Experimental investigation of macroscopic material nonlinear behavior and microscopic void volume fraction change for porous materials under uniaxial compression

2019 ◽  
Vol 163 ◽  
pp. 130-138 ◽  
Author(s):  
Eun Sun Lee ◽  
Tae Sik Goh ◽  
Jung Sub Lee ◽  
Jin-Young Heo ◽  
Gi-Baek Kim ◽  
...  
Keyword(s):  
Experimental Investigation ◽  
Porous Materials ◽  
Uniaxial Compression ◽  
Volume Fraction ◽  
Nonlinear Behavior ◽  
Void Volume Fraction ◽  
Void Volume ◽  
Material Nonlinear

scholarly journals Forming Limit Stress Diagram Prediction of Pure Titanium Sheet Based on GTN Model

Materials ◽  
2019 ◽  
Vol 12 (11) ◽  
pp. 1783 ◽  
Author(s):  
Tao Huang ◽  
Mei Zhan ◽  
Kun Wang ◽  
Fuxiao Chen ◽  
Junqing Guo ◽  
...  
Keyword(s):  
Volume Fraction ◽  
Pure Titanium ◽  
Void Volume Fraction ◽  
Void Volume ◽  
Forming Limit ◽  
Stress And Strain ◽  
Gtn Model ◽  
Stress Diagram ◽  
Limit Stress ◽  
Hemispherical Punch

In this paper, the initial values of damage parameters in the Gurson–Tvergaard–Needleman (GTN) model are determined by a microscopic test combined with empirical formulas, and the final accurate values are determined by finite element reverse calibration. The original void volume fraction (f0), the volume fraction of potential nucleated voids (fN), the critical void volume fraction (fc), the void volume fraction at the final failure (fF) of material are assigned as 0.006, 0.001, 0.03, 0.06 according to the simulation results, respectively. The hemispherical punch stretching test of commercially pure titanium (TA1) sheet is simulated by a plastic constitutive formula derived from the GTN model. The stress and strain are obtained at the last loading step before crack. The forming limit diagram (FLD) and the forming limit stress diagram (FLSD) of the TA1 sheet under plastic forming conditions are plotted, which are in good agreement with the FLD obtained by the hemispherical punch stretching test and the FLSD obtained by the conversion between stress and strain during the sheet forming process. The results show that the GTN model determined by the finite element reverse calibration method can be used to predict the forming limit of the TA1 sheet metal.

Determination of mechanical properties of FFF 3D printed material by assessing void volume fraction, cooling rate and residual thermal stresses

2019 ◽  
Vol 25 (10) ◽  
pp. 1661-1683 ◽  
Author(s):  
Rafael Quelho de Macedo ◽  
Rafael Thiago Luiz Ferreira ◽  
Kuzhichalil Jayachandran
Keyword(s):  
Mechanical Properties ◽  
Cooling Rate ◽  
Young’S Modulus ◽  
Thermal Stresses ◽  
Volume Fraction ◽  
Young's Modulus ◽  
Void Volume Fraction ◽  
Void Volume ◽  
Temperature Fields ◽  
Content Type

Purpose This paper aims to present experimental and numerical analyses of fused filament fabrication (FFF) printed parts and show how mechanical characteristics of printed ABS-MG94 (acrylonitrile butadiene styrene) are influenced by the void volume fraction, cooling rate and residual thermal stresses. Design/methodology/approach Printed specimens were experimentally tested to evaluate the mechanical properties for different printing speeds, and micrographs were taken. A thermo-mechanical finite element model, able to simulate the FFF process, was developed to calculate the temperature fields in time, cooling rate and residual thermal stresses. Finally, the experimental mechanical properties and the microstructure distribution could be explained by the temperature fields in time, cooling rate and residual thermal stresses. Findings Micrographs revealed the increase of void volume fraction with the printing speed. The variations on voids were associated to the temperature fields in time: when the temperatures remained high for longer periods, less voids were generated. The Young's Modulus of the deposited filament varied according to the cooling rate: it decreased when the cooling rate increased. The influence of the residual thermal stresses and void volume fraction on the printed parts failure was also investigated: in the worst scenarios evaluated, the void volume fraction reduced the strength in 9 per cent, while the residual thermal stresses reduced it in 3.8 per cent. Originality/value This work explains how the temperature fields can affect the void volume fraction, Young's Modulus and failure of printed parts. Experimental and numerical results are shown. The presented research can be used to choose printing parameters to achieve desired mechanical properties of FFF printed parts.

scholarly journals Experimental determination of the void volume fraction for S235JR steel at failure in the range of high stress triaxialities

2017 ◽  
Vol 62 (1) ◽  
pp. 167-172 ◽  
Author(s):  
P. G. Kossakowski
Keyword(s):  
Volume Fraction ◽  
High Stress ◽  
Material Model ◽  
Tensile Tests ◽  
Void Volume Fraction ◽  
Void Volume ◽  
Advanced Technique ◽  
Quantitative Image ◽  
Critical Void

Abstract This paper is concerned with the critical void volume fraction fF representing the size of microdefects in a material at the time of failure. The parameter is one of the constants of the Gurson-Tvergaard-Needleman (GTN) material model that need to be determined while modelling material failure processes. In this paper, an original experimental method is proposed to determine the values of fF. The material studied was S235JR steel. After tensile tests, the void volume fraction was measured at the fracture surface using an advanced technique of quantitative image analysis The material was subjected to high initial stress triaxialities T0 ranging from 0.556 to 1.345. The failure processes in S235JR steel were analysed taking into account the influence of the state of stress.

scholarly journals Influence of Initial Porosity on Strength Properties of S235JR Steel at Low Stress Triaxiality

2012 ◽  
Vol 58 (3) ◽  
pp. 293-308 ◽  
Author(s):  
P.G. Kossakowski
Keyword(s):  
Volume Fraction ◽  
Stress Triaxiality ◽  
Material Model ◽  
Strength Properties ◽  
Void Volume Fraction ◽  
Void Volume ◽  
Strength Analysis ◽  
Material Structure ◽  
Porosity Effect ◽  
Material Porosity

Abstract The paper discusses the influence of the initial parameters on the strength parameters of S235JR steel at low stress triaxiality. The analysis was performed using the Gurson-Tvergaard-Needleman (GTN) material model, which takes into consideration the material structure. The initial material porosity was defined as the void volume fraction f0. The fully dense material without pores was assumed and the typical and maximum values of porosity were considered for S235JR steel in order to analyse the porosity effect. The strength analysis of S235JR steel was performed basing on the force-elongation curves obtained experimentally and during numerical simulations. Taking into consideration the results obtained, the average values of the initial void volume fraction f0 = 0.001 for S235JR steel is recommended to use in a common engineering calculations for elements operating at low stress triaxiality. In order to obtain more conservative results, the maximum values of f0 = 0.0024 may be used.

The Effects of Material Properties on Crack Tip Constraint and CTOD Fracture Toughness for Commonly Used Pipelines Steels

2020 ◽  
Author(s):  
Yinhui Zhang ◽  
Jian Shuai
Keyword(s):  
Fracture Toughness ◽  
Yield Strength ◽  
Strain Hardening ◽  
Oil And Gas ◽  
Volume Fraction ◽  
Petroleum Industry ◽  
Void Volume Fraction ◽  
Void Volume ◽  
Strain Hardening Exponent ◽  
Material Parameters

Abstract As the main transportation carrier of oil and gas, pipelines play a very important role in the petroleum industry. When the crack-containing pipelines subjected to external loads, the cracks may propagate gradually, and result in serious failure eventually. Therefore, accurately obtaining the fracture toughness is very essential for the safety assessment of the crack-containing pipelines. However, the fracture toughness is not a material intrinsic parameter, but heavily depends on the constraint. To obtain the accurate relationship between the constraint and the fracture toughness for different materials, it is necessary to determine the effects of different material parameters on the change characteristics of the constraint and the fracture toughness. In this work, the commonly used pipelines steels are selected as the research materials. The SENB specimens and the complete Gurson model are used to conduct the simulation with ABAQUS. The material parameters analyzed include strain hardening exponent, yield strength and initial void volume fraction. The results show that for the thinner specimen, the higher strain hardening capacity will result in lower constraint. The higher strain hardening capacity will result in higher constraint for the thicker specimen. For the thinner specimen, the constraint is approximately the same for the materials with different yield strength. The constraint will decrease with the increase of yield strength for the thicker specimen. In the middle range of the thickness of specimen, higher initial void volume fraction will result in higher constraint. For the thicker and thinner specimen, the effect of initial void volume is very weak. As the increase of strain hardening capacity and yield strength, the decreasing degree of the fracture toughness becomes higher in the increasing process of the constraint. A higher initial void volume will result in a lower decreasing degree of the fracture toughness. All of the results indicate that the strain hardening capacity is the main factor affecting the constraint and the fracture toughness. The initial void volume also has a significant effect on the fracture toughness. For the relationship between the constraint and the fracture toughness, the main affecting factor is the strain hardening capacity.

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