Rolling Stress Research Articles

Effect of Hot-rolling Deformation on Microstructure and Mechanical Properties of Nd2Fe14Bp/Al-5Co-0.4Sm Composites

Nd2Fe14Bp/Al-5Co-0.4Sm composites were prepared via microwave sintering and hot rolling. The effects of hot-rolling deformation on the microstructure and mechanical properties of Nd2Fe14Bp/Al-5Co-0.4Sm composites were studied. The results showed that the internal porosity of the composites significantly decreased when the hot-rolling deformation rate was 45%. The Nd2Fe14B particles were broken into fine particles under rolling stress. Consequently, the particles were uniformly distributed. Moreover, numerous high-density dislocations were observed around the particles, which improved the strength and toughness of the material. When the deformation rate was 45%, the micro-nano hardness and elastic modulus of the interface of the composites were 3.6 and 91 GPa, respectively. The interfacial deformation resistance of the composites was significantly higher than that of the composites before rolling. The tensile strength of Nd2Fe14Bp/Al-5Co-0.4Sm composites increased as the deformation rate increased, whereas the elongation gradually decreased. Furthermore, when the deformation rate was 45%, the tensile strength and elongation of the composites were 161 MPa and 6.5%, respectively. The tensile strength was 14.2% higher than that of the unrolled sample.

Advanced multi-scale analysis of segregation mechanisms in twin-roll casting of Al-Cu-Li alloys

In this paper, a detailed analysis of the rheological behaviour and segregation mechanisms within twin-roll casting (TRC) processes for 2060 Al-Cu-Li alloys is presented. Building on previous research where fixed roll gaps limited the adjustability of cast-rolling speed, this study expands the scope by adjusting roll gaps from 3 mm (TRC-3), to 6 mm (TRC-6), to 10 mm (TRC-10). This approach yields three typical process ranges with gradually increasing roll gaps and a wide range of decreasing cast-rolling speeds, allowing us to investigate the inherent nature of segregation and identify conditions conducive to segregation-free processing. A significant contribution of this study is the development of a novel multi-scale simulation model that integrates the thermal, flow, mechanical, solute and phase fields. This advanced simulation framework enhances our understanding of TRC processes and aids in exploring the interplay between the various factors affecting alloy fabrication. This study identified two primary stress-induced inverse segregation mechanisms: the reflux of the semi-solid phase due to rolling stress and expansion of the solidifying shell under shearing stress. Using these insights, a low-stress, low-segregation process, termed TRC-6, was established, which showed notable improvements in the mechanical properties. Specifically, TRC-6 demonstrated a remarkable strength of 562.9 MPa post-T8-treatment, surpassing those of TRC-3 and TRC-10 by 9.0 % and 5.2 %, respectively. These findings offer valuable insights for future TRC process designs with the aim of eliminating segregation defects and enhancing the sustainable and efficient production of Al-Cu-Li alloys.

Tailoring texture in a near-α titanium alloy: Insights from strain paths and cooling rate influences

By elucidating the progressive relationship from the rolling stress state to the activation of slip systems and then to lattice rotation, this paper clarifies the influence mechanism of strain paths on the evolution of α-phase texture in near-α titanium alloys. The distinct rolling textures obtained further provide a robust foundation for investigating whether the competition between different α-phase textures changes with varying cooling rates during β→α phase transformation. In this study, initial Ti65 alloy sheets underwent rolling using three different strain paths (UDR/CDR/MSCR), resulting in the production of three foils characterized by distinct textures. Compressive stress during rolling promotes the activation of basal and pyramidal-II slipping, leading to the formation of a TD-split basal texture in α-phase. Tensile stress during rolling promotes the activation of prismatic slipping, ultimately resulting in a [10 1‾ 0]//RD (in the case of UDR) or [21‾1‾ 0]//RD (in the case of CDR) texture. Variations in stress states along different strain paths led to differences in the global Schmid factor distribution of α-phase for slip systems, ultimately resulting in diverse texture evolution. Subsequently, foil samples underwent two-phase region heat treatments, followed by furnace cooling and air cooling. After furnace cooling, the strength of the transverse texture increased in each type of foils. Conversely, after air cooling, no specific α-phase texture consistently exhibited an increasing trend in the three foils.

Research on the analytical model of rolling force for TiAl alloy pack rolling

Pack rolling is a hot rolling process for metals with poor plastic forming. The rolling force model is an important model for pack rolling process. Based on the E. Orowan differential equation and the characteristics of pack rolling process, the analytical model of rolling force for pack rolling process was established. Based on the established rolling force model, the influence of roll diameter, reduction rate, metal layer thickness ratio and shear yield stress ratio on the distribution of rolling stress, neutral angle and connection angle was studied. The results indicate that as the increase of reduction rate and shear yield stress ratio, and the reduction of metal layer thickness ratio, the middle layer metal is more prone to plastic deformation. The basic assumptions of the analytical model were verified through a three-dimensional finite element model. The outer layer metal and the middle layer metal were selected as 304 stainless steel and Ti-Al-2Cr-2Nb alloy for pack rolling experiments, respectively. The error between the calculated results of the analytical model and the experimental results is within 15%. The analytical model of rolling force can accurately predict the rolling force and provide theoretical guidance for the formulation of the pack rolling process.

Effect of post rolling stress on phase transformation behavior of microalloyed dual phase steel

Effect of post rolling stress on phase transformation behavior of microalloyed dual phase steel

Experimental Study on the Thermal Stability of Aluminum Alloy 7075-T651 Structural Parts after Rolling Correction

The rolling correction process can eliminate machining distortions of aluminum alloy 7075-T651 structural parts. The thermal stability of the corrected structural parts under the action of temperature loading, especially the macroscopic shape stability, is key to ensure the safe service of mechanical equipment. In this study, different thermal loads were used to postprocess aluminum alloy 7075-T651 structural parts after rolling correction. The thermal stability of the rolled samples was analyzed by characterizing the microstructure and physical and mechanical properties. The results show no obvious change compared to rolling in the distortion of the parts after temperature treatments at 120 °C, 160 °C, 230 °C and 300 °C; the distortion changes were only 10.48%, 2.74%, 8.13% and 8.70%, respectively. The residual stresses in the rolling areas of the samples decreased by 35.58%, 26.08%, 75.97% and 83.13%, respectively. The microhardness also showed a decreasing trend. There was no obvious change after treatment at 120 °C, but the hardness decreased by approximately 5%, 23% and 56%, respectively, after treatments at other temperatures. However, the rolling stress relaxed under thermal stress. The microstructure change analysis shows that the material microstructure is mainly dominated by static reversion at lower thermal loads. With increasing thermal load, the samples are mainly affected by the static recrystallization effect, the microstructure is gradually blurred, and the hardness decreases significantly. In conclusion, although the residual stresses introduced by rolling would occur in different degrees of stress relaxation under the thermal load, the microstructure changes caused by thermal load did not significantly affect the macroscopic distortion of the samples, and the macroscopic shape of the structural parts after rolling correction had good thermal stability.

Finite Element Analysis of Large Plastic Deformation Process of Pure Molybdenum Plate during Hot Rolling

The rare molybdenum resources are being increasingly used in heavy industries. In this study, the common unidirectional and cross hot rolling operations, for pure molybdenum plates, were numerically simulated by using MSC. Marc software. An elastic–plastic finite element model was employed, together with the updated Lagrange method, to predict stress and strain fields in the workpiece. The results showed that there was a typical three-dimensional additional compressive stress (σy> σz > σx) in the deformation zone, while strain could be divided into uniaxial compressive strain and biaxial tensile strain (εy > εx > εz). Tensile stress σx increased with the accumulation of reduction and the decrease in friction coefficient at the edge of the width spread. More importantly, the interlaced deformation caused by cross-commutations, which were helpful in repairing the severe anisotropy created by unidirectional hot rolling. The evolution of the temperature field of pure molybdenum plate was investigated. The surface quenching depth of the pure molybdenum plate was about 1/6 H under different initial temperatures and reductions. In addition, the fundamental reason for the nonuniform distribution of stress and strain fields was the joint influence of rolling stress, contact friction, and external resistance. By comparing the theoretical simulation value of the model with the experimental verification data, we found that the model was aligning well with the actual engineering.

Effect on Internal Stress of Wound Roll of Heterogeneity of Web Film Thickness in Machine Direction

Effect on Internal Stress of Wound Roll of Heterogeneity of Web Film Thickness in Machine Direction

Effects of Humidity Dependence of Paper Core Internal Stress of Wound Roll

Effects of Humidity Dependence of Paper Core Internal Stress of Wound Roll

Evaluation of elastic-plastic deformation in HSS work roll under coupling of residual stress thermal stress and contact stress during hot rolling

Fatigue damage such as crack and spalling on the work roll surface in hot rolling is caused by comprehensive action of residual stress, thermal stress and contact stress. In this work, a HSS work roll was studied based on the actual hot rolling condition, and high temperature performances of the work roll materials are considered. Finite element method was used to obtain the residual stress distribution of the work roll after quenching and tempering. Then, the coupling mechanism of residual stress, thermal stress and contact stress of the work roll in the bite region are analyzed by a transient thermomechanical model. The results showed that, the maximum equivalent strain and equivalent plastic strain appear at the exit of the bite region. And residual stress and thermal stress account for about 90% of the coupling stress. The accumulation of plastic deformation only occurs in the initial rolling, and the initial temperature influences the plastic deformation accumulation. Furthermore, abnormal rolling often leads to large plastic deformation on the roll surface.

A numerical strategy for predicting the interface stresses in metal strip rolling with small reduction

This paper has developed a numerical strategy for predicting the interface stresses in metal strip rolling at a small reduction. Key rolling factors such as the roll elasticity, fluid lubrication, random asperity contacts, asperity-lubricant interaction, rolling speed and reduction were comprehensively integrated into the numerical analysis. The random asperity contact at the roll-strip interface was addressed by a statistical approach with considering the elastoplastic deformations of surface asperities. A transient average Reynolds equation was utilised to deal with the fluid flow subjected to the interruptions caused by the asperity contacts. With the aid of a dynamic explicit finite element analysis, a novel modularised strategy was established to systematically accommodate the mathematical models governing the above key rolling factors, which allows the affordable computation and the effective predictions of contact characteristics in the strip rolling. It was found that both the lubrication and microscale asperity contacts disturb considerably the contact stresses at the rolling interface, and that a proper selection of rolling conditions can reasonably regulate the stresses.

Finite Element Simulation and Experiments of Laminated Cu Cladding Fe Sheet During Cold Rolling Bonding

ABAQUS was used to simulate the laminated Cu cladding Fe sheet during cold rolling, combining theoretical calculations, and the orthogonal test method was adopted. Meanwhiles, the rolling stress was taken as a consideration index to investigate the cold rolling processing rate, rolling speed, friction factor (upper roller), and friction factor (lower roller) 4, the best process parameters of layered metal copper/steel cold-rolled composite are selected. The results show that the cold-rolling processing rate is 52%, the rolling speed is 75 m/min, and the roller friction factor is 0.2 is the best process parameter. At this time, the rolling stress is small, and the bonding quality is the best. Cu cladding Fe sheet of the above-mentioned production process was taken into annealing experiments, SEM and an energy spectrometer were applied to photograph the surface morphology and the element distribution. The interface thickness was calculated by the diffusion distance of Fe and Cu elements, and the interface morphology and mechanical properties were combined for judgment. The results show that the annealing temperature is [Formula: see text]C and the bonding condition is the best under the condition of 4[Formula: see text]h heat preservation.

Lateral cracks damaging the stability of tensile sheet during tandem rolling conveying

In tandem cold-rolling production, sheet fractures are interrelated to both conveyance stress and transverse cracks during conveyance process. The residual tension or sheet contour cannot completely explain the early fracture problem. It is found that small lateral crack reduces fracture threshold of sheets destructively during cold rolling and coiling processes without rolling stress. Several lateral notches were machined on cold-rolled intermediates of silicon steel to simulate edge cracks in rolling processes. Based on tensile test and laser confocal microscope, the damages of lateral notches on tension resistance of sheets were investigated. Then, the shape effect and size effect of lateral notches were analyzed. The notch depth could negatively affect energy absorption capacity of sheets before tensile fracture. Meanwhile, the sharp notch could deteriorate elongation ability of sheets before necking. Both factors reduced fracture threshold of sheets and tensile redundancy and conveyance stably capacity of tandem rolling mills, promoting sheet fracture.

ENGINEERING PEDAGOGY COURSE MAPPING

Graduate students of technical universities have practical difficulties with learning and successful instructional implementation of the fundamentals of engineering didactics. The paper is focused on the formulation of a thought-provoking curriculum with computational assignments for the course of “Technical University Pedagogic and Methodological Foundations of Engineering Education” (TUPMFEE) for graduate and Ph.D. students. The paper uses computational modelling of behavioral processes in socio-educational systems. The TUPMFEE-curriculum teaches future engineers to apply computational techniques to modeling of socio-technical phenomena. The author-formulated and a computer modeling-supported metaphor for the psycho-educational effects of high social pressure impact on student learning dynamics was allegorically visualized using mechanical rolling stress distribution for the nonlinear social process of student knowledge acquisition during instructor-enhanced education with description of some successive forgetting of the previously acquired instructional material upon the studied course completion. The author-proposed TUPMFEE-course successfully triggers graduate students’ interest in both social, mechanical and computer sciences.

Fatigue failure risk evaluation of bimetallic rolls in four‐high hot rolling mills

AbstractIn hot rolling mills, bimetallic rolls are used because of the excellent hardness and wear resistance by applying high‐speed steel (HSS) and ductile casting iron (DCI). Because most of the previous studies focused on surface spalling, almost no study is available for internal fatigue failure based on the stress during the rolling. In this study, therefore, a three‐dimensional finite element method is applied to investigate the rolling stress of the work roll in the four‐high rolling mill. A suitable chamfer geometry in the backup roll is discussed as well as the standard wear profile by considering those effects on the fatigue. Then, to evaluate the fatigue risk under compressive mean stress, the fatigue limit lines in the stress amplitude versus mean stress diagram are newly discussed. With the aid of previous experience in industries, the fatigue fracture risk is discussed by focusing on three critical points inside the work roll.

Fabrication of transparent quartz roll mold using a roll-to-plate wrapping process for flexible electronics

In this study, we numerically simulated the equivalent stress and deformation of a brittle quartz roll with the aim of optimizing its structure and conditions of use in roll-to-plate (R2P) wrapping with a transparent quartz roll. Initially, we analyzed the equivalent stress and contact phenomena between the quartz rolls and the flexible mold by varying the structural parameters of two differently structured quartz rolls to optimize the structure of the R2P system. The results of our analysis enabled us to determine the structure of the R2P system with a polydimethylsiloxane (PDMS) wrapped quartz roll. Further, we analyzed the effects of the thickness of the PDMS cushion and the E-modulus on the stress experienced by the quartz roll and optimized these parameters for the R2P wrapping process. Finally, we applied the optimized quartz roll structure and condition to the actual R2P wrapping process. In addition, we used our wrapped transparent quartz roll mold for the R2R imprint lithography of a micropattern.

Fatigue Failure Analysis for Bimetallic Work Roll in Hot Strip Mills

In hot rolling of steels, bimetallic rolls consisting of high‐speed steel and ductile casting iron are extensively used because of their excellent hardness and wear resistance although the fatigue failure study is not available. To extend the roll life service, herein, a 3D finite element method is applied to investigate the residual stress and the rolling stress of the bimetallic work roll in the four‐high rolling mill. The residual stress is analyzed by considering preheating, quenching, and tempering. Using the results as an initial condition, the rolling stress analysis is carried out consecutively. Then, the fatigue failure risk is discussed focusing on several critical points subjected to the largest stress amplitude inside of the work roll. The accuracy of the simple superposition method is also discussed to evaluate the risk conveniently.

Modelling and Simulation of Mechanical Loads and Residual Stresses in Deep Rolling at Elevated Temperature

Based on the concept of Process Signatures, the deep rolling process is analyzed, aiming at functional relationships between material modifications and internal material loads during the process. The focus of this work is to investigate the influence of the workpiece temperature on the generated residual stress components. For this purpose, extensive finite element simulations of deep rolling were conducted, taking into account the effect of neighboring tool paths on the internal material loads and residual stress. A kinematic strain hardening model was parameterized and utilized and the simulations were validated experimentally. Simulated residual stresses agree qualitatively well with measurements and show a strong influence of the workpiece temperature as expected. Process Signature Components were generated, taking into account the maximal and minimal residual stress as well as their respective positions beneath the workpiece surface.

Study of residual casting stresses in cast iron rolling rolls

The metal magnetic memory method (MMM) is a fundamentally new direction in technical diagnostics. It is the passive method that uses information emitted by a product or structure. In addition to early detection of a developing defect, the MMM provides information about the actual stress-strain state of the test object. When diagnosing equipment using the metal magnetic memory, the main criterion for stress concentration zones is the presence in this zone of lines characterized by a change in the sign of the normal component of the intrinsic stray field. Studies have shown that storing the rolls during 22 days significantly reduces the residual stress level. An increase in the duration of the roll storing contributes to a greater reduction in stresses in castings. The studies have shown that the MMM method application made it possible to assess the unevenness of the stress-strain state of the rolls and to identify the stress concentration zones - the sources of cracking. Storing the rolls after casting leads to a significant reduction in the level of residual stresses. Rough machining results in the appearance of zones with an increased level of residual stresses, which can initiate the formation of cracks in rolls during their operation. The use of the MMM method will enable to develop a technology for accelerated stress relief in castings of rolls after their machining, eliminating aging.

Determination of the Biaxial Anisotropy Coefficient Using a Single Layer Sheet Metal Compression Test

Numerical process design leads to cost and time savings in sheet metal forming processes. Therefore, a modeling of the material behavior is required to map the flow properties of sheet metal. For the identification of current yield criteria, the yield strength and the hardening behavior as well as the Lankford coefficients are taken into account. By considering the anisotropy as a function of rolling direction and stress state, the prediction quality of anisotropic materials is improved by a more accurate modeling of the yield locus curve. According to the current state of the art, the layer compression test is used to determine the corresponding Lankford coefficient for the biaxial tensile stress state. However, the test setup and the test procedure is quite challenging compared to other tests for the material characterization. Due to this, the test is only of limited suitability if only the Lankford coefficient has to be determined. In this contribution, a simplified test is presented. It is a reduction of the layer compression test to one single sheet layer. So the Lankford coefficient for the biaxial tensile stress state can be analyzed with a significantly lower test effort. The results prove the applicability of the proposed test for an easy and time efficient characterization of the biaxial Lankford coefficient.