Deformation Stability of GH4033 Superalloy in the Hot Continuous Rolling Process Based on Dynamic Material Model and Finite Element Model

The flow stress behavior of GH4033 superalloy was determined by the hot compression tests at the temperatures of 1223-1473 K and the total strains of 0.6 with the strain rates of 0.001-30.0 s^(-1) by using cylindrical samples.The processing maps based on the dynamic material model(DMM)combined with the corresponding microstructure observations indicate the reasonable processing domain locating at the strain rates of 0.1-1.0 s^(-1) and the deformation temperature of 1273-1423 K.Meanwhile,the numerical simulation based on finite element model(FEM)described the variation of the effective strain,effective strain rate and the temperature for the core node,and unveiled the influence of the hot rolling parameters considering the initial temperature(T_(0))range of 1223-1473 K and the first-stand biting velocity(v_(0))range of 0.15-0.35 m·s^(-1).Furthermore,the deformation stability of GH4033 superalloy in the round rod hot continuous rolling(HCR)process is described and analyzed by coupling the three-dimensional(3-D)processing map,and the spatial trajectory lines were determined by the numerically simulated temperatures,the strains and the strain rates.Finally,the results show that the hot deformation stability of GH4033 can be achieved by the rolling process parameters located at T_(0)=1423 K and v_(0)=0.25 m·s^(-1).Additionally,the practical HCR processes as T_(0)=1423 K and v_(0)=0.15,0.25,0.35 m·s^(-1) were operated to verify the influence of the hot rolling parameters on the hot deformation stability by the microstructure observation of the final products.

Elasto-plastic analysis of masonry with anisotropic plastic material model

This paper establishes an anisotropic plastic material model to analyze the elasto-plastic behavior of masonry in plane stress state.Being an anisotropic material,masonry has different constitutive relation and fracture energies along each orthotropic axes.Considering the unique material properties of masonry,a new yield criterion for masonry is proposed combining the Hill's yield criterion and the Rankine's yield criterion.The new yield criterion not only introduces compression friction coefficient of shear but also considers yield functions for independent stress state along two material axes of tension.To solve the involved nonlinear equations in numerical analysis,several nonlinear methods are implemented,including Newton-Raphson method for nonlinear equations and Implicit Euler backward mapping algorithm to update stresses.To verify the proposed material model of masonry,a series of tests are operated.The simulation results show that the new developed material model implements successfully.Compared with isotropic material model,the proposed model performs better in elasto-plastic analysis of masonry in plane stress state.The proposed anisotropic model is capable of simulating elasto-plastic behavior of masonry and can be used in related applications.

Multi-Material Topology Optimization of Structures Using an Ordered Ersatz Material Model

This paper proposes a new element-based multi-material topology optimization algorithm using a single variable for minimizing compliance subject to a mass constraint.A single variable based on the normalized elemental density is used to overcome the occurrence of meaningless design variables and save computational cost.Different from the traditional material penalization scheme,the algorithm is established on the ordered ersatz material model,which linearly interpolates Young’s modulus for relaxed design variables.To achieve a multi-material design,the multiple floating projection constraints are adopted to gradually push elemental design variables to multiple discrete values.For the convergent element-based solution,the multiple level-set functions are constructed to tentatively extract the smooth interface between two adjacent materials.Some 2D and 3D numerical examples are presented to demonstrate the effectiveness of the proposed algorithm and the possible advantage of the multi-material designs over the traditional solid-void designs.

Beam Element Material Model for Rotary-Straightened Steel W-Shapes

An inelastic material model that was previously developed by the author for standard W-Shapes was adapted for use to model the behavior and strength of rotary-straightened hot rolled W-Shape sections.Using a published residual stress model for these W-Shapes,limit load analyses were conducted using the material model in MASTAN2 and were compared with published finite element results.The material model required an adjustment to the initial yield moment conditions and residual stress ratios.Comparisons with published results indicate that these minor modifications were sufficient to provide very good modeling agreement.The previously developed material model can be used effectively to model the limit load conditions of rotary-straightened hot rolled W-Shape beams and beam-columns in steel frames.The effect of rotary-straightening W-Shapes is more significant for minor axis bending conditions and this becomes more pronounced as the floor load magnitudes increase.

An Inelastic Material Model for Lateral Torsional Buckling and Biaxial Bending of Steel W-Shapes

A new material model for beam elements was developed for use as normalized tangent modulus expressions when performing 3-dimensional second-order inelastic analyses of steel I-section beams.The stiffness matrix of a 14 degree-of-freedom beam element was updated to include the effects of yielding on St.Venant’s torsion and bimoment stiffness at the initial and terminal nodes.A validation study compared the new model’s results with those from published detailed finite element analyses and was found to be in very close agreement.A biaxial end-moment study with two different depth-to-flange-width ratios provided expected and consistent results over a range of moment conditions.

Material Model Research on Rubber Vibration Isolators

A viscohyperelastic constitutive model is proposed to describe the mechanical behaviour of vibration isolation rubber under broad-band vibration. This constitutive model comprises two parts： a component with three parameters to characterize the hyperelastic static properties of rubber materials, and the other component incorporating two relaxation time parameters, corresponding to high and low strain rates, respectively, to describe the dynamic response under vibration and impact loadings. Based on this proposed constitutive model, a series of experiments were performed on two types of rubber materials over a wide strain rate range. The results predicted from this model are in good agreement with the experimental data.

Elastic Mechanical Stress Analysis in a 2D-FGM Thick Finite Length Hollow Cylinder with Newly Developed Material Model

In this paper a new 2D-FGM material model based on Mori-Tanaka scheme and third-order transition function has been developed for a thick hollow cylinder of finite length.Elastic mechanical stress analysis is performed by utilizing the finite element method.The corresponding material,displacement and stress distributions are evaluated for different values of nr and nz.Moreover,the effects of different material property distributions on the effective stress with respect to the metallic phase volume fraction are investigated.It is demonstrated that the increase in nr and V_m leads to a significant reduction in the effective stress.Finally,it is shown that the ceramic phase rich cylinder wall has lower maximum effective stresses of which the lowest value of effective stress has been evaluated for nr=20 and nz=5.This minimum value is about half the maximum effective stress which has been evaluated for the non-FGM cylinder case（nr=nz=0.1）.

Correlation between Single Factor Material Constitutive Model Parameters and Temperature for Ti6Al4V Alloy

Accurate material constitutive model is considered highly necessary to perform finite element simulation and analysis.However,it is difficult to establish the material constitutive model because of uncertainty of mathematical relationship and constraint of existing experimental condition.At present,there exists considerable gap between finite element simulation result and actual cutting process.Particular emphases were put on investigating the correlation between ＂single factor＂ material constitutive model parameters and temperature for Ti6Al4V alloy,and also establishment of material constitutive model for this kind of material.Theoretical analyses based on dislocation theory and material functional relations showed that material model was deeply affected by variation temperature.By the least squares best fit to the available quasi-static and high-speed impact compression experiment data,material parameters at various temperatures were found.Experimental curves analyses and material parameters comparison showed that the ＂single factor＂ material constitutive model parameters were temperature dependent.Using the mathematical mapping between material parameters and temperature,＂single factor＂ material constitutive model of Ti6Al4V alloy was established,which was proven to be right by comparing with experimental measurements.This work makes clear that the ＂single factor＂ material constitutive model parameters of Ti6Al4V alloy are temperature dependent.At the same time,an accurate material constitutive model is established,which helps to optimize cutting process and control machining distortion for Ti6Al4V alloy aerospace parts.

Material Removal Model Considering Influence of Curvature Radius in Bonnet Polishing Convex Surface

The bonnet tool polishing is a novel, advanced and ultra-precise polishing process, by which the freeform surface can be polished. However, during the past few years, not only the key technology of calculating the dwell time and controlling the surface form in the bonnet polishing has been little reported so far, but also little attention has been paid to research the material removal function of the convex surface based on the geometry model considering the influence of the curvature radius. Firstly in this paper, for realizing the control of the freeform surface automatically by the bonnet polishing, on the basis of the simplified geometric model of convex surface, the calculation expression of the polishing contact spot on the convex surface considering the influence of the curvature radius is deduced, and the calculation model of the pressure distribution considering the influence of the curvature radius on the convex surface is derived by the coordinate transformation. Then the velocity distribution model is built in the bonnet polishing the convex surface. On the basis of the above research and the semi-experimental modified Preston equation obtained from the combination method of experimental and theoretical derivation, the material removal model of the convex surface considering the influence of the curvature radius in the bonnet polishing is established. Finally, the validity of the model through the simulation method has been validated. This research presents an effective prediction model and the calculation method of material removal for convex surface in bonnet polishing and prepares for the bonnet polishing the free surface numerically and automatically.

Development of Mathematical Model on Preparation of Functionally Graded Material by Co-sedimentation

From the process of sedimentation the mathematical relationships among deposition volume and powder properties as well as sedimentation parameters were deduced. Based on the formula a mathematical model was set up and simulated through the computer. At last the validity of mathematical model was supported by the representative experiment on Ti-Mo system FGM prepared by co-sedimentation.

Hybrid graded element model for transient heat conduction in functionally graded materials

This paper presents a hybrid graded element model for the transient heat conduction problem in functionally graded materials （FGMs）. First, a Laplace transform approach is used to handle the time variable. Then, a fundamental solution in Laplace space for FGMs is constructed. Next, a hybrid graded element is formulated based on the obtained fundamental solution and a frame field. As a result, the graded properties of FGMs are naturally reflected by using the fundamental solution to interpolate the intra-element field. Further, Stefest＇s algorithm is employed to convert the results in Laplace space back into the time-space domain. Finally, the performance of the proposed method is assessed by several benchmark examples. The results demonstrate well the efficiency and accuracy of the proposed method.

Establishment and Analysis on Material Flow Model in Argo-animal Husbandry Ecosystem

This paper analyzed the material flow situation in argo-animal husbandry ecosystem by compartment model. This model was an important mean for investigating the whole structural characteristics in ecosystem. Based on this analysis, characteristics of material cycle and integrity in the system were mastered. As an example of natural conditions in Yonghe Village, Shuangcheng Township, Shuangeheng Municipal, Heilongjang Province, the system of linear differential equations in system was established by extracting each compartment and investigating material flow and stability of this model was proved by Lyapunov linear theory. The result showed that this system could not be interfered by initial value in the state of present, input and output.

STUDY ON JOINING PROCESS FOR LAMINATED OBJECT MANUFACTURING USING METALAS MODELING MATERIALS

In order to solve some key problems associated with the rapid manufacturingof metallic functional part, a new technique using vacuum solid-state pressure diffusion weldingprocess to join the metallic slice sheets is put forward. The following results can be drawn fromthe experiments: only 1 percent shrinkage happened in the stack direction and it came from theregular system error. The atoms diffuse between joint interfaces clearly and new grains formedmeanwhile. The average shear strength of welding zone is more than 100 MPa and micro hardness ofwelding zone is almost the same as that of matrix. It is shown from above results that the vacuumsolid-state pressure diffusion welding process is an available technique to join metal slice sheetsfor the rapid manufacturing of metallic functional parts.

A Biomimetic Model of Fiber-reinforced Composite Materials

In thjs paper. bamboo fiber has been. on micro scale. investigated as a helical. multi-layered hollow cylinder, the stiffness featu res of bamboo bast fiber were compared with those of a multifilament yarn in traditional fiber-reinforced composite materials, Moreover. a biomimetic model of the reinforce ment of fiber-reinforced composite materials was proposed by imitating the fine structure of bamboo bast fiber. The results show that the comprehensive stiffness properties of the cornplicated fine struc ture of bamboo fiber is superior over those of traditional fiber-reinforced composites.

Assessment of residual oil saturation with time-differentiated variable multiple material balance model

This study aims to improve the evaluation of residual oil saturation in water flooded zones based on the material balance model(MBM)with variable multiple for injected water.We investigated the change patterns of rock-electro parameters during waterflooding through the analysis of displacement tests.Our work differentiated the waterflooding into numerous displacement processes and accordingly propose an improved time-differentiated variable multiple MBM.The calculation results of the improved model are more consistent with the displacement experiment data of cores.Furthermore,the improved method was integrated into the comprehensive interpretation platform of offshore logging to analyze water flooded zones of a well in the A oilfield.As a result,the residual oil saturation calculated is in close agreement with the results of experiments on cores.Our results indicate that the time-differentiation and variable multiplier for injected water can effectively enhance the assessment accuracy of the residual oil saturation of water-flooded zones.

MODELING OF LASER MACHINING ON POLYMETHYL METHACRYLATE TO FABRICATE MICROFLUIDIC CHIP

The use of a CO2 laser system for fabrication of microfluidic chip on polymethyl methacrylate （PMMA） is presented to reduce fabrication cost and time of chip. The grooving process of the laser system and a model for the depth of microchannels are investigated. The relations between the depth of laser-cut channels and the laser beam power, velocity or the number of passes of the beam along the same channel are evaluated. In the experiments, the laser beam power varies from 0 to 50 W, the laser beam scanning velocity varies from 0 to 1 000 mm/s and the passes vary in the range of 1 to 10 times. Based on the principle of conservation of energy, the influence of the laser beam velocity, the laser power and the number of groove passes are examine. Considering the grooving interval energy loss, a modified mathematical model has been obtained and experimental data show good agreement with the theoretical model. This approach provides a simple way of predicting groove depths. The system provides a cost alternative of the other methods and it is especially useful on research work of rnicrofluidic prototyping due to the short cycle time of production.

Numerical Model Research on Rotational Performance of Beam-Column High-Strength Bolt Extension End-Plate Connection Node

The high-strength bolted end plate connection is widely used in the construction industry with its green environmental protection and excellent seismic performance. The joints of the joints are semi-rigid, the force performance is extremely complicated, and the experimental research cost is relatively high, and the cycle is very long. Therefore, the establishment of an efficient numerical model is of great significance for evaluating the force performance of high-strength bolt end plates. In this paper, the influence of different material models on the rotation performance of the joint is studied by numerical simulation, and the bending moment-rotation curve is obtained. The numerical simulation and the experimental results are in good agreement, so as to provide a reference for the design and application of this kind of joint.

Mesoscopic Modeling Approach and Application for Steel Fiber Reinforced Concrete under Dynamic Loading:A Review

Steel fiber reinforced concrete(SFRC)has drawn extensive attention in recent years for its superior mechanical response to dynamic and impact loadings.Based on the existing test results,the highstrength steel fibers embedded in a concrete matrix usually play a strong bridging effect to enhance the bonding force between fiber and the matrix,and directly contribute to the improvement of the post-cracking behavior and residual strength of SFRC.To gain a better understanding of the action behavior of steel fibers in matrix and further capture the failure mechanism of SFRC under dynamic loads,the mesoscopic modeling approach that assumes SFRC to be composed of different mesoscale phases(i.e.,steel fibers,coarse aggregates,mortar matrix,and interfacial transition zone(ITZ))has been widely employed to simulate the dynamic responses of SFRC material and structural members.This paper presents a comprehensive review of the state-of-the-art mesoscopic models and simulations for SFRC under dynamic loading.Generation approaches for the SFRC mesoscale model in the simulation works,including steel fiber,coarse aggregate,and the ITZ between them,are reviewed and compared systematically.The material models for different phases and the interaction relationship between fiber and concrete matrix are summarized comprehensively.Additionally,some example applications for SFRC under dynamic loads(i.e.,compression,tension,and contact blast)simulated using the general mesoscale models are given.Finally,some critical analysis on the current shortcomings of the mesoscale modeling of SFRC is highlighted,which is of great significance for the future investigation and development of SFRC.

Finite Element Simulation of Flexible Roll Forming with Supplemented Material Data and the Experimental Verification

Flexible roll forming is a promising manufacturing method for the production of variable cross section products. Considering the large plastic strain in this forming process which is much larger than that of uniform deformation phase of uniaxial tensile test, the widely adopted method of simulating the forming processes with non-supplemented material data from uniaxial tensile test will certainly lead to large error. To reduce this error, the material data is supplemented based on three constitutive models. Then a finite element model of a six passes flexible roll forming process is established based on the supplemented material data and the original material data from the uniaxial tensile test. The flexible roll forming experiment of a B pillar reinforcing plate is carried out to verify the proposed method. Final cross section shapes of the experimental and the simulated results are compared. It is shown that the simulation calculated with supplemented material data based on Swift model agrees well with the experimental results, while the simulation based on original material data could not predict the actual deformation accurately. The results indicate that this material supplement method is reliable and indispensible, and the simulation model can well reflect the real metal forming process. Detailed analysis of the distribution and history of plastic strain at different positions are performed. A new material data supplement method is proposed to tackle the problem which is ignored in other roll forming simulations, and thus the forming process simulation accuracy can be greatly improved.