Abstract:Traditionally, the material's stress-strain relationship is acquired from uniaxial testing, which is widely used to describe its behavior under plastic deformation. When it comes to traditional hardness tests, such as in the Brinell, Knoop, Rockwell, and Vickers, they have been mostly used as a way to assess the capability a material has to resist plastic deformation. The technique developed and presented here has gone beyond that by determining other material properties in addition to hardness. This is perfor… Show more
“…The finite element method and a gradient-based multivariable search method were used in the identification approach. In this contribution, a parametric identification tool developed by Machado and Malcher (2019), called MCI, was used.…”
Section: Calibration Proceduresmentioning
confidence: 99%
“…The finite element method and a gradient-based multivariable search method were used in the identification approach. In this contribution, a parametric identification tool developed by Machado and Malcher (2019), called MCI, was used. By Figure 13, it is possible to observe the flowchart of the parametric identification scheme.Figure 13.Parametric identification scheme by Machado and Malcher (2019).…”
Section: Calibration Of Materials Parametersmentioning
This contribution proposes a study of the mechanical behavior from damage to fracture of normalized and annealed samples of AISI 4340 steel. Besides, a numerical study in a security device of offshore industry is conducted. Experimental tests were initially performed on smooth and notched cylindrical specimens subjected to monotonic tension as well as on rectangular specimens subjected to pure shear and a combination of shear and tension loads. Such experimental tests were selected to observe different combinations of the stress triaxiality and the normalized third invariant concerning the stress state. The two types of heat treatments were considered to achieve different levels of ductility and verify their influence on the fracture mode of the alloy. The approach based on the second invariant of the deviatoric stress tensor ( J 2), with nonlinear isotropic hardening, is assumed to describe the mechanical behavior of the material in axisymmetric and three-dimensional numerical simulations. Finite elements simulations were carried out to analyze the performance of a simplified version of a mechanism of a blow-out preventer-BOP valve. The experimental and numerical curves of force versus displacement were compared, highlighting the effect of the stress triaxiality, the third invariant and calibration condition on the behavior of the material. The evolution of the equivalent plastic strain was plotted, and the fracture onset compared with its maximum value. The results show that the AISI 4340 alloy is highly dependent on the stress triaxiality and third invariant. Moreover, it can be concluded that different calibration conditions for the isotropic hardening curve can result in different levels of forces for the correct performance of the BOP in a critical situation.
“…The finite element method and a gradient-based multivariable search method were used in the identification approach. In this contribution, a parametric identification tool developed by Machado and Malcher (2019), called MCI, was used.…”
Section: Calibration Proceduresmentioning
confidence: 99%
“…The finite element method and a gradient-based multivariable search method were used in the identification approach. In this contribution, a parametric identification tool developed by Machado and Malcher (2019), called MCI, was used. By Figure 13, it is possible to observe the flowchart of the parametric identification scheme.Figure 13.Parametric identification scheme by Machado and Malcher (2019).…”
Section: Calibration Of Materials Parametersmentioning
This contribution proposes a study of the mechanical behavior from damage to fracture of normalized and annealed samples of AISI 4340 steel. Besides, a numerical study in a security device of offshore industry is conducted. Experimental tests were initially performed on smooth and notched cylindrical specimens subjected to monotonic tension as well as on rectangular specimens subjected to pure shear and a combination of shear and tension loads. Such experimental tests were selected to observe different combinations of the stress triaxiality and the normalized third invariant concerning the stress state. The two types of heat treatments were considered to achieve different levels of ductility and verify their influence on the fracture mode of the alloy. The approach based on the second invariant of the deviatoric stress tensor ( J 2), with nonlinear isotropic hardening, is assumed to describe the mechanical behavior of the material in axisymmetric and three-dimensional numerical simulations. Finite elements simulations were carried out to analyze the performance of a simplified version of a mechanism of a blow-out preventer-BOP valve. The experimental and numerical curves of force versus displacement were compared, highlighting the effect of the stress triaxiality, the third invariant and calibration condition on the behavior of the material. The evolution of the equivalent plastic strain was plotted, and the fracture onset compared with its maximum value. The results show that the AISI 4340 alloy is highly dependent on the stress triaxiality and third invariant. Moreover, it can be concluded that different calibration conditions for the isotropic hardening curve can result in different levels of forces for the correct performance of the BOP in a critical situation.
“…A total of 7 specimens were manufactured: 4 for annealed AISI 4340 alloy and 3 for AA6101-T4 alloy. For the AA6101-T4 alloy, the experimental data were taken from Malcher [46], assuming a smooth cylindrical specimen and two notched cylindrical specimens with a notch radius of 6 and 10 mm. Besides that, for the AISI 4340 alloy, the experimental data were taken from Morales [2], assuming a smooth cylindrical specimen and three cylindrical notched specimens with a notch radii of 4, 6, and 10 mm.…”
Section: Materials Descriptionmentioning
confidence: 99%
“…For both materials, the smooth cylindrical specimens, under tensile load, resulting in the experimental reaction and optimized curve, through the multivariable search method based on the gradient proposed by Machado and Malcher [46] and Machado [47], for calibration of material properties. In this case, the Kleinermann and Ponthot [48] curve parameters were also calibrated, equation ( 20), used to represent the behavior of the isotropic hardening curve of materials through four parameters: σ y0 , σ ∞ , ξ, δ.…”
Section: Discretization and Calibration Of Materials Parametersmentioning
This paper provides a numerical assessment of the ductile fracture of the AA6101 and AISI 4340 alloys using the Lemaitre and Gurson models.The simulations were carried out to verify the evolution of the accumulated plastic strain at fracture, assuming the high range of the triaxiality ratio, applying monotonic tensile loads on smooth and notched cylindrical specimens. The numerical strategy was structured for the Lemaitre and Gurson models, from establishing a non-linear system of equations using an implicit integration algorithm and solving the non-linear equation system using the Newton-Raphson method. When assessing the numerical and experimental results, it was observed that the cumulative plastic strain at the fracture decreases with the increasing levels of the triaxiality ratio for both alloys and models. On the one hand, the Lemaitre model was more optimistic than the experimental results. On the other hand, Gurson's model proved to be more conservative in its prediction of ductile fracture. Regarding determining the fracture onset, in general, both models showed good predictive capacity. However, the numerical results for the aluminum alloy presented more in agreement with experimental data than for the AISI 4340 alloy. In the end, assuming the determination of the level of displacement at fracture, the Gurson's model has the best performance. In this sense, for a high level of triaxiality ratio, the Gurson porous material can be recommended to describe the mechanical behavior of the material at fracture.
“…The main objective of the optimization process used is to find, simultaneously, a set of damage parameters that is capable of minimizing the difference between the estimated and observed lives of the tension-compression and torsional tests for each of the analyzed materials. For this, a method based on the gradient of the objective function was applied to obtain the optimized values of the set of parameter p , see Machado and Malcher (2014). Finally, the Table 6 presents the damage parameters found at the end of the process.…”
Section: Materials Parameters and Loading Pathsmentioning
In this contribution, a modification and application of the Lemaitre damage evolution law is proposed for the problem of fatigue life estimate under low number of cycles. For this, the denominator of damage, considered constant for Lemaitre, was replaced by a function dependent on the stress triaxiality. The new function has a nonlinear and thermodynamically consistent behavior. In addition, the evolution law of the backstress tensor is adopted as proposed by Desmorat, where there is no saturation of the limit value. The formulation is implemented in an academic tool for analysis at one Gauss point, through an implicit integration strategy of the flow equations. The Newton-Raphson method is used to solve a system of nonlinear equations, with two tensor and two scalar equations. Thus, in order to demonstrate the robustness of the model, experimental data from the literature for SAE 1045 and S460N steels are adopted. Proportional and nonproportional axial, torsional and multiaxial loading paths are simulated. Finally, the results have shown that the modification formulation is a good strategy to control the damage evolution in predicting fatigue life. In this sense, the calculated lives by the new proposal are within a scatter band of factor three, both under normal or torsional uniaxial loading conditions, as well as proportional or nonproportional multiaxial conditions.
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