Fatigue assessment of naval welded assemblies

Neural networks (NN) have been widely used in application of fatigue life prediction. In the use of fatigue life prediction for polymeric-base composite, development of NN model is necessary with respect to the limited fatigue data and applicable to be used to predict the fatigue life under varying stress amplitudes in the different stress ratios. In the present paper, Multilayer-Perceptrons (MLP) model of neural network is developed, and Genetic Algorithm was employed to optimize the respective weights of NN for prediction of polymeric-base composite materials under variable amplitude loading. From the simulation result obtained with two different composite systems, named E-glass fabrics/epoxy (layups [(±45)/(0)2]S), and E-glass/polyester (layups [90/0/±45/0]S), NN model were trained with fatigue data from two different stress ratios, which represent limited fatigue data, can be used to predict another four and seven stress ratios respectively, with high accuracy of fatigue life prediction. The accuracy of NN prediction were quantified with the small value of mean square error (MSE). When using 33% from the total fatigue data for training, the NN model able to produce high accuracy for all stress ratios. When using less fatigue data during training (22% from the total fatigue data), the NN model still able to produce high coefficient of determination between the prediction result compared with obtained by experiment.

RETRACTED: Fatigue property study and life assessment of composite girders with two corrugated steel webs

Short Fiber Reinforced Composite (SFRC) structures exhibit multiple microstructures (due to material flow during the process). They are generally subjected to variable amplitude loadings. In this context, a robust model is needed to predict fatigue life as a function of microstructure. In this paper, we propose a predictive micromechanical damage-based model allowing fatigue life prediction in the case of SFRC submitted to variable amplitude cyclic loading. An experimental study was firstly performed on Sheet Molding Compound (SMC) composite involving different microstructure configurations. Specimens were subjected to stress-controlled block loading. The influence of the order of the sequences was evaluated through Low-High amplitude (L-H) and High-Low amplitude (H-L) schemes. Damage accumulation is computed at the local scale to describe the evolution of the fiber-matrix interface damage until failure. A local failure criterion based on a critical damage state allowed predicting variable amplitude fatigue life as a function of microstructure. A good correlation was found between experimental and numerical results. Once the approach was validated, it has been used to model different useful variable amplitude loading schemes to emphasize the role of the loading sequence parameters and order.

Investigation of the fatigue behaviour of the welded joints treated by TIG dressing and ultrasonic peening under variable-amplitude load

PurposeEngineering components/structures are usually subjected to complex and variable loads, which result in random multiaxial stress/strain states. However, fatigue analysis methods under constant loads cannot be directly applied to fatigue life prediction analysis under random loads. Therefore, the purpose of this study is how to effectively evaluate fatigue life under multiaxial random loading.Design/methodology/approachFirst, the average phase difference is characterized as the ratio of the number of shear strain cycles to the number of normal strain cycles, and the new non-proportional additional hardening factor is proposed. Then, the determined random typical load spectrum is processed into a simple variable amplitude load spectrum, and the damage in each plane is calculated according to the multiaxial fatigue life prediction model and Miner theory. Meanwhile, the cumulative damage can be calculated separately by projection method. Finally, the maximum projected cumulative damage plane is defined as the critical plane of multiaxial random fatigue.FindingsThe fatigue life prediction capability of the method is verified based on test data of TC4 titanium alloy under random multiaxial loading. Most of the predicting results are within double scatter bands.Originality/valueThe objective of this study is to provide a reference for the determination of critical plane and non-proportional additional hardening factor under multiaxial random loading, and to promote the development of multiaxial fatigue from experimental studies to practical engineering applications.

Ultrasonic impact treatment (UIT), which is a type of peening method, is usually used as a post-weld treatment for mild steel in order to improve the fatigue strength of its welded joints. As there is insufficient fatigue data available on welded joints of austenitic stainless steel treated by UIT, the authors decide to conduct fatigue tests on butt welded joints of austenitic stainless steel treated by UIT. The results were compared with the fatigue lives of as-weld joints to investigate the effect of UIT on the fatigue lives of welded joints of austenitic stainless steel. The fatigue lives of butt welded joints treated by UIT were more than 1.5 times longer than those of as-weld joints. The following were considered as possible reasons for this improvement in fatigue life: change in residual stress near the weld toes, relaxation of stress concentration at the weld toes, and refinement of grains under the weld toes. The residual stress measured near the weld toes by using the X-ray diffraction method was transformed from tension to compression by the application of UIT. The stress concentration factors at the welded toes were reduced about 10% by the application of UIT.

Fatigue life prediction of parabolic leaf spring under various road conditions

Lightweight-structural durability design by consideration of variable amplitude loading

Study on fatigue damage laws and life prediction of CRTS-II ballastless track slab

Fatigue reliability assessment of ageing railway truss bridges: Rationality of probabilistic stress-life approach

<div class="section abstract"><div class="htmlview paragraph">Tractors, as agricultural machines consisting of various interconnected assemblies, work in unison to perform specific functions and achieve desired outputs. Among these assemblies, the Hood Assembly, Firewall Assembly, Scuttle Assembly, Fuel Tank Assembly, Fender Assembly, Floor Panel Assembly, and Footstep Assembly are all produced through sheet metal fabrication. The components of these assembly are made from sheet metal and are joined together using various techniques, such as bolts, welds, and others.</div><div class="htmlview paragraph">The inherent characteristics of welding processes generally results in welded joints having lower fatigue strength compared to the individual parts being joined. Moreover, welds are commonly applied at geometric features or areas where the section changes within a structure. As a result, even in a structurally sound design, welded joints are often more vulnerable to fatigue failure. Hence, a comprehensive assessment of the durability of a welded structure requires placing considerable emphasis on a thorough fatigue evaluation of the welded joints.</div><div class="htmlview paragraph">Since industrialization, extensive research has been conducted on fatigue analysis of welded joints, leading to the development of various standards. Widely used standards in the industry include Eurocode 3, BS7608,among others.</div><div class="htmlview paragraph">In this paper, British Standard BS7608 and "Volvo Method," which are widely used for fatigue life prediction of thin sheet metal welded components are discussed. BS7608, which is based on the structural hot spot stress approach, determines stress by extrapolating it from the components to the weld toe, while excluding stresses from areas close enough to the weld toe that could be affected by the weld toe geometry. The "Volvo Method," developed at Chalmers University in collaboration with Volvo Car Corporation, calculates structural stresses at the weld toe using finite element-based nodal forces and moments along the weld line, along with an analytical expression for the stress at the weld toe. The fatigue life of welds in tractor sheet-metal assemblies is predicted using both methods. Testing of the assemblies is conducted in an NABL-accredited laboratory. A strong correlation between the predicted fatigue life and the results from laboratory testing is established and presented in this paper.</div></div>

It has been shown in several studies that methods to improve the fatigue strength of welded structures, such as high-frequency impact treatment (HFMI), can increase the fatigue life of welded joints [1–6]. The results of these investigations led to current guidelines and recommendations for the fatigue assessment of HFMI-treated welded joints. Nevertheless, in practice, there are reservations regarding the efficiency of HFMI-treated welded steel joints under variable amplitude loading. Recent results [7] from studies on transverse attachments of the material S355 and S700 under variable amplitude loading show that the fatigue strength increasing effect of the HFMI-treatment is maintained compared to the as-welded state. The aim of this study is to analyse the sequence effect on the fatigue strength of HFMI-treated transverse attachments and to validate the applicability of linear damage accumulation hypotheses for the design of as-welded and HFMI-treated welded details. In this paper, fatigue test results with random variable amplitude loading (VAL) and high-low VAL and low–high VAL with linear spectrum for the two states as-welded (AW) and HFMI-treated joints will be presented.

Most mechanical and structural components are typically subjected to variable amplitude loading during their entire life. For practical purpose, it is computationally advantageous to approximate the load sequence by blocks of cycles with constant amplitude and stress ratio. But the indispensable influence on life evaluation of the correlation characteristics between individual load processes can be ignored in many cases. The paper first reviews the historical achievements on the equivalence disposal and life-prediction models applied for variable amplitude loading. Based on the idea of Gaussian copula type model, the fatigue life process can be discretized into blocks. The dependence character is described with correlation length. Then an ameliorated model based on Corten-Dolan accumulated damage rule is introduced to draw to the equivalent stress range. Using the disposed stress sequence, a life estimation algorithm based on damage mechanics is presented, during which the coupling between damage field and stress field is considered to deduce the damage evolution equation. Finally, the strategy discussed above is applied examplarily to a practical case.

Variable Amplitude Fatigue Life in VHCF and Probabilistic Life Predictions

A phenomenological stress–strain model for wrought magnesium alloys under elastoplastic strain-controlled variable amplitude loading