simulating the LS suspension in vehicle ride and handling design and optimization.

In the previous studies, prediction of fatigue life at the lower suspension arm is only done based on strain signals obtained on a straight road. Considering the main function of the lower suspension arm is to stabilize the vehicle when turning, the purpose of this study is to predict the fatigue life of the lower suspension arm when the vehicle goes straight and turns clockwise and counterclockwise. The three roads are passed by vehicles with a speed of 30 km/hour. Measurement of strain signals is done by attaching a strain gauge to the lower suspension arm on the left side of the vehicle. Based on the simulation results based on the strain-life approach the lowest fatigue life is given by turning clockwise direction with 2.56E+6 cycles so that it breaks using the Coffin-Manson model. This value is low than the age of fatigue life when the vehicle goes straight and turns counterclockwise, each with 5.85E+6 cycles so it breaks and 5.08E+7 cycles so it breaks. This value is also comparable to that produced by the Morrow and SWT models. When the vehicle turns right, the lower suspension arm on the left side receives a strain that is greater than when the vehicle turns left, which is 5%. Strain received by the lower suspension arm can shorten the fatigue life of the component. Turning roads shorten the fatigue life of lower suspension arm so that 44% compared to straight roads.

This study characterized the properties of random strain loading data for using power spectral density (PSD) in frequency domain of a heavy vehicle leaf spring. This is due to missing data caused by the sensitivity of the strain gauges in capturing strain signal. Strain signal was captured from a leaf spring component for 100 s at a sampling rate of 200 Hz using strain gauge. Fatigue life prediction was computed using strain-life models: Coffin-Manson, Morrow and Smith-Watson-Topper (SWT). The fatigue strain data showed that downhill data produces the lowest fatigue life prediction at 3.42 × 102 cycles/block with high energy of 3.6 × 104μɛ2.Hz-1; then it was followed by curve and highway data. This was supported by the root-mean-square (RMS) value at 324.24 μɛ as it is directly related towards the PSD based on the energy contained for each captured signal. The correlation of fatigue life and strain amplitude was calculated to identify the distribution of fatigue strain data of leaf spring. Thus, the fatigue strain loading data can be characterized properly based on the energy content in PSD, the statistical parameter in the form of RMS value and the correlation with strain amplitude for random strain loading of leaf spring.

Experimental and numerical investigation on fatigue performance of non-load-carrying fillet welded joints

A Walker-based mean strain correction model of low-cycle fatigue (LFC) life prediction is proposed for high loaded parts. The model is based on a function depending on the strain range and strain ratio controlled in the strain-controlled LCF test of fatigue specimens and a constant reflecting the material sensitivity to strain ratio. The independence from the stress cycle parameters which can change during the strain-controlled LCF test is an obvious advantage of the model. The model was verified using the results of strain-controlled LCF tests of smooth titanium alloy Ti-6A1-4V ELI and iron-based alloy specimens conducted at room temperature. The proposed model was compared to the Smith - Watson - Topper and Walker models that take into account the mean stress effect. The proposed model provided the best prediction accuracy for titanium alloy. For Iron-based alloys the results obtained by the Walker model and the model proposed are close to each other. A simplified model based on the analysis of model parameters tailing into account the mean strain effect for predicting fatigue life of aeroengine critical parts is developed using a limited amount of experimental data when only the results of Rε = 0 tests are known. A comparison of the predicted life with the number of cycles to failure showed satisfactory results of fatigue life prediction for Ti-6A1-4V ELI and Iron-based alloys specimens.

This paper presents a method for predicting fatigue failure using a virtual prototyping software tool that allows the simulation of real material behavior. Computer models are used to simulate the three dimensional microstructure in which fatigue evolves. Because grain structure properties are randomly distributed through any macro-sized structure, Monte Carlo simulation is used to give a probabilistic distribution of fatigue failure outcomes over the operating life of the structure. The reliability of structural elements with complex stress distributions is predicted by integrating the fatigue simulation model within traditional structural finite element models (FEM). The reliability analyses results for all the individual elements are combined using system reliability modeling techniques to determine the fatigue reliability of the entire component. This results in prediction of fatigue reliability as cycles to failure probability or the probability of exceeding a fatigue threshold. In making the fatigue reliability predictions, only the material micrographs, stress-strain curves and a single fatigue test data point (at a single stress) were provided. The results show excellent correlation between the predicted fatigue life and experimental fatigue life

In this study, we propose a novel cumulative-damage model based on continuum damage mechanics under situations where the mechanical components are subjected to variable loading. The equivalent completely reversed stress amplitude accounting for the effect of mean stress, stress gradients, loading history, and additional hardening behavior related to nonproportional loading paths on high-cycle fatigue under variable loading is elaborated. The effect of mean stress, stress gradients, loading history, and additional hardening behavior related to nonproportional loading paths is considered by averaging the superior limit of the intrinsic damage dissipation work in the critical domain. We developed a novel cumulative-damage model by introducing the equivalent completely reversed stress amplitude into the damage-evolution model. For better comparison, existing cumulative-damage models, including the Palmgren–Miner law, corrected Palmgren–Miner law, Morrow’s plastic work interaction rule, and Wang’s rule, were employed to predict the fatigue life under variable loading. The proposed model performed better, considering the error scatter band obtained by plotting the predicted and experimental fatigue life on the same coordinate system. The model precisely predicts fatigue life under variable loading and easily identifies its material constants.

A durability related analysis has been performed using a new statistical-based method, called the Hybrid Integrated Kurtosis-based Algorithm for Z-notch filter (Hybrid I-kaz) Technique. This method provides a two dimensional graphical representation of the signal amplitude and the Hybrid I-kaz coefficient that were used to measure the degree of data scattering. For validation purposes, road tests have been conducted in order to measure the strain and vibration signals on a coil spring. Three road surfaces were used for the road test and data collection purposes. This study used test signals which excited based on three different road surfaces. The 5-mm strain gauge and an accelerometer were fixed on the outer surface of the coil spring for measuring the variable amplitude strain loadings together with the vibration response. The time domain strain and vibration signals were then analysed using global signal statistics and Hybrid I-kaz coefficients. Finally, it was found that the respective coefficients for each signals showed an increment with the total value of strain range and vibration amplitudes.

Fatigue assessment of naval welded assemblies

The fatigue life evaluation of adhesively bonded joints has attracted more and more attention with its extensive application. Here, the fatigue experiments under various loading conditions were carried out to understand the stress amplitude, mean stress, cycle period, and loading path related to the fatigue life of the adhesively bonded tubular butt-joints. The experimental results showed that the fatigue life of the adhesively bonded butt-joint decreased with the increase of stress amplitude and mean stress, and the influence of cycle period on the fatigue life was more obvious since the mechanical property of the selected adhesive was rate dependent. Meanwhile, the fatigue life of the adhesively bonded butt-joint was influenced by the loading path under multiaxial loading conditions. In addition, the relationship between the damage parameters and fatigue life was characterized based on the experimental observations. Accordingly, a stress-based fatigue life prediction model was developed which can simultaneously consider multiple damage parameters related to fatigue life of the adhesively bonded joint. The predicted results indicated that the predicted life correlated well with the experimental data of the adhesively bonded joints.