International Journal of Material Forming最新文献

Abstract

Induction hardening is a heat surface treatment technique widely employed for steel components in order to improve their fatigue life without affecting the metallurgy of the bulk material. The control of the treated components goes through the prediction and the optimization of the induction hardening process parameters. The aim of this work is to propose an approach based on artificial intelligence technique to predict the in-depth hardness profile. For this purpose, experimental tests were first carried out on 300M steel bar and C45 steel spur-gear under single and double frequencies, respectively. Intermediate variables were then generated to be used as input data. Data-driven model based on XGBoost library was finally developed. It was found that the proposed approach predicts with good agreement the hardness profiles and can be used in induction treatment process optimization.

Abstract

Zirconium alloys are widely used as structure materials in nuclear fuel assembly. However, the poor forming performance of zirconium alloy restricts its application and consequently hinders the development of nuclear industry. In this study, the concept of strain limit is defined, and the influencing mechanisms of different mechanical properties of zirconium alloys on the strain limit of tension-compression area and equi-biaxial area are revealed. The research shows that the variation of sheet thickness t and strength coefficient K has little impact on the strain limit of zirconium alloy. The increase of strain hardening exponent n will significantly raise the strain limit of zirconium alloys in both the tension-compression area and equi-biaxial area. the Lankford coefficient R can improve the strain limit of tension-compression area, but not the equi-biaxial area. Besides, the influencing mechanisms of R and n on the strain limit of zirconium alloy are different. The value of n mainly improves the strain limit by increasing the base point of forming limit curve while the value of R primarily increases the strain limit by changing the slopes of the strain paths in the tension-compression area. Therefore, the value increase of R and n can be considered as an effective way to improve the forming performance of zirconium alloys.

Surrogate models, both polynomial and ANN-based (artificial neural networks), are developed to predict the rolling load in cold rolling of flat metals. An accurate but fast model was developed to serve as high-fidelity model for the training of the machine learning algorithms, allowing for large sampling sizes (up to 1000 samples) with different sampling methods, a number of eight input parameters, and various configurations of surrogate models. The ANN-based models have shown excellent predictive abilities provided that the training sampling is sufficiently large (more than 500 elements). In contrast, polynomial models converge much rapidly to their optimal accuracy (samplings of tens of elements) but their predictive ability is more limited, unless the order of the polynomials is increased. The latin hypercube sampling was more efficient than the random sampling in all cases.

The use of carbon fiber reinforced polymer composites has increased with the increased need for high-strength, low-density materials, particularly in the aerospace industry. Stretch broken carbon fiber (SBCF) is a form of carbon fiber created by statistically distributed breakage of aligned fibers in a tow at inherent flaw points, resulting in a material constituted of collimated short fibers with an average length larger than chopped fibers. While continuous carbon fiber composites have desirable material properties, the limited ability to form in complex geometries prevents their wide adoption. SBCF composites exhibit pseudo-plastic deformation that can potentially enable the use of traditional metal forming techniques like stamping and press forming, widely used for mass production applications. To investigate the formability of carbon fiber reinforced polymer composites prepared with either continuous or stretch broken Hexcel IM-7 12 K fibers and impregnated with Huntsman RDM 2019–053 resin, hydraulic bulge testing was performed at atmospheric pressure and elevated temperature to explore the strain behavior under biaxial stress conditions for the material system. Results based on deformation of surface patterning, bulge apex displacement and measurement of the bulge internal surface and volume, support the enhanced formability of the SBCF material when compared to its continuous counterpart. The SBCF enhanced formability is characterized by an axisymmetric stress response and a failure mechanism similar to the one observed for sheet metal.

The deep drawability of additively manufactured stainless steel sheets with a core structure is investigated. By fracture forming limit diagrams it is shown that the additively manufactured sheets reveal good formability. The deep drawing process is analyzed numerically and the numerical models are validated experimentally. The main failure mode is a fracture of the face sheets. No severe deformation of the core structure was encountered, leading to the fact that the parts keep their structural integrity after the deep drawing process. It is shown that the process forces can reasonably be predicted by a modified Siebel’s method. A process window diagram is derived, e.g. showing a maximum deep drawing ratio β_max = 1.4 for honeycomb structures with a relative core density of ρ_core = 0.22.

In this paper, hot gas pressure forming (HGPF) of titanium alloy irregularly profiled tubular component using laser-welded tube was studied by both simulation and experiment. Uniaxial tensile tests of base metal (BM) under different conditions were performed to determine the true stress–strain curves. The forming process was optimized by finite element simulation and response surface method (RSM). Results show that the forming pressure increases with the decreasing temperature and increasing strain rate. Microstructures of BM are sensitive of forming temperature, strain and strain rate. Wrinkling and local thinning of the component can be avoided by a reasonable initial tube diameter during the forming. Ideal weld position should be determined to avoid the failure of the weld seam (WS). A qualified TC2 titanium alloy component with both high dimensional accuracy and good post-form properties was successfully formed by HGPF using the optimized forming parameters. The total heating and forming time of the tube was less than 30 min. Both of the post-form properties and microstructures of the component were almost the same with the initial material.

It is almost commonplace to say that physics-based constitutive models developed to characterize the mechanical behavior of materials are to be preferred over phenomenological models. However, the constitutive relations offered by physics-based approaches are oftentimes too involved to be handled in finite element (FE) simulations for practical applications. There is a demand for physics-based, yet robust and user-friendly models, and one such model will be highlighted in this article. A simple constitutive model developed recently by Bouaziz to extend the classical physics-based Kocks-Mecking model provides a viable tool for modelling a broad range of materials – beyond the single-phase coarse-grained materials it was initially devised for. The efficacy of the model was put to the test by investigating its applicability for different materials. A broad interval of the true stress vs. true strain curve was studied by the measurement-in-neck-section method in the uniaxial tensile mode for six types of metallic materials, and simulations using the finite element method emulating the experimental conditions were developed. In this way, the engineering stress-strain curves were obtained corresponding to the true stress-strain curves for these materials. A comparison of the numerical simulations of the tensile behaviour of all six materials with the experimental results for a broad range of strains showed that among the models trialled, the Bouaziz model was the best-performing one. The proposed model can be recommended for use in FE simulations of the mechanical behaviour of engineering structures as a viable alternative to complex physics-based or simplistic phenomenological constitutive models.