Environment-assisted crack nucleation in La(Fe,Mn,Si)13-based magnetocaloric materials

A method for separating the work of impact into two parts - the work of the crack nucleation and that of crack growth - which consists in testing two samples with the same stress concentrators and different cross-sectional dimensions at the notch site is developed. It is assumed that the work of crack nucleation is proportional to the width of the sample face on which the crack originates and the specific energy of crack formation, whereas the work of the crack growth is proportional to the length of crack development and the specific crack growth energy. In case of the sample fracture upon testing, the crack growth length is assumed equal to the sample width. Data on the work of fracture of two samples and their geometrical dimensions at the site of the notch are used to form a system of two linear equations in two unknowns, i.e., the specific energy of crack formation and specific energy of crack growth. The determined specific energy values are then used to calculate the work of crack nucleation and work of crack growth. The use of the analytical method improves the accuracy compared to graphical - extrapolative procedures. The novelty of the method consists in using one and the same form of the notch in test samples, thus providing the same conditions of the stress-strain state for crack nucleation and growth. Moreover, specimens with different cross-section dimensions are used to eliminate the scale effects. Since the specific energy of the crack nu-cleation and specific energy of the crack growth are independent of the scale factor, they are determined only by the properties of the metal. Introduction the specific energy of crack formation and growth makes possible to assign a specific physical meaning to the fracture energy.

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Nonlinear Fracture Mechanics Analysis Considering Material Inhomogeneity of Welded Joints

Impact ◽

10.21820/23987073.2019.10.105 ◽

2019 ◽

Vol 2019 (10) ◽

pp. 105-107

Author(s):

Hiroshi Okada

Keyword(s):

Fracture Mechanics ◽

Solid Mechanics ◽

Crack Nucleation ◽

Intensity Factors ◽

Nonlinear Fracture Mechanics ◽

Material Inhomogeneity ◽

Computational Fracture Mechanics ◽

New Methods ◽

Nonlinear Fracture ◽

Mechanics Analysis

Professor Hiroshi Okada and his team from the Department of Mechanical Engineering, Faculty of Science and Technology, Tokyo University of Science, Japan, are engaged in the field of computational fracture mechanics. This is an area of computational engineering that refers to the creation of numerical methods to approximate the crack evolutions predicted by new classes of fracture mechanics models. For many years, it has been used to determine stress intensity factors and, more recently, has expanded into the simulation of crack nucleation and propagation. In their work, the researchers are proposing new methods for fracture mechanics analysis and solid mechanics analysis.

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Influence of post-welding tempering on mechanical behavior of friction welded joints from medium-carbon steels during tensile test

Voprosy Materialovedeniya ◽

10.22349/1994-6716-2020-102-2-40-49 ◽

2020 ◽

pp. 40-49

Author(s):

A. S. Atamashkin ◽

E. Yu. Priymak ◽

N. V. Firsova

Keyword(s):

Mechanical Behavior ◽

Welded Joints ◽

Welded Joint ◽

Crack Nucleation ◽

Carbon Steels ◽

Uniaxial Tensile ◽

Medium Carbon ◽

Uniaxial Tensile Testing ◽

Rotary Friction Welding ◽

Medium Carbon Steels

The paper presents an analysis of the mechanical behavior of friction samples of welded joints from steels 30G2 (36 Mn 5) and 40 KhN (40Ni Cr 6), made by rotary friction welding (RFW). The influence of various temperature conditions of postweld tempering on the mechanical properties and deformation behavior during uniaxial tensile testing is analyzed. Vulnerabilities where crack nucleation and propagation occurred in specimens with a welded joint were identified. It was found that with this combination of steels, postweld tempering of the welded joint contributes to a decrease in the integral strength characteristics under conditions of static tension along with a significant decrease in the relative longitudinal deformation of the tested samples.

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Crack Nucleation Mechanism of Austempered Ductile Iron during Tensile Deformation

MATERIALS TRANSACTIONS ◽

10.2320/matertrans.47.82 ◽

2006 ◽

Vol 47 (1) ◽

pp. 82-89 ◽

Cited By ~ 4

Author(s):

Zenjiro Yajima ◽

Yoichi Kishi ◽

Ken’ichi Shimizu ◽

Hideharu Mochizuki ◽

Toshiki Yoshida

Keyword(s):

Ductile Iron ◽

Tensile Deformation ◽

Crack Nucleation ◽

Nucleation Mechanism ◽

Austempered Ductile Iron

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Selective Anisotropy of Mechanical Properties in Inconel718 Alloy

Materials ◽

10.3390/ma14143869 ◽

2021 ◽

Vol 14 (14) ◽

pp. 3869

Author(s):

Yu Liang ◽

Jun Ma ◽

Baogang Zhou ◽

Wei Li

Keyword(s):

Solid Solution ◽

Crack Nucleation ◽

Rolling Direction ◽

Mechanical Anisotropy ◽

Solution Temperature ◽

Weak Anisotropy ◽

Nucleation Sites ◽

Micro Cracks ◽

Δ Phase ◽

Rupture Properties

Mechanical anisotropy behaviors are investigated in slightly rolled Inconel718 alloy with string-like δ phase and carbides produced during various solid-solution and aging treatments. A weak anisotropy in the strengths and rupture properties at 650 °C is visible, whereas ductility, i.e., reduction in area (RA) and impact toughness (CVN), presents a sound anisotropy behavior. MC carbides promote the operation of slip systems and thus are conducive to weakening the strength anisotropy. The RA anisotropy mainly stems from high-density δ phase particles that provide more crack nucleation sites and stimulate rapid propagation because of the shorter bridge distance between micro-cracks at the rolling direction. In contrast, CVN anisotropy arises from both δ phase and carbides at a lower solid-solution temperature of 940 °C but only depends on carbides at 980 °C where the δ phase fully dissolves. Apart from dislocation motions operated at room temperature, the activated grain boundary processes are responsible for the weak anisotropy of rupture properties at the elevated temperature. This work provides a guideline for technological applications in the hot working processes for Inconel718 alloys.

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A Unified Abaqus Implementation of the Phase Field Fracture Method Using Only a User Material Subroutine

Materials ◽

10.3390/ma14081913 ◽

2021 ◽

Vol 14 (8) ◽

pp. 1913

Author(s):

Yousef Navidtehrani ◽

Covadonga Betegón ◽

Emilio Martínez-Pañeda

Keyword(s):

Phase Field ◽

Crack Nucleation ◽

Crack Density ◽

Contact Problems ◽

Element Mesh ◽

Robust Implementation ◽

Current Implementation ◽

User Material Subroutine ◽

Complex Crack ◽

Monolithic Solution

We present a simple and robust implementation of the phase field fracture method in Abaqus. Unlike previous works, only a user material (UMAT) subroutine is used. This is achieved by exploiting the analogy between the phase field balance equation and heat transfer, which avoids the need for a user element mesh and enables taking advantage of Abaqus’ in-built features. A unified theoretical framework and its implementation are presented, suitable for any arbitrary choice of crack density function and fracture driving force. Specifically, the framework is exemplified with the so-called AT1, AT2 and phase field-cohesive zone models (PF-CZM). Both staggered and monolithic solution schemes are handled. We demonstrate the potential and robustness of this new implementation by addressing several paradigmatic 2D and 3D boundary value problems. The numerical examples show how the current implementation can be used to reproduce numerical and experimental results from the literature, and efficiently capture advanced features such as complex crack trajectories, crack nucleation from arbitrary sites and contact problems. The code developed is made freely available.

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Finite Element Analysis of Magnetic Field Exciter for Direct Testing of Magnetocaloric Materials’ Properties

Energies ◽

10.3390/en14102792 ◽

2021 ◽

Vol 14 (10) ◽

pp. 2792

Author(s):

Wieslaw Lyskawinski ◽

Wojciech Szelag ◽

Cezary Jedryczka ◽

Tomasz Tolinski

Keyword(s):

Magnetic Field ◽

Finite Element ◽

Magnetic Circuit ◽

Homogeneous Magnetic Field ◽

Element Analysis ◽

Mcm Testing ◽

Testing Region ◽

Magnetocaloric Materials ◽

Field Excitation ◽

The Magnetic Field

The paper presents research on magnetic field exciters dedicated to testing magnetocaloric materials (MCMs) as well as used in the design process of magnetic refrigeration systems. An important element of the proposed test stand is the system of magnetic field excitation. It should provide a homogeneous magnetic field with a controllable value of its intensity in the MCM testing region. Several concepts of a magnetic circuit when designing the field exciters have been proposed and evaluated. In the MCM testing region of the proposed exciters, the magnetic field is controlled by changing the structure of the magnetic circuit. A precise 3D field model of electromagnetic phenomena has been developed in the professional finite element method (FEM) package and used to design and analyze the exciters. The obtained results of the calculations of the magnetic field distribution in the working area were compared with the results of the measurements carried out on the exciter prototype. The conclusions resulting from the conducted research are presented and discussed.

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