A new micro scale FE model of crystalline materials in micro forming process

Micro forming of metals has drawn global attention due to the increasing requirement of micro metal products. However, the size effects become significant in micro forming processes and affect the application of finite element (FE) simulation of micro forming processes. Dividing samples into small areas according to their microstructures and assigning individual properties to each small area are a possible access to micro forming simulation considering material size effects. In this study, a new model that includes both grains and their boundaries was developed based on the observed microstructures of samples. The divided subareas in the model have exact shapes and sizes with real crystals on the sample, and each grain and grain boundaries have their own properties. Moreover, two modelling methods using different information from the microstructural images were introduced in detail. The two modelling methods largely increase the availability of various microstructural images. The new model provides accurate results which present the size effects well

Comparative study of two rolling bond process for super-thick Q235B

In paper, two rolling bond processes for heavy-gauge steel plate Q235B were studied and the processes were simulated by MARC software. The mechanical properties and microstructure at the interface were comparative analyzed for the two bonded plates using different rolling process. Using MARC software analysis for two rolling process, the ratio of equivalent stress in rolling process /yield stress in current temperature from surface to center portion was relatively uniform for rolling bonded

Ex situ analysis of high-strength quenched and micro-alloyed steel during austenitising bending process: numerical simulation and experimental investigation

This paper compares the microstructure and mechanical evolution in a high-strength quenched and micro-alloyed steel during the austenitising bending process. Simulation results indicated a new finding that the stress neutral layer (SNL) tends to move to the tension zone during straining. The hardness gradient detected from the centre to compression/tension zones was resulted from comprehensive factors: First of all, the location of SNL revealed a prominent impact on strength. Second, the dislocation accumulation would be responsible for the hardness gradient on the surfaces. In addition, the overall strength decrease during straining was mainly ascribed to integrated effects of dynamic recovery (DRV) and dynamic recrystallisation (DRX). Apart from that, overall smaller martensite packet size and coarser prior austenite grains resulted in the increased hardness value at a lower bending degree. Also, the high consistency between experimental and simulation results is instructive for the practical forming process of railway spring fasteners

Exact Solutions of Damped Improved Boussinesq Equations by Extended (G′/G)-Expansion Method

With the help of the auxiliary function method, we solved the improved Boussinesq (IBq) equation with fluid dynamic damping and the modified IBq (IMBq) equation with Stokes damping, and we obtained their three types of travelling wave exact solutions, which is an extension service of the numerical simulation and the existence of a solution. From the waveform diagram of IBq equation with hydrodynamic damping, it can be seen that when the propagation velocity of kink wave changes, the amplitude also changes significantly, and it is also found that the kink isolated waveform is significantly asymmetric due to the increase of damping coefficient v, which may be of some value in explaining some physical phenomena. In addition, the symbolic computing software maple makes our computing work easier

Analysis of Springback Behaviour in Micro Flexible Rolling of Crystalline Materials

,is paper presents a constitutive modelling of the polycrystalline thin metal strip under a state of combined loading in microflexible rolling. ,e concept of grained inhomogeneity is incorporated into the classic Chaboche hardening model that accounts for the Bauschinger effect, in order to provide more precise description and analysis of the springback mechanism in the particular forming operation. ,e model is first implemented in the finite element program ABAQUS to numerically predict the stress-strain relationship of 304 stainless steel specimens over a range of average grain sizes. After validation of the developed model by comparison of predicted curves and actual stress-strain data points, it is further applied to predict the thickness directional springback in microflexible rolling of 304 stainless steel strips with initial thickness of 250 μm and reduction changing from 5 to 10%. ,e model predictions show a reasonable agreement with the experimental measurements and have proven to be more accurate than those obtained from the conventional multilinear isotropic hardening model in combination with the Voronoi tessellation technique. In addition, the variation of thickness directional springback along with the scatter effect is compared and analysed in regard to the average grain size utilising both qualitative and quantitative approaches in respect of distinct types of data at different reductions

Micro forming of metallic composites

As the popularisation of electronical devices, the development of micro systems has attracted the attention of the researchers. Therefore, it is crucial to identify the effects of relevant parameters in micro forming process. This study mainly focuses on the impact of holding time in heat treatment process on the properties of Cu-Al-Cu laminate composite materials during micro deep drawing process. The results demonstrate that the Cu-Al-Cu laminate composite material that experiences 10-minute holding time can obtain better properties. Furthermore, a simulation model of the micro forming process is developed and the simulation results are compared with the experimental ones

Local strain analysis of the tertiary oxide scale formed on a hot-rolled steel strip via EBSD

This work presents a fine microstructure and local misorientation study of various oxide phases in the tertiary oxide scale formed on a hot-rolled steel strip via electron back-scattering diffraction (EBSD). Local strain in individual grains of four phases, ferrite (α-Fe), wustite (FeO), magnetite (Fe3O4) and hematite (α-Fe2O3), has been systematically analysed. The results reveal that Fe3O4 has a lower local strain than α-Fe2O3, in particular, on the surface and inner layers of the oxide scale. The multiphase oxides along the cracking or α-Fe2O3 penetration generally develop a high local misorientation. Localised stain along the cracks demonstrates that the misorientation tends to be strong near grain boundaries. The high fraction of small Fe3O4 grains accumulate at the oxide-substrate interface, which leads to a dramatic increase in the intensity of local stain. This variation is due mainly to the phase transformation among the oxide phases, i.e., the Fe3O4 particles during their nucleation and growth. The combined action of stress relief and re-oxidisation is proposed to explain the formation of Fe3O4 seam at the oxide-steel interface. The present study offers an intriguing insight into the deformation behaviour of the tertiary oxide scale formed on steels, and may help with understanding the stress-aided oxidation effect of metal alloys

Effects of grain boundaries in oxide scale on tribological properties of nanoparticles lubrication

The characters of grain boundaries in oxide layers formed on substrates influence adhesion and friction behaviour, surface fracture and wear during high temperature steel processing. In this work, an electron backscattered diffraction (EBSD) analysis was conducted to investigate the role of surface grain boundary and orientation in magnetite (Fe3O4)/haematite (α-Fe2O3) scale during hot rolling, and further evaluate their effects on tribological properties of water-based nanoparticles lubrication. The results demonstrate that Fe3O4 (100) plane is strongly sensitive to the surface characteristics as the minimisation of surface energy. Coincident site lattice (CSL) boundaries in microstructure is in presence of Σ3 in the Fe3O4 and Σ13b in the Fe2O3 of the substrates subjected to a thickness reduction of 28% and cooling rate of 28 ° C/s. This is due in great part to the changes in crystal slip systems. These low-Σ CSL boundaries in oxide scale offer obstacles to the propagation of cracks, where some of nanoparticles collected would be trapped at the interface and thereby may cause high wear rates. A lubrication mechanism is proposed to explain the grain boundary effect on nanoparticles lubrication, and further to determine the dependence of frictional behaviour on surface energy, crystallographic preferred orientation (microtexture) and crystal structure. These results provide an intriguing new insight into the application of water-based lubricant with graphite nanoparticles

Effect of Deformation Parameters on Microstructure and Mechanical Properties of Internal Crack Healing in As-Cast 30Cr2Ni4MoV Steel

Crack defects seriously affected the quality of heavy forgings, which needed to be eliminated by forging process. In this study, the healing process of internal crack defects was studied under different deformation parameters. The internal crack was produced by drilling the sample of 30Cr2Ni4MoV steel and then compressing the sample with different deformation. The microstructure of the crack healing zone was observed using an optical microscope. Meanwhile, the static and dynamic mechanical properties of the crack healing zone were tested by room-temperature tensile tests and impact tests, respectively. The results showed that dynamic recrystallization (DRX) and grain growth were the main factors for internal crack healing. When the forging ratio (FR) was 1.5, the cracks at the corner of the void began to heal, which was caused by DRX. At FR 2.0, the DRX was completed and the center crack was completely healed. The tensile properties of crack healing zones were restored to more than 95% of the base material. As the FR increased to 2.2, the elongation increased slightly and the yield strength decreased slightly, which indicated that the grain growth played an important role in the plastic recovery and DRX played an important role in strength recovery. The dynamic mechanical properties of the crack healing zone gradually increased with the increase of deformation. Furthermore, the maximum value of impact toughness reached FR 2.0, and the recovery rate of impact toughness was above 96%. When the deformation continues to increase, the grains grew up after DRX, which made the impact energy decrease