PurposeFor 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.Design/methodology/approachThis 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.FindingsAccording 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.Originality/valueThe 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.
PurposeAiming at the problems of poor accuracy and limitation in strength assessment of spot welding vehicle body caused by uncertain factors, such as key component size and nugget diameter, the numerical models of strength uncertainty analysis of spot-welded joints were constructed based on evidence theory and fuzzy theory.Design/methodology/approachEvidence theory and fuzzy theory are used to deal with the uncertainty of design parameter, and differential evolution algorithms are used to calculate the propagation process of uncertainty in this model. Furthermore, efficient relationship between the strength of welded joints and each design parameter is constructed by using response surface proxy model, which effectively avoids the problem of repeated complex finite element analysis in uncertainty analysis.FindingsThe results show that the constructed uncertainty numerical model is effective for the multiple uncertainties and give interval results under different probabilities and affiliations, which can more effectively evaluate the strength of the welded body structure to avoid overly conservative estimates for deterministic design.Originality/valueThe evidence theory is improved and combined with differential evolution algorithm and response surface method to effectively improve the computational efficiency. Based on the improved evidence theory and fuzzy algorithm, the numerical models for the uncertainty analysis of solder joint strength of welded structures are constructed and their feasibility is verified.
It is important for the study of circuit breaker opening capacity to know how to accurately measure the movement characteristics of the actuator. In order to measure the motion characteristics of the actuator accurately, an image processing method based on LabVIEW platform is proposed in this paper to build a system for detecting the motion speed of the actuator. In this paper, a high-speed camera is used to capture the motion images of the circuit breaker during the opening process, and the VISION module in LabVIEW is used to locate the motion edges with high accuracy, calculate the motion parameters of the moving end during the motion process, and evaluate the opening capacity of the circuit breaker by combining the motion parameters. The experimental results show that the proposed method can achieve accurate detection of the motion parameters of the operating mechanism, and has the advantages of high accuracy and simple operation, which can provide strong technical support for the study of the breaking capacity of the circuit breaker.
The movement speed of the operating mechanism is one of the main factors affecting the breaking performance of the circuit breaker. To accurately detect the movement speed, this paper proposes an image processing method based on LabVIEW virtual instrument and designs a set of software and hardware systems for real-time movement speed detection of the operating mechanism. On the basis of the movement images of the operating mechanism collected by the high-speed camera, it uses the image processing module in LabVIEW to pre-process the images. The paper adopts the Laplacian edge detection operators to detect the edges and extract the edge feature information for straight line fitting and data processing. The experimental results show that the detection system can effectively detect the motion state of the operating mechanism, realize the real-time detection of the motion state of the operating mechanism, and provide technical support for the detection of the motion characteristics of the circuit breaker.
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