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Fracture analysis for viscoelastic creep using peridynamic formulation

Azizi Muhammad Azim, Mohd Zahari Mohd Zakiyuddin, Abdul Rahim Sharafiz, Azman Muhamad Amin

Journal of Theoretical and Applied Mechanics

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2022

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Vol. 60 nr 4

579--591

EN

The purpose of this paper is to provide a peridynamic (PD) model for the prediction of the viscoelastic creep deformation and failure model. The viscoelastic characteristic consists of several stages, namely primary creep, secondary creep, tertiary creep and fracture. A non- linear viscoelastic creep equation based on the internal state variable (ISV) theory covering four creep stages and PD equations are used. The viscoelastic equation is inserted into the PD equation to derive a PD model with two time parameters, i.e., numerical time and vis- coelastic real time. The parameters of the viscoelastic equation are analyzed and optimized. A comparison between numerical and experimental data is performed to validate this PD model. The new PD model for nonlinear viscoelastic creep behavior is confirmed by an ac- ceptable similarity between the numerical and experimental creep strain curves with an error of 15.85%. The nonlinearity of the experimental and numerical data is sufficiently similar as the error between the experimental and numerical curves of the secondary stage strain rate against the load is 21.83%. The factors for the errors are discussed and the variation of the constants in the nonlinear viscoelastic model is also investigated.

2

Research on high-temperature compression and creep behavior of porous Cu-Ni-Cr alloy for molten carbonate fuel cell anodes

Li W., Chen J., Liang H., Li C.

Materials Science Poland

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2015

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Vol. 33, No. 2

356--362

EN

The effect of porosity on high temperature compression and creep behavior of porous Cu alloy for the new molten carbonate fuel cell anodes was examined. Optical microscopy and scanning electron microscopy were used to investigate and analyze the details of the microstructure and surface deformation. Compression creep tests were utilized to evaluate the mechanical properties of the alloy at 650 degrees C. The compression strength, elastic modulus, and yield stress all increased with the decrease in porosity. Under the same creep stress, the materials with higher porosity exhibited inferior creep resistance and higher steady-state creep rate. The creep behavior has been classified in terms of two stages. The first stage relates to grain rearrangement which results from the destruction of large pores by the applied load. In the second stage, small pores are collapsed by a subsequent sintering process under the load. The main deformation mechanism consists in that several deformation bands generate sequentially under the perpendicular loading, and in these deformation bands the pores are deformed by flattering and collapsing sequentially. On the other hand, the shape of a pore has a severe influence on the creep resistance of the material, i.e. every increase of pore size corresponds to a decrease in creep resistance.

3

Analysis of PA 6 nanocomposites — indentation and creep behavior as a function of temperature and load level using different indentation techniques

Schöne J., Tondl D., Lach R., Rybnicek J., Grellmann W.

Polimery

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2014

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T. 59, nr 10

722--728

EN

The short-term performance (Martens hardness and indentation modulus) and the time-dependent creep behavior of polyamide 6 (PA 6) and two PA 6 nanocomposites containing 3.5 wt % montmorillonite (MMT) or 5 wt % halloysite nanotubes (HNT) were analyzed by different depth-sensing indentation techniques in the nano-, micro- and macro-range of loading as a function of applied load (0.08— 100 N) and temperature (-80—60 °C). Additionally, WAXD and DSC measurements were made to establish the morphology-property relationships of the investigated materials while taking into account the skin-core structure of the injection-moulded samples.

PL

Za pomocą techniki DSI (Depth Sensing Indentation), z zastosowaniem głębokości wciskania z zakresu nano, mikro oraz makro, analizowano zależność twardości indentacyjnej, twardości Martensa, modułu wciskania oraz pełzania pod obciążeniem nanokompozytów poliamidu 6 od temperatury (-80—60 °C) i przyłożonej siły (0,08—100 N). Badano nanokompozyty PA 6 napełnione montmorylonitem (3,5 % mas.) oraz nanorurkami haloizytu (5 % mas.). Dodatkowo przy użyciu technik WAXD oraz DSC oceniano wpływ morfologii badanych materiałów na ich właściwości, z uwzględnieniem efektu skin-core w próbkach otrzymanych metodą wtryskiwania.

4

In-situ testing and heterogeneity of UFG Cu at elevated temperatures

Petrenec M., Král P., Dvořák J., Svoboda M., Sklenička V.

Journal of Achievements in Materials and Manufacturing Engineering

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2014

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Vol. 62, nr 2

69--74

EN

Purpose: The motivation of present investigation is the study of deformation-induced processes during in-situ tensile and compression test at elevated temperature in order to elucidate the role of the microstructure changes during creep testing. Design/methodology/approach: Experiments were conducted to investigate deformation-induced processes during in-situ tensile test at elevated temperature. Findings: It was found that creep resistance of UFG pure Al and Cu is considerably improved after one ECAP pass in comparison with coarse grained material, however, further repetitive pressing leads to a noticeable deterioration in creep properties of ECAP material. Researches limitations/implications: In the present work was found that ultrafine-grained microstructure is instable and significant grain growth has already occurred during heating to the testing temperature. Originality/value: The experiments conducted on pure Al and Cu found that their creep resistance is considerably improved after one ECAP pass in comparison with unpressed material.