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For advanced plasticity problems such as fracture prediction, the use of a non-associated flow rule as a constitutive model is effective to represent bifurcation phenomenon. In addition to this, to represent strong anisotropy observed in cold rolled sheets, the use of a non-associated flow rule model is essential because this can separate the deformation anisotropy and stress anisotropy. However, a sufficiently practical model has not been developed. In this study, experimental and analytical investigations on a function for the non-associated flow rule model proposed by the authors are presented.

To expand the application ranges of sandwich sheets from conventional 2D flat panel types to 3D complex shapes and simultaneously improve the specific bending stiffness, a novel topology optimization strategy that can optimize the bending stiffness while maintaining good formability was proposed. In the proposed approach, the density-based topology optimization was integrated with the multi-stage genetic algorithm (GA) to optimize the repeatable unit cell of the core structure of sandwich sheets. Two optimization schemes were adopted, in which one optimizes the formability and the other one optimizes the bending stiffness while fulfilling potential failure constraints. The failure constraints on core shear failure and face buckling were theoretically deduced to mathematically formulate the topology optimization problem, which was solved by the adaptive multi-stage GA to increase the possibility of generating physically meaningful and additively manufacturable topologies. For the experimental evaluations of mechanical properties and formability, the final optimal topologies under volume fraction constraints of 50% and 62.5% were additively manufactured using carbon fibre reinforced nylon. Comparing the sandwich topologies obtained by two optimization schemes, the bending stiffness of sandwich topologies with the core density of 50% and 62.5% are improved by 41.58% and 41.49%, while the energy absorption capabilities are improved by 13.60% and 29.40% respectively. L-bending and draw-bending tests indicate the improved formability of topologically optimized sandwich sheets. The proposed approach is capable of designing formable sandwich sheets with improved bending stiffness, which is expected to expand the application envelope of sandwich sheets with better mechanical properties.

The optimal structural hierarchy was introduced into the conventional pyramidal structure by integrating the homogenization-based topology optimization (HMTO) with elastically isotropic elementary lattices for further improvement of structural efficiency. The mechanical properties and elastic isotropy of representative truss–lattices composed of struts and plate–lattices consisting of closed-cell sheets were firstly evaluated, based on which the equivalent out-of-plane compression modulus of the hierarchical pyramidal structure was theoretically analysed and then compared with experimental and numerical results to systematically clarify the effects of lattice topology on the structural performance. Furthermore, the elementary lattice exhibiting the optimal structural efficiency and elastic isotropy was integrated with HMTO to optimize the out-of-plane compression properties including stiffness and energy absorption capability. The hierarchical pyramidal structure with optimal structural hierarchy achieves 4.8% and 28.2% higher compressive modulus over the conventional pyramidal structure and unoptimized hierarchical pyramidal structure, respectively. The energy absorption capability of optimized and unoptimized hierarchical pyramidal structures is 63.4% and 27.2% higher than that of conventional pyramidal structure without structural hierarchy, respectively. The results obtained from this study indicate that the structural hierarchy introduced via integration of isotropic SC–FCC plate–lattice with HMTO can effectively improve the structural efficiency of hierarchical pyramidal structures.

The static softening behavior of A5083 aluminum alloy was studied through two thermomechanical tests, namely double-pass compression test and stress relaxation test. Metadynamic recrystallization and the further conventional static recrystallization cannot achieve complete recrystallization, which means that in the stress relaxation test, the traditional method used to determine the recrystallized fraction is no longer applicable. Hence, a new method is proposed based on the sigmoidal relationship between the relaxation stress and the recrystallized fraction. The order of the effects of the forming parameters on the metadynamic recrystallization, from strong to weak, is as follows: strain rate, temperature, and first-pass strain. External stress plays a significant role in retarding metadynamic recrystallization, thereby amplifying the effects of the forming parameters on the metadynamic recrystallization. Interestingly, metadynamic recrystallization, which is considered to occur immediately, has an incubation time of approximately 1 s in the studied aluminum alloy. The evolution of the microhardness and microstructure studied through microhardness tests and electron backscatter diffraction confirmed these conclusions. In addition, the phenomena of stress hardening and yield stress drop, caused by strain aging, were observed only under special experimental conditions.

The application of sandwich sheets containing a three-dimensional core is limited due to low manufacturing efficiency and poor formability . Metal-based sandwich sheets, where thin metallic face sheets are used to sandwich and bond with a three-dimensional core fabricated by stamping an initially flat carbon fibre reinforced thermoplastic (CFRTP) sheet, are able to provide high specific stiffness with suitability for mass production. Aiming at secondary forming such sandwich sheets into three-dimensional shapes, cold and warm forming characteristics of sandwich sheets composed of various face sheets and a three-dimensional CFRTP core with different fibre lengths and volume fractions were investigated. The numerically predicted pure bending rigidity and out-of-plane shear modulus were converted into numerical three-point bending stiffness through theoretical formulas and compared with experimental values to clarify the mechanical properties of different sandwich sheets. A three-dimensional core was successfully fabricated by warm stamping ultrathin chopped carbon fibre tape reinforced thermoplastic (UTCTT) with carbon fibre volume fraction of 40%. Draw-bending demonstrates that formability of sandwich sheets can be improved by optimising material combinations and forming temperatures. Sandwich sheets composed of metallic face sheets and a short carbon fibre reinforced thermoplastic (SCFRTP) core can be easily cold formed, while those with a UTCTT core can be easily warm formed.

A precure–hot forming–postcure (P–HF–P) process, in which CFRP prepregs were firstly hot pressed to eliminate its interlayer voids and pre-cured followed by hot formed into 3D shapes and finally post-cured, was proposed for the rapid fabrication of 3D CFRP parts. The void fraction, flexural modulus and strength of different regions of 3D CFRP parts fabricated by P–HF–P and autoclave processes were evaluated. Then the overall axial compression and transverse bending properties of CFRP parts fabricated by different processes were experimentally and numerically investigated. The void fraction, flexural modulus and strength were improved by increasing the pre-curing time of P–HF–P process, and a void fraction of 2.5% and comparable flexural properties were achieved to the autoclave process. CFRP parts manufactured by the P–HF–P process with a pre-curing time of 10 min had comparable overall load-bearing and energy absorption capacities to those fabricated by autoclave process under axial compression and transverse bending. The comprehensive comparison of void fraction, flexural properties, and overall load-bearing capacity and energy absorption ability indicates that the P–HF–P process achieves a better balance between the high productivity and high quality of CFRP products than autoclave process.

An anisotropic plasticity model is developed based on the non-associated flow rule with anisotropic hardening. The model combines non-quadratic yield function and quadratic plastic potential function for orthogonal anisotropic sheet metals. The model is also expanded to properly reproduce the cyclic effect during forming processes. The simple formulations can contribute to cost saving in the parameter acquisition process and implementation. The developed model was implemented into the finite element code ABAQUS as a user material subroutine under a general three-dimensional condition. To evaluate the capability of the plasticity model, different loading conditions and prediction of the yield surface were considered. A multi-step rectangular cup drawing process with the AA5182-O and DP600 sheets including draw/re-draw effects was applied to evaluate the performance of capturing complex plastic behavior by finite element simulation. The results show that the anisotropic plasticity model is capable of describing the anisotropic behaviors including anisotropic hardening and cyclic hardening with high accuracy and efficiency.

The inhomogeneous quality of products manufactured by semisolid forming is mainly attributed from the phase segregation of semisolid metal slurry during forming. Phase segregation can be inhibited by lower forming temperature, higher strain rate, and lower stroke. However, the realization of net-shape forming with above parameters is quite difficult. In this study, a multi-stage thixoforging strategy including a partial melting, a fast first compression, a partial solidification, and a secondary compression was proposed to weaken phase segregation of thixoformed samples. A physical simulation of multi-stage thixoforging was conducted on commercial rolled Cr-V-Mo tool steel SKD11, using a multistage hot compression test machine. The microstructural evolution and forming behaviors of the SKD11 steel slurries in different stages of multi-stage thixoforging with various forming parameters were investigated experimentally. Out flow of liquid phase does not occur throughout the thixoforming, and can be inhibited effectively by partial solidification and subsequent secondary compression. SKD11 steel sample more homogenous microstructure and smoother surface was manufactured by multi-stage thixoforging including a fast first compression with a stroke of 4 mm and a strain rate of 2.0/s at 1280 °C, a partial solidification to 1240 °C with a cooling rate of 2 °C/s, and a secondary compression with a stroke of 2 mm and a strain rate of 0.1/s at 1240 °C.

Reheating and rapid cooling experiments, and semisolid compression tests were conducted on extruded Mg–8.20Gd–4.48Y–3.34Zn–0.36Zr alloy using a multistage hot compression test machine. Affected by reheating temperature, heating rate and isothermal holding time, dissolution of eutectic compounds and partial melting occurred during reheating, dynamic arrangement of alloying elements and phase transformation took place during subsequent rapid cooling. These microstructural behaviors not only changed the anisotropy in microstructural morphology of the extruded Mg–8.20Gd–4.48Y–3.34Zn–0.36Zr alloy, but also affected the anisotropy in forming properties of it. When this alloy was reheated to 580 °C with a heating rate of 20 °C/s and held isothermally for 20 s, semisolid slurry without anisotropy in microstructural morphology and forming properties, exhibiting a homogeneous spherical microstructure was obtained.

Fracture prediction in metal forming has captured attention because of its practical importance. Recently, demand for fracture prediction has grown to conduct an effective forming process design using numerical simulation; however, the increasing use of high-strength steels and anisotropic materials prevents accurate simulation in large strains in which fracture tend to occur. In this study, a fracture prediction framework based on the bifurcation theory is constructed. The core is a material model based on stress-rate dependency related with non-associate flow rule. This model is based on non-associated flow rule with arbitrary higher order yield function and plastic potential function for any anisotropic materials. And this formulation is combined with the stress-rate-dependency plastic constitutive equation, which is known as the Ito-Goya plastic constitutive equation, to construct a generalized plastic constitutive model in which non-normality and non-associativity are reasonably included. Then, by adopting the three-dimensional bifurcation theory, more accurate prediction of the initiation of shear band is realized, leading to general and reliable construction of forming limit diagram.

The demand for new processes to produce high strength parts, under appropriate cost and productivity, has grown with weight reduction and crash safety improvements in automobile design. The hot stamping processes of quenchable steel sheets potentially offer not only small forming load and high formability, but also high strength and no springback by die quenching. This paper aims to provide an overview of the state-of-the-art in such hot stamping processes, including quenchability, formability, heating and cooling approaches and lubrication. The paper also includes a description of the mechanism of formability and quenching, tailoring, analysis of hot stamping processes and applicability.

High temperature mechanical properties of Mg alloys could be improved effectively by adding Zr and rare earth (RE) elements, such as Gd and Y, in Mg matrix. In order to achieve the sufficient utilization of both the volume and properties Mg–Gd–Y–Zn–Zr alloys, semisolid forming (SSF) is one of the most potential methods to realize the near net shape manufacturing. To verify the feasibility of the SSF in manufacturing of Mg–Gd–Y–Zn–Zr alloy products, partial melting and backwards thixo-extrusion experiments of Mg–8.20Gd–4.48Y–3.34Zn–0.36Zr alloy were conducted in semisolid temperature range of it (520~580 °C). The microstructural evolution of this alloy during partial melting and backwards thixo-extrusion was studied experimentally. This alloy exhibited different microstructural morphologies and formability at different extrusion temperature. At lower semisolid temperature (520~560 °C), liquid phase with lower volume fraction cannot improve the ductility of this alloy effectively. At higher semisolid temperature (580~620 °C), handling and transferring of semisolid slurry became quite difficult, owing to the liquid phase with higher volume fraction. The occurrence of liquid segregation and plastic deformation of solid particles during thixo-extrusion at higher semisolid temperature resulted in inhomogeneous distribution of microstructure and mechanical properties of the sample.

Chain-die forming is a promising manufacturing technology that is emerging as an alternative to roll forming and stamping in fabricating Advanced High-Strength Steel (AHSS) products. The microstructure evolution is a critical factor for evaluating the severity of a fabrication process, especially the plastic deformation. This paper mainly attempts to understand the microstructural changes involved with the Chain-die forming process. Scanning Electron Microscopic (SEM) observation and Electron Backscatter Diffraction (EBSD) analysis were adopted to have a deep understanding on microstructure evolution. Microscopic results of the investigation show that there is almost no variation of grains, with respect to Kernel Average Misorientation (KAM) value and rotation of the grains, in the undeformed areas. Rotation of the grains is observed between inner edge and outer surface regions. The microscopic analysis also revealed that the KAM distribution shifts to higher values at the highly deformed region.

In this study, carbon fiber-reinforced plastic (CFRP)/Al laminates are made through autoclave cocuring. Three-point bending, stamping bending, and micromorphology analyses are conducted to study the failure of FMLs in the bending process and the influences of fiber direction, metal thickness ratio, and temperature on springback. Results show that the fiber direction exerts a great influence on the failure mode and springback of the laminates. Al alloy and CFRP are bent, and the influence of temperature on the springback of three different sheet is compared. The formability of CFRP is sensitive to temperature, and the springback rate varies by approximately 30% between room temperature and 150 °C. By contrast, the springback rate of Al alloy and CFRP/Al laminates changes by only 5% in such a temperature range. Orthogonal 45° CFRP/Al laminates exhibit good formability at room temperature, and the springback rate is approximately 3.2%. The change in springback rate is inevident below 150 °C, and the delamination between fiber and metal layers occurs near 200 °C. Surface modification of aluminum plates using coupling agents can improve the resistance of CFRP/Al to failure during bending.

During the self-piercing riveting process of carbon fiber reinforced polymer (CFRP) and aluminum sheets, the CFRP is penetrated by the rivet, which weaken the mechanical properties of the joint of CFRP and aluminum alloy sheets to a certain extent. To improve quality of the joint, this study proposes a post-curing self-piercing riveting (PC-SPR) method to join CFRP with aluminum alloy sheets. The mechanical properties and failure modes of the joints were studied through tensile shear tests and the effects of joint structure and CFRP thickness on joint quality were examined. The failure mode of the joint was analyzed by observing the microscopic appearance, and the damage mechanism of the joint was systematically discussed. Results showed that compared with regular self-piercing riveting (R-SPR) joints, PC-SPR joints had better strength.

In-depth understanding of the impact mechanism of nitrogen on tempering behavior of hot-working die steel is still limited. In present work, the microstructural evolution and mechanical property change of new nitrogen-alloyed Cr–Mo–V hot-working die steel during long-term tempering were investigated by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), eletron backscattered diffraction technique (EBSD) and 3D atom probe tomography (3DAP). The impact mechanism of nitrogen on tempering stability were discussed in detail. The results reveal that whether nitrogen is beneficial to the tempering stability of steel varies with quenching temperature. Trace nitrogen exerts a significant effect on the allowed quenching temperature and metastable M3C carbides, affecting the coarsening rate and transformation of M23C6 carbides during tempering process. Tempering stability was improved by nitrogen mainly by enhancing precipitation hardening and grain refinement strengthening, which account for about 70% of total yield strength. Improving effect of nitrogen in precipitation hardening is more distinct with the increase of tempering time. These results are helpful for understanding the mechanisms of nitrogen in steels worked at high temperatures.

The synergy of additive manufacturing (AM) with topology optimization has become a useful method for developing ultralight, ultrastiff structures with high energy absorption capability. To improve the weight-specific stiffness and energy absorption capability of the conventional dome commonly used as the core of sandwich sheets, a new concept of filling the solid part of the dome with stretch-dominated microlattices is proposed. The optimal density distribution of microlattices is obtained by integrating the homogenization-based topology optimization method with the lattice structure. The compressive and bending stiffnesses of the optimized variable-density microlattice domes are demonstrated to be 41.8% and 33.7% higher than those of the conventional solid domes, while the energy absorption of the microlattice dome during compression and three-point bending is increased by 297.5% and 85%, respectively. Investigation of the cell size effect on the mechanical properties of the microlattice dome reveals that a larger cell size contributes more to the weight-specific stiffness and energy absorption capability at a given overall volume fraction constraint. The topology optimization and construction methods described in this paper are universal and can be used for the further development of ultralight, ultrastiff structures with arbitrary macro shapes with microlattices as constituent units.

For the manufacture of good quality strips by rolling processes, the bending residual stress of the strip is one of the most important qualities to be controlled. Most reports on strip bending behavior have focused on thick plates produced under batch rolling conditions [1, 2], and few reports have examined continuous rolling of thin plates. In this report, we conducted a single-drive rolling test with a strip having the thickness of 0.23mm and a 2Hi test mill with work rolls 410mm in diameter. We also calculated the pressure distribution and warping curvature. The model used here was based on the Orowan model constructed by Morimoto and Yanagimoto [3]. In this calculation, the roll bite was separated into 3 sections, i.e., forward slip region, backward slip region and cross shear region. In the calculation results, the pressure distribution showed the existence of a pressure well in the cross shear region, as also reported by Zorowski et al. [4] The curvature in the calculation result increased as the reduction ratio increased up to 10%, but decreased with increasing reduction ratios larger than 10%. This tendency was the same as the measured curvature in the experiment, and was considered to be caused by the moment by friction force at the cross shear region and also the aspect ratio of the cross shear region.

Press forming technology for carbon-fiber-reinforced plastic (CFRP) sheets consisting of thermosetting resin and continuous fibers is required to manufacture lightweight structures. It is considered that the formability of CFRP sheets is less than that of metallic sheets. Formability tests for metallic sheets can also be applied to compare the formability of CFRP sheets. There are four types of formability for metallic sheets; bendability, deep drawability, stretchability, and stretch flangeability. Bending and stretching tests for CFRP sheets under a suitable forming temperature and means of assisting the deformation of the sheets have been developed. The stretch flangeability of CFRP sheets should be low because cracks in the resin around the edge tend to develop under smaller strain. In this study, the bore-expanding ratio was obtained in a bore-expanding test to determine the stretch flangeability of laminated CFRP structures.

The deformation of carbon-fiber-reinforced plastic (CFRP) sheets consisting of a thermosetting resin and continuous fibers has been investigated. The bending of CFRP sheets was achieved under a suitable forming temperature and strain path. Formability indexes and a forming limit diagram (FLD) are indispensable data for showing the process window of CFRP sheets. There are four formability indexes: bendability, deep drawability, stretchability, and stretch-flangeability. Bendability and deep drawability can be evaluated by conducting a stretch-bending test, and stretchability can be evaluated by conducting an Erichsen cupping test. If the process window can be predicted, the range of applications using CFRP can be expanded. In this study, the Erichsen index of CFRP sheets indicates the stretchability of laminated CFRP structures.

Friction stir welding (FSW) was applied to a low carbon alloyed steel in order to stabilize the austenite phase which can effectively maintain a preferable toughness. A Cr–Mo steel sheet (0.20 wt.%C–1.07%Cr–0.16%Mo–0.24%Si–0.61%Mn–bal. Fe) with a ferrite pearlite structure was friction stir welded under the conditions in which the sample was reheated above the A3 temperature at the maximum. The microstructure observations in the stir zone clarified martensite with several area fractions of retained austenite and elongated ferrite. The retained austenite provides a high ductility with a high strength in the stir zone. In order to clarify the formation mechanism of the austenite, compression tests were conducted at various strain rates up to 10/s using an ultrahigh-speed compression testing machine. When the sample was compressed at the high strain rate, the elongated ferrite grains and retained austenite were formed. This microstructure was similar to the microstructure in the FSW stir zone, suggesting that the efficient accumulation of plastic strain in the austenite during the FSW plays an important role in obtaining the retained austenite. Keywords: Friction stir welding, Steel, Strain rate, Phase transformation

The stamping of an ultra-thin stainless steel sheet into a wave shape for a finless heat exchanger was investigated. As an alternative to fins made by the extrusion or drawing, a bidirectionally corrugated shape is advantageous because of its higher efficiency in heat exchange with smaller resistance to an ambient air flow. A greater wave height is advantageous, but is suppressed by fracture during stamping. A new stamping method was developed to realize a high-efficiency heat exchanger using an ultra-thin stainless steel sheet with an optimized corrugated shape in terms of the plan-view pattern and cross-sectional profile.

In the case of complex forming process that receives a secondary loading after the primary loading, it is necessary to appropriately represent the work-hardening state according to the forming history. Namely, it is necessary to accurately model complex forming process including reversal loading (Bauschinger effect) and orthogonal loading (cross-hardening). In this study, a composite anisotropic hardening expression based on the crystallographic structure using the finite element polycrystal model is proposed. Numerical investigations are conducted to consider the effectiveness of the proposed model. In which, an alternation rate is introduced to capture the activity of the slip systems to support the idea behind the proposed model. In addition, flow curves of the secondary loading are produced by the proposed model, which is compared with the conventional model.

For the purpose of grain refinement and improvement of the hot formability of duplex stainless steel, a new concept of the thermomechanical processing method using the austenite phase transformation from the δ ferrite phase in the hot working temperature range was proposed. The supercooled δ ferrite phase is generated by rapid cooling immediately before hot working, and crystal grains are refined by the austenite transformation induced by hot working immediately after rapid cooling. Furthermore, since the new thermomechanical processing method is characterized by a large amount of soft δ ferrite phase during hot working, reduction of hot flow stress and improvement of hot ductility are possible in addition to grain refinement. The material used here was 25 % Cr duplex stainless steel, and the temperature history was controlled by combining induction heating and nitrogen gas cooling. It was confirmed that the δ ferrite phase was obtained as the parent phase by initial heating at 1320 °C, and a supercooled δ ferrite phase was generated by rapid cooling at 30.0 °C/s from the initial heating temperature to the hot working temperature of 1000 ℃. When uniaxial compression of 60 % at strain rates of 0.1, 1.0 and 10.0 s −1 was applied to the supercooled δ ferrite phase after cooling to 1000 ℃, nucleation of austenite grains was induced by the degree of supercooling and compressive strain, and as a result, the microstructure was successfully refined by strain-induced fine austenite grains. The grain diameter of the austenite grains obtained by strain-induced transformation was several μm. The flow stress under thermomechanical processing, which succeeded in microstructure refinement, was much lower than that under the condition simulating the conventional process. The hot ductility investigated in the uniaxial tensile test was also greatly improved under thermomechanical processing. Finally, the results of a detailed crystal orientation analysis revealed that the nucleated fine austenite grains obtained by strain-induced transformation have a K–S relationship with the supercooled δ-ferrite parent phase.

Hot compression tests of A5083 aluminum alloys with extruded and homogenized initial microstructures were carried out at varying temperatures (350 to 450 °C) and strain rates (0.1 to 10/s). The effects owing to nonuniform temperature and strain distributions caused by deformation were compensated by inverse analysis to determine the flow curves. The obtained flow curves with a homogenized initial microstructure were lower than those with an extruded initial microstructure. Constitutive descriptions were obtained to study the dynamic kinetics during compression, and comparisons between the predicted results from constitutive equations and the experimental results from associate microstructures verified their accuracy. Electron backscatter diffraction (EBSD) was utilized for observing microstructures. The characteristics of continuous dynamic recrystallization, particle-stimulated dynamic recrystallization and conventional dynamic recrystallization were confirmed. The dynamic recrystallization process with a homogenized initial microstructure is slower than that with an extruded initial microstructure, owing to the different amounts of subgrain structures during the initial deformation stage, which can affect the speed of the continuous dynamic recrystallization process. Microhardness tests were conducted to study the connection between microstructure and mechanical property. The microhardness after deformation with an extruded initial microstructure are higher than those with a homogenized initial microstructure.

An aluminum alloy (A6061) reinforced with graphene nanosheets (GNSs) was successfully fabricated by ultrasonic processing, high-frequency induction heat sintering (HFIHS), and hot extrusion. Harmful aluminum carbide (Al4C3) was not formed during HFIHS process as well as GNS particles were found to be able to stimulate recrystallization, restrict grain growth, and disturb the preferential texture in the present work. Enhancements in compressive strength of up to 50.4%, Vickers hardness of 13.3% as well as a 21.7% reduction in the friction coefficient along with a 17.2% reduction in the wear rate compared with those of as-extruded A6061 were measured. These improvements were due to the homogeneous dispersion of 0.25 wt% GNSs in the matrix. In addition, the yield strength predicted using modified model was in good agreement with the experimental results reported in this study. However, deterioration of the mechanical properties of the composites and a discrepancy between the theoretical prediction and experimental values occurred with the addition of 0.5 wt% GNSs owing to GNS agglomeration. This study demonstrated that the incorporation of an appropriate amount of GNSs can enhance the overall properties of a metal matrix, opening up an innovative design concept for fabricating bulk metal matrix composites (MMCs).

The application of CFRP (carbon fiber reinforced plastic) parts in the automotive industry is limited by their labor-intensive and time-consuming manufacturing processes. Moreover, the strong demand for long products, such as components with a length of 25 m used in high-speed railroad vehicles, requires the manufacturing of long CFRP sheets, which are extremely difficult to produce using the conventional autoclave process. To achieve the rapid production of long CFRP products, a method of continuously manufacturing CFRP sheets by rolling is proposed in this study, and the effects of the preheating and curing times as well as the gap between rollers on the properties of the produced CFRP sheets such as void fraction, thickness, strength and formability are investigated. The CFRP sheets produced by the newly proposed rolling process have comparable performance characteristics such as void fraction, strength, formability, energy absorption and load tolerance to those of the CFRP sheets fabricated by the autoclave process. Owing to its much higher manufacturing efficiency, the rolling process is expected to replace the conventional time-consuming autoclave process for the fabrication of long CFRP sheets for a wider range of engineering applications.

An anisotropic constitutive model based on the non-associated flow rule that is combined with non-quadratic and quadratic functions was developed for orthotropic anisotropic sheet metals. The non-quadratic Barlat's YLD91 function was applied for the description of the anisotropy in the yield stresses, and the classical quadratic Hill48 function was adopted to describe the anisotropy in the plastic deformation. A continuous scheme for capturing the anisotropic hardening based on the implicit YLD91 function was proposed for higher modeling accuracy. The anisotropic parameters can be obtained from three directional uniaxial tensile tests and a hydraulic bulge test. The developed model can be applied under a general three-dimensional condition. The developed model was implemented into the finite element code ABAQUS as a user material subroutine (UMAT). To evaluate the capability of the developed model, directional uniaxial tension and prediction of the yield surface were considered, and a circular hole expansion process with the JSH590R sheet were simulated using different material models. A suitable static-implicit analysis and solid elements were applied. The comparison between the experimental and simulation results indicates that the modeling accuracy can be improved by applying the developed model. Furthermore, the simple formulations can also contribute to cost saving in the parameter acquisition process and computation. It is concluded that the developed anisotropic model can be used as an alternative and user-friendly method in solving the common industrial problems with large plastic deformation.

Bendable metal-based composite sheets with a truncated dome core made of CFRTP (carbon fibre reinforced thermoplastics) were developed to expand the range of applications and improve the mechanical properties of sandwich structures. The newly proposed truncated dome core structure was composed of a periodic array of domes which were introduced into an initially flat CFRTP sheet through stamping. Theoretical analyses were conducted to determine the conditions required for successfully forming sandwich sheets into curved shapes. The flexural properties and formability of sandwich sheets were tested experimentally. The numerical simulation shows that the optimal relative density of the truncated dome core is 0.22. Experimental results of formability tests agree well with the theoretical predictions, which demonstrates the validity of the theoretical models. Sandwich sheets with both A2017P and SUS304 face sheets of a thickness of 0.5 mm can be bent without any failure at a bending radius of 60 mm.

Using a multistage hot compression test machine, reheating experiments and semisolid compression tests were conducted on two commercial rolled Cr–V–Mo tool steels, SKD11 and SKD61. Austenization, grain growth, carbide dissolution, and partial melting took place during the reheating of the tool steels, and resulting in spherical semisolid slurries at certain temperatures (1300 °C for SKD11, 1405 °C for SKD61). The microstructural evolution of SKD11 and SKD61 tool steels during reheating and rapid cooling was found to be different owing to their different alloying element contents and the different distributions and morphologies of the carbides inside them. The forming characteristics of the two tool steels in the semisolid state were discussed on the basis of the results of compression tests.

A new method for designing carbon-fiber-reinforced plastic (CFRP) sheets with a suitable ply structure for stamping is proposed. This method combines a generic algorithm with a three-dimensional finite element method (FEM) to reproduce a layered structure by homogenizing the fiber structure with elastic-plastic anisotropy of each layer. The maximum strain is used as a fracture index to evaluate the severity of sheet deformation under stamping. The ply structure of the CFRP is optimized for elliptic cup drawing, and the optimized ply structure is validated experimentally. Through the experimental validation, it is proven that the proposed method gives acceptable results for the optimization of the ply structure of thermosetting CFRP sheets for cold/warm stamping.

The forming processes at room temperature and under a warm condition have been investigated for carbon-fiber-reinforced plastic (CFRP) sheets consisting of thermosetting resin and continuous fibers used for mass production. While CFRPs consisting of thermosetting resin have the advantage of high strength, to subject them to press forming, in contrast to carbon-fiber-reinforced thermoplastics (CFRTPs), which consist of thermoplastic resin. When CFRP sheets are formed into the desired shape through plastic deformation, a higher-strength structural material easily applicable to mass production is obtained. To improve the formability of thermosetting CFRP sheets while retaining their strength, a suitable structure allowing plastic deformation under warm condition is proposed. The tensile stress obtained by a tensile test and the bending properties obtained by a stretch-bending test indicate the strength and formability, respectively. A stretch-bending test is a bending test in which a tensile load is placed on a sheet, and it has the characteristics of a bending test and a deep drawing test. A suitable structure containing prepreg layers to allow plastic deformation based on the relationship between the bending load and the results of specimen observations is revealed.

A heavy-reduction controlled rolling process with approximately 75% thickness reduction was carried out to investigate the microstructural evolution including texture development, focusing on the formation of a bimodal structure of 0.2% carbon steel with heating temperatures of 700, 800, 900, and 1000 °C. Upon increasing the heating temperature from 700 to 900 °C, the microstructure was refined and precipitates such as Fe 3 C were uniformly distributed throughout the microstructure. For the microstructures control-rolled at heating temperatures of 900 and 1000 °C with average ferrite grain sizes of 1.34 and 1.63 μm, respectively, a bimodal structure could be observed by scanning electron microscopy (SEM), which was very similar to the result of a plane-strain compression (PSC) test. Moreover, the 900 and 1000 °C-heated specimens had less well developed textures primarily consisting of {113}–{4 4 11}〈110〉 and {332}〈113〉 components, which usually developed by the transformation (γ→α), and the 1000 °C-heated specimen exhibited various textures and a low intensity of the {100}〈011〉 component, which was generally transformed from the {100}〈001〉 component of the recrystallized austenite.

A growing number of studies suggest that the accumulation of unwanted elements is a growing problem in all recycled material streams. Thus, the separation of tramp elements from aluminium alloy scrap is very important in the aluminium recycling process. In this paper, a new technique of backward extrusion in the semisolid state is reported for separating the tramp elements from aluminium alloy scrap and obtaining high-purity aluminium easily and quickly. In this process, partial solidification is adopted to condense tramp elements in the liquid phase on the grain boundary. In experimental trials, four aluminium alloys were selected: cast aluminium alloy (AC4C), two kinds of wrought aluminium alloy (A7N01, A7075) and aluminium beverage can scraps. From the results of macro- and optical microscopic analysis, Rockwell hardness testing and electron probe micro-analyser (EPMA) analysis, it was confirmed that the backward extrusion in the semisolid state could separate the tramp elements from the aluminium alloy scrap easily and high-purity aluminium was obtained.

New metal matrix composite (MMC) manufacturing process to produce the compound material of carbon nanotube (CNT) and aluminum is proposed. This process is capable of MMC manufacturing with excellent electrical and mechanical properties, by controlling powder compacting stress and the temperature of the hot extrusion to integrate of CNT and Al powder. The crystalline of CNT in the MMC was systematically investigated, and it was confirmed that the crystalline of CNT was maintained without receiving the influence of heat by the hot extrusion. The new MMC manufacturing process might be an ideal process for an electric conductivity increase.

The different forming behaviors of the solid and liquid phases in semisolid metal slurry during deformation result in products with inhomogeneous quality. A mechanical servo press with the capability of multistage compression was employed to forge A6061 aluminum alloy in the semisolid state. A time-dependent rheoforging strategy including mechanical stirring, a fast first compression, short holding, and a secondary compression was designed to improve the homogeneity of rheoforged samples. The distributions of the microstructure and mechanical properties, such as the solid fraction, hardness, and deformation resistance, of samples manufactured under various experimental conditions were investigated. When the stirred semisolid A6061 slurry was forged in the temperature range from 625 to 628 °C with a short holding time of 4 s and the upper die preheated to 300 °C, samples with a homogeneous microstructure and mechanical properties were manufactured. The homogeneity of rheoforged samples was attributed to the controllable free motion capability of the mechanical servo press and the adjustable fluidity and viscosity of the semisolid slurry.

Adhesive–embossing hybrid joining process was applied to A2017P and three types of glass-fiber-reinforced plastic (GFRP) thin sheets. Optical microscopy shows that a sound A2017P–thermosetting GFRP hybrid joint without crack/delamination in the composite or adhesive failure can be produced by optimizing adhesive thickness, embossing stroke and embossing temperature. The results of tensile shear test indicate that the optimally hybrid-bonded A2017P–GFRP joint exhibits improved load carrying capability, slip displacement and better energy absorbing characteristics than the adhesively bonded joint when subjected to tensile loading. This investigation shows that the adhesive–embossing hybrid joining process is a competitive alternative joining method for the fabrication of ultra lightweight thermosetting GFRP-metal hybrid structures and has great potential for wider applications, which is attributed to its benefits in terms of joining properties, operation simplicity, weight-cost effectiveness and recyclability.

In the seamless pipe rolling process, the pipe wall thickness is largely determined at the mandrel mill or plug mill. It is possible to obtain the target thickness at these mills by defining the gap of a grooved roll and an inside tool such as a plug. However, the thickness of the free deformation part, which is not in contact with the roll and tool, had generally been estimated by experimental techniques. Although a number of analytical studies of mandrel mill rolling had been reported, few reports had examined plug mill rolling. Therefore, in this research, a finite element analysis model for plug mill rolling was developed by extending the rigid plasticity finite element model "Computational Rolling Mill (CORMILL)." Good agreement between the calculated results and experimental results was obtained for the wall thickness, and it was found that the thickness of the flange part decreases with reduction of the wall thickness at the grooved bottom. These results suggested that the wall thickness distribution of rolled pipes can be controlled by using a suitable inside tool and roll shape in each rolling pass, and the necessary shapes can be obtained by using the newly-developed model.

A compression test simulating heavy-reduction single-pass rolling was conducted to investigate the microstructural evolution based on the formation of a bimodal structure and the mechanical properties of 0.01% and 0.1% carbon steels and niobium steel. When thermomechanical processing was conducted near and above the critical transformation temperature ( A c 3 ), microstructures of all steels were significantly refined and consisted of equiaxed grains without elongated grains. Nevertheless, these microstructures showed weak or no formation of the bimodal structure or coarse grains with decreasing carbon content, while they showed bimodal structure formation when 0.2% carbon steel was used in our previous research. The average grain size of Nb steel was about 2 μm and its microstructure was uniformly refined. These may be attributed to a decrease in the number of nucleation sites with decreasing carbon content in low-carbon steels and the occurrence of nucleation at grain boundaries as well as in grain interiors in Nb steel during processing. Mechanical properties of all steels deformed above the critical transformation temperature exhibited high performance characteristics with superior strength and marked elongation. Their fractographs indicated ductile fracture, which was revealed by SEM observation after a tensile test.

T.M.C.P.(Thermo Mechanical Control Processing) has been widely used to improveplastic formability in steel strips. We have produced interstitial free steel(IF steel) strips and ferriticstainless-steel strips through T.M.C.P. rolling method. Optimizing conditions of hot rolling, hotrolled annealing, cold rolling and cold rolled annealing, we developed texture prediction model. Wecan predict rolling texture accurately using the conventional Taylor model. Moreover, we preciselypredict recrystallization texture classifying the total number of microscopic slips which arecalculated using the Taylor model. We consider that these calculated results provednucleation-oriented model and two types of recrystallization and grain growth mechanisms exit inour studies. One mechanism is that grains which had the small total number of microscopic slips arepreferred orientation for the hot rolled and annealed ferritic stainless-steel strip. The othermechanism is that grains which had the high total number of microscopic slips are preferredorientation for the cold rolled and annealed IF steel strip.

The material genome of type 316 austenitic stainless steel is presented. The material genome is a set of constitutive equations which describes the microstructure evolution during hot forming. Single- and double-compression tests at temperatures of 950–1150°C and with strain rates of 0.01–20 s−1 were performed to obtain the kinetics of dynamic and static events. Inverse analysis, which couples a thermomechanical finite element analysis with experimental data, is used to obtain the flow curves. It compensates the effect of inhomogeneous distributions of deformation and temperature during the compression tests. The sine-hyperbolic law, which relates the flow stress and the Zener–Hollomon parameter, is used to validate the accuracy of the solution. Regression analysis is applied on the coefficients of the flow curves in order to obtain the parameters of the constitutive equations. Microstructure investigations are used to demonstrate the validity of the newly obtained material genome.

The conventional route for tool steel manufacturing consumes large amounts of energy and time and results in a long process chain for the manufacture of products. Environmental consciousness is fuelling the development of an improved route with a shorter process chain and lower energy consumption that can replace the conventional one. An energy-efficient process route for manufacturing products with high quality was proposed based on recrystallization and partial melting (RAP) technology. To verify the feasibility of the RAP-based route, the effects of predeformation, partial melting, and post heat treatments on the microstructure characteristics and mechanical properties of cast Cr-V-Mo steel were studied experimentally. During the RAP process, plastic deformation, recrystallization, austenization, grain growth, and partial melting occurred. When the RAP processed specimen was quenched from 1050 o C after isothermal holding for 480 s and then tempered twice at 560 o C for 2 h, microstructural evolution occurred in both former solid-phase and liquid-phase regions and caused a good combination of mechanical properties.