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A beam formulation based on reproducing kernel particle method (RKPM) for the dynamic analysis of stiffened shell structures is presented in this paper. The kinematic description of a beam is obtained based on the Timoshenko beam theory. By using the principle of virtual power, the governing equations of a three-dimensional beam are derived. To obtain the numerical model of stiffened shell structures, two schemes are adopted: one is model stiffeners by the RKPM beam formulation, the other one is model the entire stiffened shell by the RKPM shell formulation. In the first scheme, the coupling model of RKPM shell and beam formulation is obtained by adding the corresponding quantities in their governing equations. In the second scheme, by determining the support domain of a stress point according to which component the stress point is located, the full shell simulation is achieved. The reliability and accuracy of those two schemes are verified by several numerical examples. [ABSTRACT FROM AUTHOR]

Abstract  This paper deals with the characterization of creep properties and recoverability of double-wall corrugated paperboard with A and B flutes at different combined conditions of the ambient temperature 20°C with four kinds of relative humidities and five kinds of constant compression loads. The main feature of this paper is the evaluation on the creep properties and recoverability of double-wall corrugated paperboard with A and B flutes by a series of experimental studies on creep testing apparatus, the analysis of effects of relative humidities and constant compression loads on creep properties and recoverability, and the establishment of mathematical model of creep and time curves. By using Method of the Least Square and Method of Nonlinear Regression, the piecewise experimental formulas of creep and time curves have been obtained. The work provides basic data and introduces important mathematical relationships relevant to design applications for protective packaging for transportation and storage of goods. [ABSTRACT FROM AUTHOR]

This paper is devoted to analytical and numerical studies of global buckling of a sandwich circular plate. The mechanical properties of the plate core vary along its thickness, remaining constant in the facings. The middle surface of the plate is its symmetrical plane. The mathematical model of the plate is presented. The field of displacements is formulated using the proposed nonlinear hypothesis that generalizes the classical hypotheses. The equations of equilibrium are formulated based on the principle of stationary total potential energy. The proposed mathematical model of the displacements considers the shear effect. The numerical model of the plate is also formulated with a view to verify the analytical one. Numerical calculations are carried out for the chosen family of plates. The values of the critical load obtained by the analytical and numerical methods are compared. The effects of the material properties of the core and the change of the plate radius on the critical load intensity are presented. [ABSTRACT FROM AUTHOR]

Polymer networks usually have many entanglements as well as a finite extensibility due to the uncrossability and the full stretching of the network chains. In this paper, the nonaffine model proposed by Davidson and Goulbourne is adopted to characterize the influence of entanglements and finite extensibility of the polymer chains on the mechanical behavior of hydrogels. The Davidson-Goulbourne model only contains three material parameters and has a simpler mathematical form than the Edwards-Vilgis slip-link model, which is the only model that has been adopted to characterize the influence of entanglements on the swelling deformation of polymeric gels so far. Some benchmark problems such as free swelling, constrained swelling, uniaxial tension, equibiaxial tension in the immersed state and uniaxial compression in the isolated state are analyzed, respectively, based on the new constitutive equations. The results show that entanglements as well as chain extensibility have important influences on the mechanical response of hydrogels. [ABSTRACT FROM AUTHOR]

Under the load conditions of clamping force and riveting force, the part deformation problems are induced in the assembly process. For the component deformation problems of the thin-wall part assembly, in this paper, from the viewpoint of micro-aspect, the fractal theory model is proposed to analyze the relationship between the part deformation, loads, and contact area for rivet-joint parts; the micro-deformation values for different stages are solved and obtained through theoretical analysis. According to the self-similarity of fractal theory model, the change of the micro-convex body for contact surface will be researched to reflect the macro-deformation properties. Through the measuring experiment for thin-wall parts, the actual three-dimensional coordinate value of each measuring point is obtained before and after riveting assembly, and then, the wavelet neural network method (WNNM) is adopted to predict experiment deformation value based on the obtained deformation value after processing the coordinate value through fitting surface method. Hereby, according to the deformation value for every thin-wall part after processing experiment data, the fractal dimension value will be determined based on the fractal statistic method to analyze the deformation status of different stages. Through analysis and comparison, the results show that the variation regularity of deformation value based on two or three fractal deformation stages is well conformed to and similar to the experimental value and prediction value, which also verify the correctness and effectiveness of the theoretical model, and provide a theoretical basis for further research on thin-wall part assembly deformation from a micro-perspective and improving assembly accuracy quality in future. [ABSTRACT FROM AUTHOR]

During the assembly process of CNC machine tool, the assembly dimensions are varied due to the effect of the component deformation caused by gravity. Hence, a mathematical model predicting assembly errors needs to be constructed considering component deformation before tolerance design process. This paper presents an assembly error model of linear axis of CNC machine tool to analyze the effects of component manufacturing error and deformation on axis based on the 3-2-1 localization theory. Thereafter, axis position and angular deviations are calculated under four different conditions, ideal condition, condition considering manufacturing error only, condition considering the effect of structure, and actual condition. At last, the effect of worktable gravity on Y-axis deformation is taken as an example to verify the model. This model can be used to verify the tolerance at tolerance design or to calculate modification amount in assembly process. [ABSTRACT FROM AUTHOR]

The objective of research in this paper refers to the theoretical and experimental determination of dynamic sizes that occur during the process of impact of railway wagons. At the process of wagons impact as well as at the time of changes of movement regime (starting, stopping, and braking), the longitudinal forces that significantly affect the stress-deformational state of the supporting wagon structure occur. In the process of developing and designing new types of wagons and in the process of identifying the behavior of existing types of wagons, it is necessary to know the values of the most important dynamic sizes that occur during the process of impact. In this paper, a method for determining these sizes is formed by using the theoretical models of impact of wagons. Results of numerical simulation of impact are compared with the results of experimental tests, which were conducted according to international regulations. Research has shown that the results of numerical simulations coincide with the results of experimental tests, with certain exceptions. It is concluded that theoretical model can be used in determining the most important dynamic sizes that occur during the process of wagons impact. [ABSTRACT FROM AUTHOR]

In a free-state condition, deformable bodies (or compliant parts) have a significantly different shape than their nominal geometry (CAD model) due to gravity loads and residual stress. Typically, the dimensional metrology of such parts requires a particular approach where expensive and specialized jigs are needed to constrain and follow the component during inspection. This paper proposes a new method to fixtureless inspect deformable bodies by adapting the coherent point drift (CPD) algorithm. This new approach combines the optimization of the smoothness regularization parameters of the CPD powerful non-rigid registration method alongside the Thompson-Biweight statistical test as an identification method to distinguish profile and localization process manufacturing defects from a part's deformation. In other words, a new 'flexible' registration approach that meets the specifications of compliant parts is proposed. The CAD model is smoothly modified to fit the scanned part by minimizing two criteria that belong to deformable bodies. The first criterion is the conservation of the curvilinear distance (isometric transformation). That is to say, the condition that the stretch difference between the original CAD model and the modified one should be very small. The second criterion is the usual minimization of the Euclidean distance between the modified CAD model and its corresponding scanned part. Many case studies were performed on a typical industrial sheet metal which presented profile and localization defects. The estimated values of the defects, as well as their positions, are much closer to their reference ones in most cases, thus reflecting the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Material constitutive model is one of the basic scientific fundamentals for simulation accuracy of high-speed cutting (HSC). A high-speed orthogonal cutting method (HS-OCM) based on the shear slip distance, aided by split Hopkinson pressure bar (SHPB) experiments, is proposed in this paper to obtain the shear slip deformation characteristics in the HSC of 6061-T6 aluminum alloy. The Johnson-Cook (JC) model was modified in three ways according to the variation tendencies of the effect curves of strain hardening, strain rate strengthening, and thermal softening, and an improved material constitutive model was obtained. The simulation validations of the obtained material constitutive models were executed. It was found that the modified JC model improves simulation accuracy, i.e., the maximum simulation errors of the cutting force and cutting temperature are 18.5 and 12.2 %, respectively. The HS-OCM avoids the cutting speed limitation (<700 m/min) of the quick-stop test usually used in conventional OCM and the difficulty of predicting tendency inflection points of the inverse identification method employing a finite element simulation model, and allows the experimental measurement of the deformation characteristics of 6061-T6 aluminum alloy in high-speed (2000 m/min) cutting. During HSC of 6061-T6 aluminum alloy, the shear stress, shear strain rate, and deformation temperature in the primary deformation zone increase with increasing cutting speed, whereas the shear strain decreases. [ABSTRACT FROM AUTHOR]

Electrochemical machining (ECM) provides an economical and effective way for machining heat-resistant, high-strength materials into complex shapes that are difficult to machine using conventional methods. It has been applied in several industries, especially aerospace, to manufacture blisk. The electrolyte flow field is a critical factor in ECM process stability and precision. To improve the process stability and the efficiency of blisk cascade passages, ECM with a radial feeding electrode, a rational electrolyte flow mode for electrochemical machining called 'Π shape flow mode', is discussed in the paper. Three flow field models are described separately in this report: traditional lateral flow mode, positive flow mode and Π-shaped flow mode, and the electrolyte velocity and pressure distribution vectors for each flow mode are calculated by means of a finite element fluid analysis method. The simulation results show that the electrolyte flow is more uniform with the Π-shaped flow mode. The deformation of the cathode, which is caused by the pressure difference, is also analysed in this report. The cascade passage ECM with a radial feeding electrode was experimentally tested out to evaluate the rationality of the flow field, and the fluctuation of current during the process was less than 1 %, which means that the process that uses the Π-shaped flow mode is stable. The feeding velocity of the cathode with the Π-shaped flow mode is approximately 70 % higher than that with the other two flow modes, and the incidences of short circuiting are obviously decreased. The surface roughness of the blisk hub is only 0.15 μm, and the machining error of the hub is less than 0.1 mm. The results demonstrate that using the Π-shaped flow mode can enhance the quality, stability and efficiency of blisk cascade passage ECM. [ABSTRACT FROM AUTHOR]

Shape memory alloys (SMAs) provide an attractive solid-state actuation alternative to engineers in various fields due to their ability to exhibit recoverable deformations while under substantial loads. This feature is of particular importance when utilising the smart composite materials reinforced by SMA. Many constitutive models describing this repeatable phenomenon have been proposed, where some models also capture the effects of rate-independent irrecoverable deformations in SMAs. This paper presents experimental investigations and numerical simulations on shape memory alloys. First, by consisting in determining the transformations of equiatomic Ti-Ni shape memory alloys by differential scanning calorimeter. Then, in order to validate a 3D numerical model of the pseudoelastic behaviour of SMA allowing a finite strain analysis, a set of experimental tests at various initial temperatures is proposed. Finally, the numerical simulations of uniaxial tests performed on shape memory alloys are presented and compared with experimental data, permitting the validation of the proposed modelling. Reasonably good correlation is obtained between the experimental and model predictions. [ABSTRACT FROM AUTHOR]

Burr is an important character of the surface quality for machined parts, and it is even more severe in micro cutting. Due to the uncut chip thickness and the cutting edge radius at the same range in micro cutting process, the tool extrudes the workpiece with negative rake angle. The workpiece flows along the direction of minimum resistance, and Poisson burr is formed. Based on the deformation analysis and experiment observations of micro cutting process, the factor for Poisson burr formation is analyzed. It is demonstrated that the ratio of the uncut chip thickness to the cutting edge radius plays an important role on the height of Poisson burr. Increasing the uncut chip thickness or decreasing the cutting edge radius makes the height of exit burr reduce. A new model of micro exit burr is established in this paper. Due to the size effect of specific cutting energy, the exit burr height increases. The minimum exit burr height will be obtained when the ratio of uncut the chip thickness to the cutting edge radius reaches 1. It is found that the curled radius of the exit burr plays an important role on the burr height. [ABSTRACT FROM AUTHOR]

The development of precision machine tools requires an accurate understanding of the thermal behaviour of the tools. Therefore, by developing highly accurate machine tool thermal behaviour simulations, it can accurately forecast the functional performance of a machine tool at the prototype design stage and provide guidance on its design and performance optimization. To improve the accuracy of the thermal simulation of machine tools, it proposed whole-machine temperature field and thermal deformation modeling and a simulation method for vertical machining centers. Based on the studies of thermal-structure coupling finite-element data flow and its critical conditions, it also proposed design and computational methods for obtaining the heat-source power, when various rotational speeds, the forced convection heat transfer coefficient between a rotating surface and the air, the combined heat transfer coefficient between a stationary surface and the air/environment, and key contact surface thermal resistances were considered. Furthermore, this paper performed finite-element simulation analysis based on the constructed whole-machine thermal model, and the temperature characteristics and heat deformation mechanism/state were obtained. After comparing the simulation and experimental results, it verified the effectiveness of the finite-element simulation model and the relevant methods and confirmed that the simulation accuracy for both the temperature characteristics and the thermal deformation had been improved significantly, with a simulation error less than 10 %. [ABSTRACT FROM AUTHOR]

An accurate approach of the instantaneous undeformed chip thickness is a key issue for analyzing milling process. The presented models for approximating instantaneous undeformed chip thickness are oversimplified and complex for use in academic and manufacture practice. In this paper, a new model for determining the undeformed chip thickness in milling process with higher accuracy is proposed. According to the true trochoid path of tool tooth, the true instantaneous undeformed chip thickness can be derived by solving the deduced transcendental equation. An iterational algorithm is used to approach the value in the transcendental equation with infinitesimal calculation error. Our main contributions include that the accurate positions of the geometric points of the undeformed chip profile with different level of width of cut are analyzed and derived, as well as the accurate undeformed chip thicknesses of the chip cross-section profile are approached by iterative algorithm. Case studies with different parameter combinations show that the new model has a higher accuracy compared with the presented models. With this innovative approach, a method of accurate prediction of the geometric profile and thickness of the undeformed chip profile in milling process is provided. [ABSTRACT FROM AUTHOR]

As a widely used engineering material, optical glass is very difficult to process because of its high hardness and brittleness. The material removal mechanism still needs further investigation. In this paper, a mesh-free simulation method—smooth particle hydrodynamics (SPH)—is introduced and an ultra-precision cutting model for K9 glass is provided. Compared with conventional finite element method, the SPH method can effectively avoid mesh distortion when dealing with large deformation problems such as cutting. Several numerical simulations were carried out to further investigate the critical value of transition. Simulation results indicate that when cutting depth is small enough, the K9 glass can be machined in ductile mode and a relatively smooth machined surface without crack can be obtained. The chip is always in irregular and discontinuous way no matter what the cutting mode is. Three cutting tools with different rake angle were used in simulation and the effect of rake angle is analyzed. [ABSTRACT FROM AUTHOR]

Cutting force coefficients are the key factors for efficient and accurate prediction of instantaneous milling force. To calibrate the coefficients, this paper presents an instantaneous milling force model including runout and cutter deformation. Also, forming of surface error is analyzed, and a surface error model considering runout is proposed. Using surface errors of two experiments completed with the same cutting conditions but different axial depth only, cutter deformation is obtained. Then, a new approach for the determination of instantaneous cutting force coefficients is provided. The method can eliminate influences of the other factors except cutter deformation and runout. A series of experiments are designed, and the results are used to identify the parameters. With the evaluated coefficients and runout parameters, the instantaneous milling force and surface error are predicted. A good agreement between predicted results and experimental results is achieved, which shows that the method is efficient, and effect of runout on surface error is not negligible. [ABSTRACT FROM AUTHOR]

Tubular channel angular pressing (TCAP) process was proposed recently as a novel severe plastic deformation technique for producing ultrafine grain and nanostructured tubular components. In this paper, an upper-bound approach was used to analyze the TCAP process. Deformation of the material during TCAP process is analyzed using upper-bound analysis to determine maximum required load. The effects of TCAP parameters such as channel and curvature angles, deformation ratio ( R/ R) and tube material on the process pressure were investigated. The results showed that an increase in the second channel angle and decrease in the ratio R/ R lead to lower process loads. In the first and third curvature angles ranging from 25 to 65°, the required load remains almost constant. The apparent punch load decrease when hardening exponent n is increased. To verify the theoretical results, the finite element (FE) modeling was employed. Good agreement was observed between the predicted pressure from upper-bound analysis and FE results. [ABSTRACT FROM AUTHOR]

In this paper, a polygonal-FEM technique is presented in modeling of arbitrary interfaces in large deformations. The method is used to model the internal interfaces and arbitrary geometries using a uniform non-conformal mesh. The technique is applied to capture discontinuous deformations in the non-conformal elements, which are cut by the interface in a uniform regular mesh. In this approach, a uniform non-conformal mesh is decomposed into sub-elements that conform to the internal interfaces. The geometry of interface is used to produce various triangular, quadrilateral and pentagonal elements at the intersection of interface with regular FE mesh, in which the extra degrees-of-freedom are defined along the interface. The level set method is employed to describe the material geometry on the background mesh. The technique is used to extrude any arbitrary geometry from an initial background mesh and model under different external effects. An important feature of the technique is the decomposition of the uniform non-conformal mesh to the polygonal-FEM mesh, which is conformed to the material interfaces. Finally, several numerical examples are analyzed to demonstrate the efficiency of proposed technique in modeling arbitrary interfaces in large deformations. [ABSTRACT FROM AUTHOR]

This paper proposes a novel modeling methodology for machine tool thermal error. This method combines the advantages of both grey model and artificial neural network (ANN) in terms of data processing. To enhance the robustness and the prediction accuracy, two kinds of grey neural network, namely serial grey neural network (SGNN) and parallel grey neural network (PGNN), are proposed to predict the thermal error. Experiments on the axial directional spindle deformation on a five-axis machining center are conducted to build and validate the proposed models. The results show that both SGNN and PGNN perform better than the traditional grey model and ANN in terms of prediction accuracy and robustness. So the new models are more suitable for complex working conditions in industrial applications. [ABSTRACT FROM AUTHOR]

Based on the theory of mixtures, a coupled thermo-hygro-mechanical (THM) damage model for concrete subjected to high temperatures is presented in this paper. Concrete is considered as a mixture composed of solid skeletons, liquid water, water vapor, dry air, and dissolved air. The macroscopic balance equations of the model consist of the mass conservation equations of each component and the momentum and energy conservation equations of the whole medium mixture. The state equations and the constitutive model used in the model are given. Four final governing equations are given in terms of four primary variables, i.e., the displacement components of soil skeletons, the gas pressure, the capillary pressure, and the temperature. The processes involved in the coupled model include evaporation, dehydration, heat and mass transfer, etc. Through the process of deformation failure and the energy properties, the mechanics damage evolution equations are established based on the principle of conversation of energy and the Lemaitre equivalent strain assumption. Then, the influence of thermal damage on the mechanical property is considered. [ABSTRACT FROM AUTHOR]

Vehicle crashworthiness is an important issue to ensure passengers safety and reduce vehicle costs in the early design stage of vehicle design. The aim of the crashworthiness design is to provide an optimized structure that can absorb the crash energy by controlled vehicle deformations while maintaining enough space of the passenger compartment. Meta-modeling and optimization techniques have been used to reduce the vehicle design cycle. In this paper, a new particle swarm-based optimization method is presented for multi-objective optimization of vehicle crashworthiness. The proposed optimization method is first validated with a multi-objective disk brake problem taken from literature. Finally, it is applied to multi-objective crashworthiness optimization of a full vehicle model and milling optimization problems to demonstrate its effectiveness and validity. [ABSTRACT FROM AUTHOR]

Induced strains play an important role in mining regions and water dam areas. We consider a mechanism of reorganization of the applied stress load by some changes in rock-body defect distribution caused by human activity. A defect content increases with increasing stress load and related deformations; hence, a relationship could appear between seismic risk and deformation level. Recent progress in the Asymmetric Continuum Theory permits to consider some internal reorganization of the applied load due to internal defect content and distribution; in this paper we consider an increase of internal defect densities due to mining works and the appearance of reorganized internal stress distribution. A generalization of the Peach-Koehler forces acting on the defects makes it possible to define formation of induced strains; a character of resulting strains may essentially differ from the applied load. In the case of an axial load, this approach helps to understand formation of shear or rotational micro-fractures, usually recognized as fragmentation and slip motions. [ABSTRACT FROM AUTHOR]

The aim of this paper is to provide a general procedure to extract the constitutive parameters of a plasticity model starting from displacement measurements and using the Virtual Fields Method. This is a classical inverse problem which has been already investigated in the literature, however several new features are developed here. First of all the procedure applies to a general three-dimensional displacement field which leads to large plastic deformations, no assumptions are made such as plane stress or plane strain although only pressure-independent plasticity is considered. Moreover the equilibrium equation is written in terms of the deviatoric stress tensor that can be directly computed from the strain field without iterations. Thanks to this, the identification routine is much faster compared to other inverse methods such as finite element updating. The proposed method can be a valid tool to study complex phenomena which involve severe plastic deformation and where the state of stress is completely triaxial, e.g. strain localization or necking occurrence. The procedure has been validated using a three dimensional displacement field obtained from a simulated experiment. The main potentialities as well as a first sensitivity study on the influence of measurement errors are illustrated. [ABSTRACT FROM AUTHOR]

In recently proposed thermo-elasto-viscoplastic material model for metals, the damage is described by the second-order tensor, called microdamage tensor to express the experimentally observed anisotropy (Perzyna in Mechanics 27(1):25-42, ; Glema et al. in Int J Damage Mech 18(3):205-231, ; Sumelka in The constitutive model of the anisotropy evolution for metals with microstructural defects. Publishing House of Poznan University of Technology, Poznań, ). This variable influences the entire deformation process being modelled, inducing anisotropic response of the material. In this model, the microdamage evolution is additively decomposed into the nucleation and the growth terms. However, for the sake of simplicity, for extremely fast thermomechanical processes, which are considered as a central point, microdamage nucleation term can be omitted. It induces the necessity of the initial anisotropic microdamage state definition in physically justified bounds (growth is possible only for nucleating or existing microdamages). This paper deals with the consequences of different initial microdamage anisotropy assumption, indicating its significant role in proper description of damage. In particular, we conclude that for detailed experimentally observed damage evolution mapped by the model (e.g. macrodamage initiation time, the velocity of macrodamage evolution, the geometry of macrodamage), its anisotropic description is necessary. [ABSTRACT FROM AUTHOR]

This paper addresses the development of a hybrid-mixed finite element formulation for the quasi-static geometrically exact analysis of three-dimensional framed structures with linear elastic behavior. The formulation is based on a modified principle of stationary total complementary energy, involving, as independent variables, the generalized vectors of stress-resultants and displacements and, in addition, a set of Lagrange multipliers defined on the element boundaries. The finite element discretization scheme adopted within the framework of the proposed formulation leads to numerical solutions that strongly satisfy the equilibrium differential equations in the elements, as well as the equilibrium boundary conditions. This formulation consists, therefore, in a true equilibrium formulation for large displacements and rotations in space. Furthermore, this formulation is objective, as it ensures invariance of the strain measures under superposed rigid body rotations, and is not affected by the so-called shear-locking phenomenon. Also, the proposed formulation produces numerical solutions which are independent of the path of deformation. To validate and assess the accuracy of the proposed formulation, some benchmark problems are analyzed and their solutions compared with those obtained using the standard two-node displacement/ rotation-based formulation. [ABSTRACT FROM AUTHOR]

The torsional buckling characteristic of an elastic cylinder with a hard surface coating layer is addressed in this paper. Deformations of the core and surface layer are obtained analytically through the Navier's equation and thin shell model, respectively. Both infinitely and finitely long cylinders are studied and the effects of the surface layer's stiffness, thickness, residual stresses, as well as the cylinder lengths on the critical torsional angle and buckling morphologies, are discussed. It is found that either the surface rippling or global buckling mode may occur when there exist residual stresses within the surface layer. The critical torsional angle increases when the surface layer becomes stiffer and thinner. In addition, higher-order rippling modes frequently occur for a finite-length cylinder with stiffer and thinner surface layer. [ABSTRACT FROM AUTHOR]

Thermal deformation is one of the most significant causes of machining errors in machine tools. One effective method is to build a compensation system to offset the thermal errors. Therefore, an accurate model is the key part of the compensation system. This study proposed a modified Elman network (EN) to improve the prediction accuracy of the compensation model in machine tools. And the improved EN can be regarded as a feed-forward neural network with feedback from hidden layer and output layer as an additional set of inputs. The structure of this network determines its dynamic characteristic with memory function. On the other hand, thermal deformation of the spindle contributes the largest part of total thermal errors in precision machining. Then a precise finite element model of machine tool spindle was established. And a new method for calculating the heat transfer convection coefficient on the surface of the spindle was proposed in this paper. The improved EN was used to map the nonlinear relationship between temperature field and thermal errors of the spindle. At last, a verification experiment was implemented on a CNC center and some satisfying results were achieved. [ABSTRACT FROM AUTHOR]

Helical equilibrium of a thin elastic rod has practical backgrounds, such as DNA, fiber, sub-ocean cable, and oil-well drill string. Kirchhoff's kinetic analogy is an effective approach to the stability analysis of equilibrium of a thin elastic rod. The main hypotheses of Kirchhoff's theory without the extension of the centerline and the shear deformation of the cross section are not adoptable to real soft materials of biological fibers. In this paper, the dynamic equations of a rod with a circular cross section are established on the basis of the exact Cosserat model by considering the tension and the shear deformations. Euler's angles are applied as the attitude representation of the cross section. The deviation of the normal axis of the cross section from the tangent of the centerline is considered as the result of the shear deformation. Lyapunov's stability of the helical equilibrium is discussed in static category. Euler's critical values of axial force and torque are obtained. Lyapunov's and Euler's stability conditions in the space domain are the necessary conditions of Lyapunov's stability of the helical rod in the time domain. [ABSTRACT FROM AUTHOR]

This paper deals with mathematical modeling of one of the effective technologies of plastic metal forming — multistep cold metal forging. Experimental results are given on the plastic behavior of metals under cyclic loading at large strains accumulated for one cycle. Based on the experimental data obtained, a plasticity model is developed and shown to be effective in testing and improving the technology of forging a nut blank by using a computer-aided engineering analysis system. [ABSTRACT FROM AUTHOR]

Abstract  In this paper a general solution for the analysis of shear deformable stiffened plates subjected to arbitrary loading is presented. According to the proposed model, the arbitrarily placed parallel stiffening beams of arbitrary doubly symmetric cross section are isolated from the plate by sections in the lower outer surface of the plate, taking into account the arising tractions in all directions at the fictitious interfaces. These tractions are integrated with respect to each half of the interface width resulting two interface lines, along which the loading of the beams as well as the additional loading of the plate is defined. Their unknown distribution is established by applying continuity conditions in all directions at the interfaces. The utilization of two interface lines for each beam enables the nonuniform distribution of the interface transverse shear forces and the nonuniform torsional response of the beams to be taken into account. The analysis of both the plate and the beams is accomplished on their deformed shape taking into account second-order effects. The analysis of the plate is based on Reissner’s theory, which may be considered as the standard thick plate theory with which all others are compared, while the analysis of the beams is performed employing the linearized second order theory taking into account shear deformation effect. Six boundary value problems are formulated and solved using the analog equation method (AEM), a BEM based method. The solution of the aforementioned plate and beam problems, which are nonlinearly coupled, is achieved using iterative numerical methods. The adopted model permits the evaluation of the shear forces at the interfaces in both directions, the knowledge of which is very important in the design of prefabricated ribbed plates. The effectiveness, the range of applications of the proposed method and the influence of shear deformation effect are illustrated by working out numerical examples with great practical interest. [ABSTRACT FROM AUTHOR]

Some basic aspects of electromagnetic radiation (EMR) emission during quasi-static plastic deformation and crack propagation in ASTM B 265 grade 2 titanium sheets are reported in this paper. It has been observed that titanium emits several intermittent EMR signals starting near the yield and continuing up to fracture. The EMR emissions are sensitive to the applied strain rates. The number of EMR emissions shows a parabolic variation with strain rate, exhibiting a maxima. It appears that the temporary pinnings of the dislocations injected from the crack tip, which is essential for the emission of EMR as described in a recent model by the authors, do not adequately occur at high as well as low strain rates. At elevated temperatures, the square of the EMR amplitude is observed to be proportional to $$ \exp {\left( { - {mU} \mathord{\left/ {\vphantom {{mU} {kT}}} \right. \kern-\nulldelimiterspace} {kT}} \right)}, $$ where U is the activation energy for the movement of jogs, k the Boltzmann constant, T the temperature and m ≤ 1.0. [ABSTRACT FROM AUTHOR]

In rapid prototyping (RP) technology, prototypes are constructed by the sequential deposition of material layers. When the deposition process involves temperature gradients, thermal stresses will develop. In this paper, the prototype deformation in fused deposition modeling (FDM) processes is studied, and the essence of the deformation and the interacting principles are analyzed. According to basic hypotheses and simplifications, the mathematical model of the prototype warp deformation is constructed, and each of the influencing factors concretely, including the deposition layers number n, the stacking section length L, the chamber temperature T e, and the material linear shrinkage rate α, is quantificationally analyzed. Based on the analysis results, some issues and phenomena in the FDM process are rationally explained. Furthermore, the improving methods for the reduction of the prototype warp deformation are proposed, and the applying effect is better. [ABSTRACT FROM AUTHOR]

This paper develops an analytical model for the material removal rate during specimen polishing. The model is based on the micro-contact elastic mechanics, micro-contact elastic-plastic mechanics and abrasive wear theory. The micro-contact elastic mechanics between the pad-specimen surfaces used the Greenwood and Williamson elastic model. The micro-contact elastic-plastic mechanics between specimen and particle, as well as the micro-contact elastic mechanics between particle and pad, are also analyzed. The cross-sectional area of the worn groove in the specimen is considered as trapezoidal area. A close-form solution of material removal rate from the specimen surface is the function of average diameter of slurry particles, pressure, the specimen/pad sliding velocity, Equivalent Young’s modulus, RMS roughness of the pad, and volume concentration of the slurry particle. [ABSTRACT FROM AUTHOR]

In this paper, an application of the reproducing kernel particle method (RKPM) is presented in plasticity behavior of pressure-sensitive material. The RKPM technique is implemented in large deformation analysis of powder compaction process. The RKPM shape function and its derivatives are constructed by imposing the consistency conditions. The essential boundary conditions are enforced by the use of the penalty approach. The support of the RKPM shape function covers the same set of particles during powder compaction, hence no instability is encountered in the large deformation computation. A double-surface plasticity model is developed in numerical simulation of pressure-sensitive material. The plasticity model includes a failure surface and an elliptical cap, which closes the open space between the failure surface and hydrostatic axis. The moving cap expands in the stress space according to a specified hardening rule. The cap model is presented within the framework of large deformation RKPM analysis in order to predict the non-uniform relative density distribution during powder die pressing. Numerical computations are performed to demonstrate the applicability of the algorithm in modeling of powder forming processes and the results are compared to those obtained from finite element simulation to demonstrate the accuracy of the proposed model. [ABSTRACT FROM AUTHOR]

This paper presents a variational formulation of viscoplastic constitutive updates for porous elastoplastic materials. The material model combines von Mises plasticity with volumetric plastic expansion as induced, e.g., by the growth of voids and defects in metals. The finite deformation theory is based on the multiplicative decomposition of the deformation gradient and an internal variable formulation of continuum thermodynamics. By the use of logarithmic and exponential mappings the stress update algorithms are extended from small strains to finite deformations. Thus the time-discretized version of the porous-viscoplastic constitutive updates is described in a fully variational manner. The range of behavior predicted by the model and the performance of the variational update are demonstrated by its application to the forced expansion and fragmentation of U-6%Nb rings. [ABSTRACT FROM AUTHOR]

A general approach to simulate the mechanical behaviour of entangled materials submitted to large deformations is described in this paper. The main part of this approach is the automatic creation of contact elements, with appropriate constitutive laws, to take into account the interactions between fibres. The construction of these elements at each increment, is based on the determination of intermediate geometries in each region where two parts of beams are sufficiently close to be likely to enter into contact. Numerical tests simulating a 90% compression of nine randomly generated samples of entangled materials are given. They allow the identification of power laws to represent the evolutions of the compressive load and of the number of contacts. [ABSTRACT FROM AUTHOR]

Welding deformations play an important role in sealing capabilities and service life of welded pipe-flange joints. A numerical procedure for modeling of tack welds in girth butt-welding of such joints is of vital importance for the prediction of transverse shrinkage and flange face deformation, which is directly related to the joint sealing capability. This paper presents a 3-D finite element simulation of a pipe-flange joint to describe the numerical procedure for modeling of tack welds in circumferential joints. Sequentially coupled nonlinear transient thermo-mechanical analysis is performed to simulate Metal Inert Gas (MIG) welding. Single pass butt weld geometry with single “V” for 100 mm nominal diameter pipe with same sized weld neck type ANSI flange of class no. 300 is used. Temperature dependent material properties are used and deposition of filler metal is obtained by element birth and death feature. The peak temperature of the tack during the butt-welding of the tacked model is concluded a key parameter for numerical prediction of deformations, whereas tack temperature has negligible effect on the residual stresses. [ABSTRACT FROM AUTHOR]

The present paper is devoted to the analysis of mechanical and electrical behaviors observed on particulate polymer granular materials. The constituting particles obtained these physical properties by coating the polymer spherical substrate with a conducting polymer: polypyrrole (PPy) which confers electrical conducting properties to the particle, while preserving its mechanical properties. Particle contacts dominate the behavior of the granular media and, consequently, size, morphology, roughness and plasticity of the particles play a crucial role in this behavior. Scanning electron microscope (SEM) and atomic force microscope (AFM) were used to study the surface state and the contact area between neighbors. An experimental set up, based on the measurement of the displacement of contacting particles subjected to a normal force and of the variation of the electrical resistance of the packing, allowed the study of both the mechanical and electrical behaviors of the particle system. The experimental results took into account the plastic deformation under varying loading and unloading conditions; they were consistent with theories of contact mechanics, thus validating the existing models. [ABSTRACT FROM AUTHOR]