Search results

Failure of a critical reinforced concrete beam due to fatigue can have severe safety and production consequences, and preventative repair/replacement of such a beam is expensive. It would therefore be beneficial if repair/replacement can be done based on an accurately and conservatively predicted remaining useful life (RUL). The purpose of this paper is to develop such a model.

Condition-based maintenance is a maintenance approach that uses empirical/analytical models and a measurable condition to predict remaining useful life. The P-F curve (condition-life) is a useful tool that can aid in making these decisions. A model to create a P-F curve is developed using rebar fatigue test results (in the form of an S–N curve) and the Palmgren-Miner law of damage accumulation. A Monte Carlo simulation with statistical distributions is employed to provide confidence levels of RUL outputs.

An example of how the model can successfully be used in practice is shown in this paper, and a sensitivity study is performed leading to conclusions being drawn with regard to damage tolerant design considerations.

If a critical reinforced concrete beam fails due to fatigue can have serious consequences. This paper develops a model to help base repair/replacement decisions based on accurately and conservatively predicted RUL. Financial and safety benefits would be gained if this model would be used in practice.

This paper aims to study and modify the notch equivalent stress method, as well as to establish the notch equivalent stress range S–N curve and apply it to the fatigue assessment of engineering examples.

This paper studies the notch equivalent stress method and puts forward the concept of “singular equivalent crack”. Combined with the fatigue test results, by proposing to consider the singular coefficient of the transition angle of the welded structure and the introduction of material correction factors, this paper derives the notch equivalent stress equation for commonly used welded joints applicable to steel, and finally establishes the notch equivalent stress range of the S–N curve.

The obtained results show that the dispersion of fatigue data is 65.6 and 75.4% for T-joints and transverse cross-joints, respectively, under S–N curves using notched equivalent stress compared to the nominal stress range. The fatigue evaluation error of the modified notch equivalent stress equation for transverse cross welded joints improved by 50.65%, 53.1 and 39.6% on average, respectively, compared to the original other methods. The fatigue evaluation error for T-joints improved by 13.4 and 13.9%, respectively, compared to the original other methods.

There are relatively few studies on the fatigue assessment of notch equivalent stress method. In this paper, the notch equivalent stress method is studied and modified to improve the accuracy of fatigue assessment of welded structures with singular stresses.

For the difference of the change law of material memory performance and the influence of damage state on memory performance, this paper aims to establish a general model of fatigue damage accumulation based on dynamic residual S–N curve and material memory characteristics.

This paper introduces the material memory characteristics, combined with the residual S–N curve method, and uses the exponential decay function of the load cycle to construct the material memory performance function. While considering the damage state, the loading order can be fully considered. The parameter d in the function not only represents the variation of the material's memory property, but also considers the influence of the damage state.

According to the test data of welding joints of common materials, alloy materials and other materials, the validity and feasibility of the fatigue cumulative damage model constructed were verified. The numerical results show that under the grading load, the fatigue cumulative damage model can be used to predict the fatigue life of welded structures and has high prediction accuracy and more approximate to the actual experiment results. It can be directly applied to the fatigue life prediction and design of actual engineering welded structures.

The model not only considers the effect of damage state and loading order on damage accumulation, but also contains only one material parameter, which is easy to obtain. The prediction accuracy and engineering practicability of fatigue were significantly improved.

Fastener technology is one of the key technologies of the ballastless track structure, and the spring strip is the key component to realize the fastener function. Based on the fatigue test of the WJ-7 type fastener of the ballastless track in China, it is concluded that the fatigue damage of an elastic strip is the main reason for the decline of service performance of the fastener. The purpose of this paper is to discuss the fatigue life of the fastener.

First, a DH3818 static strain tester is used to measure the static strain signal in the elastic strip fatigue test, and then the fatigue limit of the WJ-7 elastic strip is calculated. Finally, the fatigue life of the fastener strip is estimated.

The findings of the paper are as follows: first, the lowest fatigue life with a survival rate of 99 percent should be taken as a reference for the service times of WJ-7; second, the fatigue life of the modified formula found to be short under the same stress amplitude.

The fatigue test is processed by the authors and the results of elastic strip are obtained based on the test. Meanwhile, the corresponding limit value of the fatigue stress amplitude is calculated based on the tested results.

The purpose of this paper is to determine the ultra-high cycle fatigue behavior and ultra-slow crack propagation behavior of selective laser melting (SLM) AlSi7Mg alloy under as-built conditions.

Constant amplitude and two-step variable amplitude fatigue tests were carried out using ultrasonic fatigue equipment. The fracture surface of the failure specimen was quantitatively analyzed by scanning electron microscope (SEM).

The results show that the competition of surface and interior crack initiation modes leads to a duplex S–N curve. Both manufacturing defects (such as the lack of fusion) and inclusions can act as initially fatal fatigue microcracks, and the fatigue sensitivity level decreases with the location, size and type of the maximum defects.

The research results play a certain role in understanding the ultra-high cycle fatigue behavior of additive manufacturing aluminum alloys. It can provide reference for improving the process parameters of SLM technology.

Friction stir welding lap joints of aluminum alloy AA6082-T6 were joined using two distinct configurations. The purpose of this paper is to study the effect of the welding line direction on the fatigue life of the specimens. For that purpose, specimens with the welding line parallel to the loading direction and with the welding line perpendicular to the loading direction were designed and manufactured. Fatigue tests were performed under constant amplitude load and stress ratio of R=0.1. As shown in previous studies, the hook defect plays a decisive role in the mechanical behavior of the joint, in particular when submitted to fatigue. The specimen geometry with the welding line parallel to the loading direction showed a superior fatigue behavior: for a given number of cycles to rupture, the level of stress is approximately twice as high as for the perpendicular configuration.

Two finite element models were created in order to study the behavior of the welded zone and, in particular, to compare influence of the hook defect in both configurations.

The specimen geometry with the welding line parallel to the loading direction showed a superior fatigue behavior: for a given number of cycles to rupture, the level of stress is approximately twice as high as for the perpendicular configuration.

The main objective of this work is to study the effect of the welding line direction on the fatigue life of the specimens. For that purpose, specimens with the welding line parallel to the loading direction and with the welding line perpendicular to the loading direction were designed and manufactured. Fatigue tests were performed under constant amplitude load and stress ratio of R=0.1. As shown in previous studies, the hook defect plays a decisive role in the mechanical behavior of the joint, in particular when submitted to fatigue.

The purpose of this paper is to propose the new dependences of cycles to failure for a given initial crack length upon the stress amplitude in the linear fracture approach. The anticipated unified propagation function describes the infinitesimal crack-length growths per increasing number of load cycles, supposing that the load ratio remains constant over the load history. Two unification functions with different number of fitting parameters are proposed. On one hand, the closed-form analytical solutions facilitate the universal fitting of the constants of the fatigue law over all stages of fatigue. On the other hand, the closed-form solution eases the application of the fatigue law, because the solution of nonlinear differential equation turns out to be dispensable. The main advantage of the proposed functions is the possibility of having closed-form analytical solutions for the unified crack growth law. Moreover, the mean stress dependence is the immediate consequence of the proposed law. The corresponding formulas for crack length over the number of cycles are derived.

In this paper, the method of representation of crack propagation functions through appropriate elementary functions is employed. The choice of the elementary functions is motivated by the phenomenological data and covers a broad region of possible parameters. With the introduced crack propagation functions, differential equations describing the crack propagation are solved rigorously.

The resulting closed-form solutions allow the evaluation of crack propagation histories on one hand, and the effects of stress ratio on crack propagation on the other hand. The explicit formulas for crack length over the number of cycles are derived.

In this paper, linear fracture mechanics approach is assumed.

Shortening of evaluation time for fatigue crack growth. Simplification of the computer codes due to the elimination of solution of differential equation. Standardization of experiments for crack growth.

This paper introduces the closed-form analytical expression for crack length over number of cycles. The new function that expresses the damage growth per cycle is also introduced. This function allows closed-form analytical solution for crack length. The solution expresses the number of cycles to failure as the function of the initial size of the crack and eliminates the solution of the nonlinear ordinary differential equation of the first order. The different common expressions, which account for the influence of the stress ratio, are immediately applicable.

This is the final part of the article by Gerhard H. Junker of the European Research and Engineering Standard Pressed Steel Co, Unbrako. Previous parts have covered mechanism of self loosening, design to prevent self‐loosening and test methods.

The purpose of this paper is to establish a law on the durability of thick aluminium wire bonds in low cycle fatigue for different geometries and wire diameters under a purely mechanical load.

Bond wires with different geometries were tested with various loads and a mechanical test bench, and their endurance was determined. The same load situation was modelled with finite element analysis and then compared against the experimental results.

A correlation was found between the plastic strain per cycle and the determined lifespan. Therefore, the lifespan can be calculated by mechanical‐plastic simulation for various loop geometries and loading cases.

The loop height strongly influences the durability of the wire bond, whereas other parameters, such as the loop angle, have a weaker influence on the bond heel lifetime.

The mechanical simulation is able to replace the time‐consuming lifetime experiments.

The Cryofit Fitting System achieves its novel abilities from a property called “shape memory”. Materials that have this property become weaker and more malleable when cooled below a certain critical temperature. In this state, they can be deformed easily and will remain deformed and relatively weak as long as they are kept below the critical temperature. When warmed above that temperature, they regain their original strength and return to their original shape with tremendous force.