Fatigue Analysis Tool Research Articles

Application of digital image correlation to derive Paris' law constants in granite specimens

This study investigates the effectiveness of Digital Image Correlation (DIC) as a powerful tool for deriving Paris' law constants in black granite specimens subjected to cyclic loading. A series of monotonic and cyclic loading tests on rectangular granite specimens yields valuable insights into geological material fatigue behavior, establishing monotonic tests as foundational references for subsequent cyclic loading experiments. Innovative DIC software application enables precise tracking and analysis of Crack Mouth Opening Displacement (CMOD) values, revealing distinct, observable patterns in crack growth during cyclic loading. A notable contribution lies in the implementation of a compliance calibration technique integrating Finite Element Method (FEM), facilitating the direct linkage between CMOD values and effective crack lengths, resulting in highly accurate Paris' law constants. With an average of 1.04 E −7 for C and 8.95 for m, these constants are essential for predicting fatigue crack propagation in granite specimens. This research underscores DIC's efficacy as a pivotal fatigue analysis tool, enhancing predictive capabilities for structural safety and durability assessments in geological materials, while emphasizing the crucial role of advanced imaging and numerical techniques in material science and structural engineering. It lays a robust foundation for future geological material studies and comprehensive structural integrity assessments.

A probabilistic framework for fatigue damage of lift based wave energy converters

Wave cycloidal rotors are lift based wave energy devices that have shown great potential to harness the energy of the waves through the use of submerged hydrofoils. Although the lift force of the foils can be controlled passively or actively to maximise power extraction, the foils of the rotor are subject to variable loading which can expose these components to premature mechanical failure. Therefore, it is important to develop novel fatigue analysis tools that help predicting the lifetime of this type of lift based devices. In this paper, we test the hypothesis that when cyclorotor operates at constant rotational velocity in irregular waves, the fatigue damage of the hydrofoil stress hot spot can be computed through a probabilistic approach. We compare our results to the fatigue damage computed with well established deterministic methods. We find that for both narrow and broad band stress energy spectra, the probabilistic method works well at high probability sea states, when the range of stresses does not exceed the inflection point of a double slope SN curve. This is a promising outlook since it confirms that the fatigue damage of these versatile lift based wave devices can be treated in a similar fashion to the fatigue damage of conventional offshore structures.

Design & Optimization Gudgeon Pin for C.I. Engine

Abstract: Premature wear of the Gudgeon pin is the major concern for the company. Gudgeon pin connects the piston and the small end of the connecting rod of IC engines. This paper deals with Stress analysis and Fatigue analysis of Gudgeon pin used in diesel engine. In stress analysis frictional stresses and von-Mises stresses coming on Pin are determined using finite element analysis tool ANSYS 16. Effect of different factors on frictional stresses and Von-Mises stresses such as change in internal diameter of pin and application of diamond-like carbon (DLC) coating are analyzed. In Fatigue analysis, fatigue life of Pin is determined using fatigue analysis tool FEMFAT 5.0 b. Effect of change in surface roughness of connecting rod small end bush and change in internal diameter of pin on fatigue life is analyzed.

A general life estimation method for overhead conductors based on fretting fatigue behavior of wires

This work proposes a new methodology to assess the fatigue life of overhead conductors. The approach relies on (i) a global stress analysis of a multistranded conductor using a 3D finite element (FE) beam-to-beam contact model and (ii) a local fatigue damage analysis of the wires that exploits the similitude concept of the S-N method. The methodology can be applied to general conductor-clamp assemblies and provide predictions about the fatigue life and the critical regions of failure of conductors. The effectiveness of the methodology is demonstrated using experimental data of an AAAC 900 MCM conductor obtained in a resonant fatigue testing bench. Different levels of tension loads and bending displacement amplitudes were considered in the assessment. Experimental strain measurements show that the conductor-clamp FE model can compute the stress distribution along the critical region of failure of the conductor with satisfactory accuracy. New fretting fatigue data together with literature data of AA6201-T81 wires are used to demonstrate that the stress-based version of the Smith–Watson–Topper model can reasonably describe the fatigue behavior of these aluminum wires and hence is used as fatigue parameter to predict the fatigue behavior of the AAAC 900 MCM. The predicted critical regions of failure and fatigue lives of the conductor-clamp assembly were in good agreement with the experimental observations. The level of accuracy obtained is acceptable for engineering calculations, indicating that the methodology can be a promising fatigue analysis tool for overhead conductors.

Lessons from a fatigue prediction challenge for an aircraft wing shear tie post

Like many aircraft operators and maintainers, the Royal Australia Air Force requires the most robust of metal fatigue analysis tools for both informed acquisition and cost effective sustainment of aircraft. The Defence Science and Technology Group has been investigating and enhancing metal fatigue predictive tools for many years. This paper describes a local blind-prediction challenge for a series of coupons manufactured from Aluminium Alloy 7050-T7451 plate simulating a combat aircraft wing root shear restraint (or shear tie post) subject to a combined aerodynamic buffet and manoeuvre load spectrum. Analysts were provided with details including the geometry, material and loading, and were asked to predict the total fatigue life. Results from a detailed three dimensional finite element model of a cracked or uncracked test coupon were also available to the analysts. The results from two separate, independent blind predictions are presented and assessed along with further non-blind analyses to evaluate the current capabilities. The exercise found that accurate and reliable predictions are possible in a case like this, but the results are dependent on the availability of high-fidelity short crack rate data and a suitable stress intensity Beta solution. The work will provide confidence in existing fatigue life modelling capabilities leading to improvements in safety, availability and cost reduction.

A Rapid Fatigue Analysis Method of Aluminum Honeycomb Structure with Defects Based on Static Test and Numerical Simulation

At present, most of the substrates of the multifunctional components are honeycomb sandwich structures. Therefore, the study on the fatigue characteristics of honeycomb sandwich structures with defects is helpful to accelerate the engineering application process of the multifunctional structures.In order to study the fatigue characteristics of multi-functional structure under three conditions of tension, compression and three-point bending, the author of this paper proposes a rapid fatigue analysis method of based on statics experiment and numerical simulation.Firstly, the static experiments of the structure under three mechanical conditions of tension, compression and three-point bending are carried out, and then the static simulation is carried out with ANSYS software under the same conditions, and the finite element model in ANSYS is modified according to the experimental results. Finally, the fatigue of the aluminum honeycomb sandwich structure with defects under three conditions is calculated quickly by the fatigue analysis tool in ANSYS The analytical expression between the fatigue life and the load level of the structure under different load ratios is obtained by using the least square method.The fatigue analysis method avoids the complicated fatigue experiments, solves the problem of obtaining the fatigue characteristics of the honeycomb sandwich structure with defects at low cost and high speed under different mechanical conditions and greatly improves the analysis efficiency of the fatigue characteristics of the complex structure.

A cloud-based fatigue analysis tool with interactive Neuber’s master curve

A cloud-based fatigue analysis and life prediction tool is presented. Users around the globe may access it via Internet by means of multiple platforms such as desktop and laptop computers, tablets and/or smart-phones. It is an intuitive educational software, aimed also to assist designers in the pre-prototyping stage in fatigue life estimation for smooth or notched parts subjected to constant amplitude, block loading, and spectrum loading histories. For spectrum amplitude loading a dedicated spectrum software package is provided, which is essential for a potential clean-up and/or desired modifications of a raw spectrum data. Subsequently, a rainflow method is utilized and the corresponding hysteresis loops at the notch-root or critical “hot spot” location are determined and plotted. For notched components, an interactive Neuber’s master curve is utilized and discussed. It is shown, that the Neubers’s master curve is only material dependent and is applicable for both monotonic and cyclic loading situations.

Improvement of an Exponential Cohesive Zone Model for Fatigue Analysis

Cohesive zone model is an important tool for fatigue analysis, especially for fatigue crack growth along with an interface. A pioneering model is the one of Roe and Siegmund (Eng Fract Mech 70:209–232, 2003), in which the damage accumulation is calculated using an irreversible exponential cohesive law. However, it is found in our recent research that the constant unloading and reloading slope in Roe’s damage evolution law could cause a discontinuity in the traction–separation curve when the mixed mode ratio changes. This limits its application to single mode cyclic loading or scenarios where the mixed mode ratio is constant. In this paper, the cause of such discontinuity is analyzed, and a robust cyclic loading formulation is proposed, which will help the exponential cohesive law remain continuous under arbitrary mixed mode cyclic loading. Moreover, it is found in this paper that by adding a scale factor to the Roe’s damage law, the fatigue failure time can be approximated with less computational cost. The relationship between fatigue failure time and the scale factor is shown to be inversely proportional.

Customization of Open-Source CFD Code to Predict the Weld Shape and Determination of the Optimal Welding Method using a Simple Fatigue Analysis Tool

溶接シミュレーション技術は自動車や建設機械メーカーを中心に活用が進んでおり、安全性に関わる重要保安部品に生じる熱変形や残留応力、疲労寿命を設計段階で予測し、対策を講じるためのツールとして活用されている[1]．本稿では、筆者らが取り組んできた溶接残留応力と疲労寿命の予測技術について紹介する．

An Interactive Web-based Tool for Fatigue Analysis and Life Prediction

This paper presents an interactive web-based tool for fatigue analysis and life prediction methodology of smooth and notched components. Users around the globe may access it via Internet by means of multiple platforms such as desktop and laptop computers, tablets and/or smart-phones. In particular, the users with a limited fatigue background would benefit from “on-the-fly” fatigue learning experience. It makes a self-explanatory and frustration free web-based education software, which allows users to learn the fatigue fundamentals while expanding their knowledge on modern fatigue analysis methods. The tool is aimed to assist a designer in fatigue analysis and file predictions of parts subjected to constant amplitude, block loading, and variable loading histories. For variable amplitude loading a dedicated spectrum software package is provided, which is essential for a potential clean-up and/or desired modifications of a raw spectrum data. Subsequently, a rainflow method is utilized and the corresponding hysteresis loops at the notch-root or critical location are determined and plotted. In analyses, three convenient and innovative “master curves” techniques are used, namely for Neuber's rule and also for stress- and strain-based fatigue life approaches.

An Interactive Online Notch Fatigue Analysis Tool

This document presents an interactive tool for notch fatigue analysis and life prediction. Modified Neuber’s rule is used to determine notch-root elastic-plastic stress and strain. The effect of mean stress on fatigue crack initiation life is accounted by utilizing a deviatoric formulation of the Smith-Watson-Topper parameter. For variable amplitude loading a rainflow method is used and the corresponding hysteresis loops at the notch-root are determined. Then, the relevant interactive graphs and calculated values are displayed. The propose methodology is intended to be a comprehensive fatigue analysis tool used by any designer engineer in global market environment. A brief flow chart of the intended tool is presented here.

Development of CGAP for Fatigue Damage and Crack Growth Analysis: Verification, Validation and Examples of Application

A computer program for fatigue life and crack growth analysis, entitled CGAP, has been developed at the Defence Science and Technology Organisation in support of the aircraft structural life assessment programs of the Australian Defence Force. The key objectives in developing this software platform were to provide a flexible, robust, economical, adaptable, and well verified and validated fatigue analysis tool. CGAP provides advanced capabilities for crack growth analyses, including crack growth in notch-affected plastic zones, and for probabilistic crack growth analyses. It also provides seamless interface to third-party models, such as FASTRAN and FAMS, enabling easy benchmarking against and collaborating with international partners. This paper summarises some of the recent developments in analytical and numerical fatigue damage and crack growth modelling, with emphasis on software verification and validation. Examples will be presented to illustrate its application.

Simplified Viscoelastic Continuum Damage Model as Platform for Asphalt Concrete Fatigue Analysis

Cracking in asphalt concrete pavements is a major form of pavement distress in the United States. Because the cracking phenomenon is complex and cracking is often affected by both material and structural factors, field engineers have no quick and effective test and analysis protocols. A suite of fatigue analysis tools—as well as applications built around the simplified viscoelastic continuum damage (S-VECD) model—is presented. The S-VECD formulation is presented in a summarized form. Next, the characterization protocols, which are consistent with the capabilities of the asphalt mixture performance tester, are shown. Considerable attention is then given to S-VECD–based analysis tools for assessment of material- and pavement-level fatigue performance. Results show that the S-VECD model can be used to predict the number of cycles until fatigue failure for both constant stress and constant strain loading. The S-VECD model's sensitivity to mixture composition and external factors is shown through predictions of the endurance limit. Finally, pavement performance predictions are used to show how the S-VECD model can predict the field performance results of full-scale accelerated pavement tests, quantify the expected performance of pavement design alternatives, and identify factors that affect top-down cracking.

Flexural fatigue analysis of a CFRP form reinforced concrete bridge deck

Concrete bridge decks reinforced with fiber reinforced polymer (FRP) composite panels have recently been used where the FRP panels also serve as the permanent formwork for concrete. Comparing to their short-term behavior, their long-term performance especially under repeated traffic loads (fatigue) has not yet been widely known. This paper presents a fatigue analysis tool developed for a new steel-free concrete bridge deck reinforced with carbon FRP stay-in-place form. The developed model takes into account the cyclic creep of concrete in compression, the reduction in flexural stiffness due to fatigue tensile cracking and the reduction in modulus of rupture under cyclic loading. Comparisons with experimental data show reasonable agreement where a full-size 2-span deck specimen was subjected to millions of fatigue cycles. The parametric study recommends reducing the amount of FRP reinforcement and concrete strength of the current design, and lower loading rate may introduce more stiffness degradation in the system.

Integrated physics-based approach for the reliability prediction of thermal systems

A broad reliability prediction method that can deal with complex thermo-fluidic systems is introduced. The procedure provides an engineering tool by integrating multiple computational packages that enable the simulation of a wide array of systems, especially those involving physics interactions such as fluid flow and solid medium. Computational Fluid Dynamics, Finite Element Method, Monte Carlo Simulation and fatigue analysis tools are integrated within this physics-based reliability prediction approach. The complete procedure is demonstrated using a simple example, and then validated using boiler pipes experimental data. CFD simulations are used to determine the convective terms necessary for the transient FEM thermal analysis. The thermal analysis provides maximum thermal stress whereby the fatigue life of the component is evaluated. As a result of input parameters uncertainty, the expected life will be in the form of a Probability Density Function, which enables the calculation of the reliability of the component.

A fast, versatile fatigue post-processor and criteria evaluation

This paper is concerned with the development and use of a general High Cycle Fatigue (HCF) post-processor, FAST, Fatigue AnalysiS Tool. It is used to evaluate and develop HCF criteria. FAST can handle many kinds of criteria and evaluate them with fatigue test results from both standard test specimens and actual components. When a reliable criterion exists, FAST will be used for design purposes. The principles of FAST are outlined and an example is given where seven local multiaxial stress based criteria are evaluated, along with the commercial fatigue post-processor Femfat. The conclusion is that a correct treatment of the volume or stress gradient effect is more important than the choice of criterion.

Crack Initiation, Propagation, and Arrest in 316L Model Pipe Components under Thermal Fatigue

Abstract There is a continuing need for reliable thermal fatigue analysis tools to ensure that high safety levels are maintained in the main coolant lines of light water reactors. As a contribution to this effort, a combined experimental and numerical investigation has been conducted on cylindrical components of 316L stainless steel subjected to cyclic thermal shocks of varying intensity. It exploits a dedicated rig in which the tubular test pieces are subjected to induction heating and water quenching. Under the applied loading, a network of cracks initiates at the inner surface; some of these propagate further through the wall thickness. The number of cycles to crack initiation is estimated from surface replicas taken during intermittent stops, whereas the crack depth of fatigue cracks is measured using an ultrasound time of flight diffraction technique (TOFD). The analysis is done by a sequentially coupled thermal-stress finite element analysis using a cyclic plasticity model. Predictions of the crack initiation life (based on crack initiation curves as well as crack propagation models for microstructurally short cracks) are in good agreement with the test results. Crack propagation for small fatigue cracks was estimated by plastic strain amplitude based propagation formulas, whereas long crack propagation is analyzed by Paris law type criteria using ΔK as well as ΔCTOD.