Steel grade 14MoV6 3 is used for manufacturing of boilers and steam pipelines designed for steam temperatures up to 560°C. This paper presents the numerical simulation of a CT-specimen, using the ...finite element method. The analysis was performed using Ansys Workbench R21, and represents the initial stage of extensive research involving the behaviour of 14MoV6 3 steel. The goal was to simulate the real experimental conditions, including boundary conditions and loads, which were defined in accordance with relevant standards, and to obtain representative results. The temperature dependent mechanical properties needed for the simulation of plastic behaviour of such specimens under tensile loads were obtained from the experimental data and the literature.
The phase-field approach to fracture modelling has gained much attention in the field of computational fracture mechanics in the past decade. The phase-field approach eliminates the need for the ...numerical tracking of the sharp crack discontinuities by the smooth transition of a scalar damage field whose value differentiates between the broken and intact material states. Its variational based approach has been proven to be thermodynamically consistent and able to solve complex fracture processes. Consequently, many different phase-field fracture models have emerged. In this contribution, a few well-known phase-field models for brittle fracture modelling have been implemented within the staggered algorithm with stopping criterion based on the control of the residual norm, recently developed by the authors. The implementation has been conducted within the commercial finite element software Abaqus and expanded to the three-dimensional settings. The experimental validation of the numerical models is then conducted on the tensile, compact tension (CT) and single edge notched bend (SENB) specimens made of the thermoplastic polymer, polymethylmethacrylate (PMMA). It has been demonstrated that with a suitable choice of the length scale parameter, the developed staggered phase-field fracture models can provide valid prediction of the brittle crack initiation and propagation under quasi-static loading conditions.
•Effect of holes along the crack flanks on the fatigue crack growth rate.•Numerical study using the cumulative plastic deformation at the crack tip.•Parametric study on the diameter of holes and the ...distance between them.•Experimental results on a CT specimen to validate the numerical model.
The effect of drilling two symmetric holes along the crack flanks on the fatigue crack growth (FCG) rate was evaluated numerically. The FCG increases (decreases) when the crack tip is behind (ahead) the holes. This behaviour is enlarged both by increasing the diameter of the holes and by reducing the distance between them. This is consequence of the geometrical effect, which modifies the plastic zone size. Experimental work validated the numerical model, indicating that that cumulative plastic strain at the crack tip is an adequate crack driving force and that cyclic plastic deformation is the main damage mechanism of FCG.
The next generation Concentrated Solar Power (CSP) plants integrated with Thermal Energy Storage (TES) offer a promising solution for dispatchability, reliability, and economic concerns associated ...with renewable energy technologies. However, the expected operational life of up to 30 years proves to be a major challenge due to the impact of high temperatures and corrosive eutectic salts utilised in the latent heat TES systems. Additionally, the system is under varying degrees of stress that can accelerate corrosion mechanisms. Unfortunately, this stress corrosion relationship is often neglected during the material compatibility assessment. This study utilises a novel static immersion testing approach with three designs of modified Compact Tension (CT) specimens manufactured from AISI 316L to investigate the interaction of alloys under stress with various eutectic salts at up to 750 °C for up to 1000 Hours. The results indicate that oxidation is accelerated up to four times and Intergranular Corrosion (IGC) up to two times in the high-stress region of the test samples. Furthermore, the findings suggest that static immersion testing using CT specimens can be regarded as an effective approach to assess the influence of stress on corrosion and conduct a reliable material assessment for latent heat TES systems and CSP plants.
•Stress severely affects corrosion rate/propagation within alloys in molten salt/air•Prestressed 316L compact tension specimen used to examine stress assisted corrosion•Oxidation accelerated up to four times due to stress at 650 °C in air•Stress accelerated IGC up to two times at 650 °C in NaCl/Na2CO3 salt•Stress induced breakdown of oxide layer in solar salt leads to localised corrosion
•The relation between Q-term and A2(t)-term is compared and discussed.•A creep toughness modification method is presented based on NSW model.•A modified TDFAD method is presented based on C(t)-A2(t) ...theory.•The modified TDFAD curves for various CT specimens under various creep conditions are given.
Due to the potential influence of constraint effect on failure assessment, a link is needed to bridge the constraint effect characterized by higher order term asymptotic solution and time dependent failure assessment diagram (TDFAD). In this paper, a modification method for creep toughness incorporating C(t)-A2(t) theory is proposed based on Nikbin-Smith-Webster model. The relation between Q-term and A2(t)-term is also presented for creep crack. Results show that the creep toughness can be influenced by constraint parameter remarkably. A modified TDFAD is proposed based on C(t)-A2(t) solution. Based on the creep data of 316H stainless steel and various compact tension specimens, the modified TDFAD curves considering constraint effect characterized with A2(t)-term is presented and discussed, which indicates the important role of constraint effect on the assessment boundary of TDFAD. The research given in this paper can provide an alternative method in which the constraint effect can be included in TDFAD under high temperature.
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To ensure the safe operation of nuclear power plants, the status of the reaction pressure vessel needs to be monitored in real time. The fracture toughness of the domestic A508-Ⅲ steel, which is the ...main material, can be used as the primary indicator to reflect its condition. Recently, the size of specimens used for nuclear material testing and analysis is gradually decreasing, and this trend helps to improve the accuracy and efficiency of testing. The fracture behavior of mini-CT (1/6CT) specimens from a meso-scale perspective was studied in this paper, to reveal the fracture mechanism for a better understanding of the material properties. The uniaxial tensile testing of domestic A508-Ⅲ steel was carried out with the aim of gaining insight into this fracture behavior. Based on the testing results, the Ramberg-Osgood mechanical intrinsic model and the GTN (Gurson-Tvergaard-Needleman) meso-damage model, those can accurately describe the mechanical behavior of the material, were constructed. The model parameters were also calculated and determined based on the testing data, and the reliability of the models was verified by comparing the testing data with the simulation results. Subsequently, fracture toughness tests of 1/6CT specimens at different temperatures were also conducted to understand the effect of temperature on the fracture properties of the material by analyzing the morphological characteristics of the fracture. The results show that the width of the fracture toughness zone shrinks from 43 μm to 10 μm, and the average toughness size shrinks from 0.3 μm to 0.05 μm as the temperature decreases from -100 ℃ to -130 ℃. The plastic deformability of the material becomes more brittle as the temperature decreases. Based on the constructed mechanical intrinsic model and the GTN meso-damage model, the 1/6CT specimen was analyzed from crack sprouting and expansion to failure fracture using finite elements, and the results show that the J-R curve decreases with the decrease of temperature, and fracture toughness value (JIC) and crack extension length (Δa) decrease by 43% and 3% respectively, with an error of no more than 5%. This indicates that the numerical method based on the GTN meso-damage model is a simple and effective way to study the fracture behavior of mini-CT specimens.
The FDM (Fused Deposition Modelling) additive manufacturing process is characterised by a large number of process variables that determine the mechanical properties and quality of the manufactured ...parts. When printing layer by layer, the filaments constituting the layer are welded on the one hand between them in the same layer and on the other hand between the superimposed layers, this welding develops on the contact surfaces (raster width) along the deposited filaments. The quality of this welding determines the resistance to crack propagation between filaments and between layers. This article aims to study the effect of the width of the raster on the resistance to crack propagation in a structure obtained by FDM.We have developed an experimental approach from CT specimens to determine the tensile strength of polylactic acid (PLA) polymers, considering the J-Integral method. And given the complexity of the problem, three cases of raster width (l=0.42 mm, l=0.56 mm and l=0.68 mm) have been treated.According to the results obtained (J, ∆a), the resistance to crack propagation in the parts printed by FDM seems to be better when the width of the filament is small. Indeed, the energy necessary to break the specimen is relatively greater than in the case of a larger width. This finding was confirmed by comparing the values of J for a given advancement of the crack for the three cases studied.In order to present an exhaustive study, we focused on the effect of raster widths (including 0.42 mm, 0.56 mm to 0.68 mm) on the crack propagation of printed PLA. This study is in progress for other printing parameters. To highlight the cracking mechanisms, microscopic observations will be developed in greater depth at the SEM.Our analysis can be used as decision support in the design of FDM parts. In effect, we can choose the raster width that would provide the resistance to crack propagation desired for a functional part.In this article, we analysed the damage mechanism of CT specimens printed by FDM. This subject represents a new direction for many lines of research. For our study, we used the J-Integral theoretical approach to study the fracture behaviour of these parts by determining the resistance curves (J-∆a).
This paper investigates the fracture response and crack-tip constraint of two typical compact tension specimens. They are pre-cracked plain-sided and side-grooved specimens. In order to clarify the ...significant effects of geometric parameters on the crack-tip stress fields, an extensive series of detailed 3D elastic–plastic finite element analyses have been carried out. Taking the standard ratio of geometric parameters as a basis, several non-standard geometric parameters are adopted in the calculation for comparison, including specimen thickness, width, crack length. Accordingly, the variation of local
J
-integral and crack-tip opening displacement have been vigorously investigated over the crack front. Most importantly, the crack-tip stress fields are analyzed in detail with the emphasis on the stress triaxiality and opening mode stress. Furthermore, the crack-tip plastic strain and deformation are compared under small-scale yielding and large-scale yielding between plain-sided and side-grooved specimens, and the constraint parameter
Q
is employed to explain the distribution of the near-tip plastic strain. Through the vigorous research work, the variation of fracture behavior caused by geometric parameters is reasonably explained and understood.
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