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Numerical and experimental investigations on Mannesmann effect of nickel‑based superalloy

Zhang Zhe, Liu Dong, Man Tongchi, Li Nan, Yang Yanhui, Pang Yuhua, Wang Jianguo

Archives of Civil and Mechanical Engineering

2022

Vol. 22, no. 3

art. no. e133

The preparation of nickel-based superalloy tubes by rotary tube piercing (RTP) process is still difficult due to the Mannesmann effect (central cracking phenomenon) has not been clarified. The combinations of numerical analysis and experiment verifications method were adopted in the study. The critical parameters for central cracking were determined by experiments. It was found that the evolution process of central cracking for nickel-based superalloy includes voids nucleation, growth and aggregation. Based on the obtained critical parameters, the evolutions of stress, strain, strain rate, temperature and damage were discussed by numerical simulation. By comparing the experiment results and simulation results, the Normalized Cockcroft and Latham (NCL) model was determined as the most suitable model. Considering the influences of temperature and strain rate on the damage threshold, the NCL model of Inconel 718 alloy was established by high-temperature tensile test. Based on the above results, it is found that the maximum shear stress promotes the plastic deformation, which provides necessary conditions for the generation of defects, and the maximum principal stress induces the generation of voids and expansion of micro-cracks, which directly leads to the central cracking. The essence of central cracking is ductile fracture under tensile stress.

Zastosowanie proporcjonalnych modeli uszkodzeń w analizie niezawodności na przykładzie układu antropotechnicznego

Gumiński R., Radkowski S., Sobczykiewicz W.

Problemy Maszyn Roboczych

2004

Z. 23

57--67

W pracy zaprezentowano zastosowanie proporcjonalnych modeli uszkodzeń w analizie niezawodności. We wprowadzeniu omówiono podstawy teoretyczne, a następnie przedstawiono przykład analizy niezawodności układu hydraulicznego z uwzględnieniem wpływu warunków pracy na niezawodność operatora.

In the paper is explained the use of Proportional Hazards models in reliability analysis. At the beginning is presented a theoretical consideration on some application aspects. Next is presented an example of operator failure impact on reliability of hydraulic system.

Error estimation and adaptivity for nonlinear FE analysis

Huerta A., Rodriguez-Ferran A., Diez P.

International Journal of Applied Mathematics and Computer Science

2002

Vol. 12, no 1

59-70

An adaptive strategy for nonlinear finite-element analysis, based on the combination of error estimation and h-remeshing, is presented. Its two main ingredients are a residual-type error estimator and an unstructured quadrilateral mesh generator. The error estimator is based on simple local computations over the elements and the so-called patches. In contrast to other residual estimators, no flux splitting is required. The adaptive strategy is illustrated by means of a complex nonlinear problem: the failure analysis of a single-edge notched beam. The quasi-brittle response of concrete is modelled by means of a nonlocal damage model.