Optimization of Thick 22MnB5 Sheet Steel Part Performance through Laser Tempering

Evaluation of ductile tearing resistance of an interstitial free steel sheet using SENT specimens

The essential work of fracture methd (EWF) to evaluate the fracture toughness of ductile materials in plane stress with prevalent gross yielding conditions was originally developed by the Cotterell‐Mai research group in Sydney University more than ten years ago. Since then, the EWF method has been proven independently by many researches to be a valid tool for a range ofductile metals, polymers, paper sheets and fiorous composites. The current interest in the technical community of the plastics industry is to extend the EWF methodology to high‐rate impact testing of polymers and their blends and to determine the impact specific essential work of fracture. Since the literatures related to the applicability of this mehodology under dynamic loading conditions appear controversial, our purpose in this work is to clarify under what conditions the impact EWF method is applicabe. The EWF methodology was applied to the energy impact data obtained on two PP copolymers and one ABS polymer at different specimen thickness and geometry. The results showed that the EWF method can be applied to high‐rate testing provided the ligament is fully yielded and the plastic zone is scaled with the square of the ligament length. When these conditions are fully satisfied, the impact specific EWF is a material constant independent of specimen geometry for a given sheet thickness in plane stress; and it is also invariant with specimen thickness when plane strain conditions are met.

Springback behaviour and quenchability in hot stamping of thick sheets

Ultralow carbon interstitial free (IF) steel was severely deformed up to a strain of 5.6 by the Accumulative Roll-bonding (ARB) process at 773 K. Crystallographic analysis by electron back-scattering diffraction (EBSD) technique in a field-emission type scanning electron microscope (FE-SEM) was carried out for the ARB processed IF steel throughout thickness of the sheet. Microstructural parameters, such as grain size, grain boundary misorientation and crystal orientation, through thickness of the ARB processed specimen were quantitatively clarified by the EBSD analysis. The ARB processed material was homogeneously filled with the lamellar or pancake-shaped ultrafine grains whose mean grain thickness were about 200–300 nm. More than 80% of the boundaries surrounding the ultrafine grains were high-angle grain boundaries. The ARB processed sheet had unique and complex textural distribution through thickness. The region near the thickness center has the conventional but quite weak rolling texture mainly composed of 〈110〉//RD and 〈111〉//ND. On the other hand, the surface region had the sharp shear texture, ND//〈110〉. Such a textural distribution is due to the redundant shear strain induced by high-friction between the sheet and roll during rolling. The correspondence between the textural and microstructural distribution and the shear strain distribution throughout thickness of the sheet was discussed.

Springback and fracture in v-die air bending of thick stainless steel sheets

Identification of mechanical responses of steel sheets under non-proportional loadings using dislocation-density based crystal plasticity model

Weakening of thick steel plates by laser radiation for the removal of hazardous substances

The ductile-brittle transition behaviour of organo modified montmorillonite-based Poly(lactic acid) films (PLA/o-MMT) was analysed using the Essential Work of Fracture (EWF) methodology, Small Punch Tests (SPT) and Enthalpy relaxation analysis. While the EWF methodology could only be applied successfully to de-aged samples, small punch test (SPT) was revealed as more effective for a mechanical characterization during the transient behaviour from duc- tile to brittle. According to differential scanning calorimetry (DSC) results, physical aging at 30°C of PLA/o-MMT samples exhibited slower enthalpy relaxation kinetics as compared to the pristine polymer. Although all samples exhibited an equiv- alent thermodynamic state after being stored one week at 30°C, significant differences were observed in the mechanical performances. These changes could be attributed to the toughening mechanisms promoted by o-MMT.

A theoretical crystal plasticity model to predict mechanical responses of ultra-thin (<0.1 mm thick) sheet metal under non-proportional loading, which are difficult to measure experimentally due to premature buckling in simple shear or compression-tension test, was developed. In the model, three different dislocation density components, namely, forward, reverse and latent dislocations, were incorporated in the crystal plasticity model. The model was applied for 100 μm thick ultra-thin ferritic stainless steel sheet to predict mechanical responses under two-step tension, and the predicted results were compared with the experimental data.

Summary This paper deals with the resistance spot weldability of steel to aluminium alloy using an intermediate layer of aluminium clad steel. Five types of clad sheet with various steel/aluminium thickness ratios were produced by hot rolling. The mechanical properties of the clad sheet changed with the thickness ratio and ranged between those of steel and:those of aluminium sheet. The peel strength of the steel/aluminium interfaces was greater than 25 N/mm. Materials used in spot welding were 0.8 mm thick EDDQ steel sheet, three types of 1.0 mm thick aluminium alloy sheet and the clad sheet mentioned above. Spot‐weldability, including suitable welding current, nugget diameter, tensile shear strength and thickness of the intermetallic compound layer formed at the interface of the clad sheets, changed with the thickness ratio of the clad sheet. From these results, it was concluded that spot‐weldability was affected by the thickness ratio of the clad sheets. Spot‐weldability was also affected by the alloyin...

Recent trends in the distribution of electrical energy through medium- and low-voltage grids, involving a variety of sources and smart infrastructures, call for extensive use of medium frequency transformers, as required for conversion steps and bidirectional power transfers. The employed grain-oriented (GO) cores are subjected to kHz frequencies and harmonics-rich voltages. These are scarcely assessed working regimes, regarding both loss behavior and dynamics of the domain structure. We perform in this work a thorough investigation on the energy loss dependence on frequency f (DC – 10 kHz) and peak polarization Jp (0.25 T – 1.7 T) of high-permeability 0.29 mm thick GO steel sheets, combined with the magneto-optical Kerr analysis of the dynamics of the domain walls and the evolution of the domain structure in well-oriented grains. The predicting model starts with the determination of the induction profile across the sheet thickness at any instant of time, according to the Maxwell’s diffusion equation, which is applied using the experimental normal/anhysteretic curves as magnetic constitutive equations. The classical energy loss component Wcl is calculated versus f and Jp, together with the evolution of the hysteresis loss Wh. This, although increasing with f, is observed to provide negligible contribution in the kHz range. The Kerr images show that the regular antiparallel domain wall (dw) structure is initially preserved under increasing f, at the cost of bowing and dw densification, while the excess loss Wexc follows a regular power law. However, at sufficiently high f and Jp values, the dws meet and annihilate at the surface, while remaining stuck as cylindrical domains at the sheet midplane. It turns out that in the high (f, Jp) corner the magnetization process occurs by penetration towards the midplane of extended dws parallel to the sheet surface, with Wexc and Wh dwarfed by the classical loss component.

Based on elastic stress and strain states after forming and joining processes, single and assembled parts show deviations regarding their dimensional accuracy. Therefore an analysis of selected influencing factors and their influence on the dimensional accuracy of assembled parts is performed in this paper. In this article a novel approach is presented that characterizes the impact of three geometrical shapes (convex/concave/straight) and different sheet thicknesses on the dimensional accuracy along a linked forming and joining process chain. The process chain consists of a deep drawing and a clinching process. Depending on sheet thickness, material and geometrical shape, the dimensional accuracy of single parts and joined assemblies varies. For the single parts the geometry of the specimen S-rail is used. Several types of assemblies are used for the proposed approach combining this specimen with a plane sheet or a second S-rail. The FEM-tools LS-DYNA and Abaqus, are used to demonstrate this approach. Simulations and experiments with aluminum alloy 6014, mild steel CR3 and sheet thicknesses of 0.7, 1.0 and 2.0 mm are conducted for single and assembled parts. In summary, a significant improvement of the dimensional accuracy of an S-rail assembly is demonstrated using two non-dimensional accurate single parts. Future work will be to analyze frequently occurring part segmentations for the joining technologies and to optimize material mix and sheet thicknesses in order to improve deviations of the assembly to the nominal CAD geometry.

Bending process is an important process in the metal sheet forming in many industries. The main problem of the bending process is the spring-back phenomenon after removing the punch. This research aims the investigation on effect of residual stress on springback behavior of sheet metal in U bending process. The corner setting technique and bottoming process were designed for experiments. The corner setting technique and bottoming has reduced the thickness in bending area to 5, 10, 15 and 20 percent of the original sheet thickness. Clearance between punch and die of both processes was equal to same the thickness. The residual stress value and springback phenomenal were investigated by commercial program code DEFORM 2D which was able to analyze the effect stress and force in bending area. Electrolytic zinc coated carbon steel grade JIS; SECC, JIS; 440 and JIS; 590 which having the thickness of 1 mm were employed as the workpiece material for all experiments. The result of three materials in conventional U bending die shows larger spring back than the corner setting technique and bottoming process. Moreover, the corner setting technique reduces spring back value in bending process but requires high bending force. Corner setting technique and bottoming process at 15% and 20% shows that the spring go of all parts. The FEM simulation results explained the effect of residual stress to springback phenomenal. Comparisons between experimental and finite element method results were also performed.

In order to investigate the perforation corrosion resistance of Zn-Ni alloy electroplated steel sheets in actual usage for automobiles, a pair of rear doors which were made from Zn-Ni alloy electroplated steel sheets and cold-rolled steel sheets were assembled for an automobile running test in Okinawa for 5 years. After 2.5 years, perforation corrosion penetrated an outer rear door of 0.6mm thick cold-rolled steel sheet. After 5 years, doors were deassembled and perforation corrosion was investigated. In the Zn-Ni coated door, corrosion occurred only at the hem flanges and the maximum corrosion depth was 0.05 mm. Granted that the Zn-Ni coating entirely loses its protection of steel and the perforation corrosion rate, hereafter, is the same as that of cold-rolled steel, it is assumed that the perforation corrosion should, eventually, penetrate a 0.6mm thick Zn-Ni coated outer panel in 7 years.

Dynamic laser piercing of thick section metals