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The thermal response in paper has been studied by thermography. It was observed that an inhomogeneous deformation pattern arose in the paper samples during tensile testing. In the plastic regime a pattern of warmer streaks could be observed in the samples. On the same samples digital image correlation (DIC) was used to study local strain fields. It was concluded that the heat patterns observed by thermography coincided with the deformation patterns observed by DIC. Because of its fibrous network structure, paper has an inhomogeneous micro-structure, which is called formation. It could be shown that the formation was the cause of the inhomogeneous deformations in paper. Finite element simulations was used to show how papers with different degrees of heterogeneity would deform. Creped papers, where the strain at break has been increased, were analysed. For these paper it was seen that an overlaid compaction of the paper was created during the creping process. During tensile testing this was recovered as the paper network structure was strained. [ABSTRACT FROM AUTHOR]

Cutting toolholders, with designed in-built compliant mechanisms, are frequently used for machining microfeatures. In this paper, compliant structures are designed using trusses as they exhibit a superior strength-to-weight ratio. Systematically stacked two-stage truss structures along with flexure hinges are designed to yield the desired precise cutting motion. The materially reduced efficient design amplifies the output force and greatly assists in overcoming cutting resistance during machining. The characteristics of the designed compliant tool holder are analysed by considering the output force and displacement for a given input. Both mathematical modelling to determine the force and finite element analysis to identify the critical stress regions when subjected to a prescribed input displacement are presented. As part of dynamic analysis, modal analysis and harmonic response studies were performed to determine how the trussed compliant structure deforms when subjected to dynamic loadings. The designed tool holder was additively manufactured using functionally rigid polyamide-12-glass-bead (PA12-GB) material. The performance of the developed cutting tool holder is then verified by machining radially graded surfaces following which, the machining results are presented in this paper. [ABSTRACT FROM AUTHOR]

This paper addresses the problems of easy deformation, difficult dimensional control and difficult accuracy assurance during the production of thin-walled gears for helicopter spoke cutting. It uses finite element simulation technology, metal cutting principles, process optimization and other design and manufacturing technologies to reveal the causes of cutting deformation, effectively predict the deformation of parts during cutting, and develop reasonable deformation control strategies. This study explores the effects of cutting force, residual stress and clamping method on gear machining deformation. The deformation of the spoke plate is analysed by finite element simulation. Abaqus software is adopted to establish a finite element model for 2D turning simulation to predict the machining residual stresses and cutting forces during gear turning machining with different cutting parameters. The simulated cutting forces are compared with the residual stresses and experimentally measured values to verify the accuracy of the finite element model and provide a theoretical basis for model construction in the next simulation study. With Abaqus software, the effect of different cutting forces on the deformation of the spoke plate is simulated, and the effect of the superposition of cutting and clamping forces on the deformation of the spoke plate is simulated using life and death cell technology to simulate the machining of the workpiece. Then, a corresponding fixture is designed to realise the corresponding clamping position for machining experiments, and the deformation of the spoke plate is measured by CMM (coordinate measuring machine) to verify the realism of the simulation. This research provides scientific theoretical guidance and process support for aerospace thin-walled gear spoke plate turning. [ABSTRACT FROM AUTHOR]

In order to reduce the machining deformation of thin-walled parts during milling, a non-uniform allowance planning method for thin-walled parts based on the workpiece deformation constraint with the idea of adding materials in reverse material removal sequence is proposed in this paper. This method does not require accurate deformation prediction and extensive experiments compared to traditional error compensation methods. It strives to maximize the allowance to enhance the stiffness of the in-process workpiece. First, a cutting force threshold calculation method is proposed according to the finite element method. The cutting force threshold at different positions is calculated by obtaining the local stiffness characteristics at the cutter-contact point under the constraint of allowable deformation. And then, the maximum machining allowance at the cutter-contact point is calculated depending on the cutting force model. Considering that the stiffness of the workpiece is position-dependent and affected by material removal, the stiffness of the workpiece is updated by adding elements in the reverse cutting direction, and the finishing stock is obtained by surface fitting. Experimental results show that compared with the traditional uniform allowance method, the error of the proposed method is reduced by about 83%, which can effectively reduce the deformation and improve the machining accuracy. [ABSTRACT FROM AUTHOR]

Filament-wound flexible pipes are widely used to transport fluid in pipeline systems, proved extremely useful in marine engineering. The hyperbolic flexible pipes have good vibration suppression performance, but they are easily deformed under internal pressure. This paper focuses on the stability of hyperbolic flexible pipes based on the composite Reissner shell theory and the transfer-matrix method. The nonlinear stretch of the reinforced filament and the fiber bridge effect are considered in the model. The calculation results show that a large winding angle reduces the deformation and the meridional stress. The available initial winding angle is limited by the geometry and the slippage coefficient of flexible pipe. The reinforced filament of high tensile modulus will reduce the deformation of the pipe. Compared with the geodesic winding trajectory, non-geodesic winding trajectories improves the stability of the pipe. The theoretical result is verified by the finite element analysis. The investigation method and results present in this paper will guide the design and optimization of more novel flexible pipes in the future. [ABSTRACT FROM AUTHOR]

Aiming at the problems of a large amount of material cutting waste or large forming load when large gear profile forming adopts overall cutting or precision forging process, this paper proposed a three-roller bending process (TRBP) for large gear teeth profile, and analyzed the deformation mechanism of the rack bending, meanwhile the gear chain for roll forming was designed. Finite element analysis (FEA) was carried out to numerically simulate the load effects of both the precision forging process and the TRBP for the large gear teeth profile in 17CrNiMo6. The effects of deformation force and strain of TRBP for large gear teeth profile were analyzed. The results showed that as the deformation temperature and speed increase, the deformation force and strain required by the gear profile gradually change. And the reasonable parameter of TRBP is around 750 ∘ C of deformation temperature and 0.5 mm · s - 1 of speed. Compared with the precision forging process under the same boundary conditions, the deformation force of the gear profile TRBP has decreased by about 99 % which could significantly reduce the tonnage requirement of deforming equipment. [ABSTRACT FROM AUTHOR]

This paper proposes a new sheet forming method that combines electromagnetic forming (EMF) with hydraulic forming called electromagnetic hydroforming (EMHF). Finite element models of both the EMF and EMHF processes were established using ANSYS and ABAQUS. Then, dynamic free bulging deformation of 5052 aluminum alloy during the forming processes was analyzed. The EMF process results in a deformed sheet profile with an uneven conical shape, whereas EMHF leads to a deformed profile with a regular circular shape. This is because during the EMHF process, electromagnetic impact energy is transformed into liquid pressure that is evenly distributed on the sheet surface. When the discharge voltage is 4.5 kV, the maximum deformation speed and strain rate reached 70.6 m/s and 2176.8 s−1, respectively. Thus, EMHF can be considered a high-speed forming method. The simulation results for both EMF and EMHF were verified by experiment at two different discharge voltages. The maximum error was less than 7.4%. [ABSTRACT FROM AUTHOR]

This paper presents a novel approach for removing out-of-plane deformation in stretched metal interconnects by adding a fractal structure to the original meander shape and using an optimized fabrication stack. In thermoformed electronics, in cases where copper is used as conductor, the twisting of meander-shaped structures caused by excessive mechanical stress can cause a non-uniform surface, delamination of the metal interconnect from the substrate, and in some cases, a short circuit to the adjacent tracks. Typically, designers of stretchable electronics use various shapes and widths of the copper interconnect to tackle this issue. Using conventional meander shapes such as horseshoes and U-shapes is not universally practical, especially when stretching is higher than 30 percent leading to significant out-of-plane buckling. Limiting this out-of-plane buckling by reducing the track width is not always applicable, as a minimum width is needed from a technology and conductivity perspective. The presented approach is inspired by computational and experimental studies of multiple meander shapes and fabrication methods. A geometry- and fabrication-based approach is presented, reducing the mechanical stress of almost all possible meander shapes by increasing the meander's path length to accommodate the metal track's produced torque during stretching. An analytical approach is provided for calculating the optimal meander parameters and the optimal fabrication stack is achieved based on simulation results. Experiments and finite element modeling for a case study show the improvement in the stress distribution and reduction of out-of-plane buckling. [ABSTRACT FROM AUTHOR]

Due to the unique low rigidity of thin-walled parts, significant machining deformation may occur in the milling process. A deformation prediction model is presented in this paper while considering the effect of the removed material on the global stiffness matrix. Aiming at reducing the scale of the global stiffness matrix, the super-element method is firstly used and the scale of the stiffness matrix is significantly reduced about 30%. And then, the stiffness matrix of the in-process workpiece (IPW) is directly obtained by eliminating the contribution of the removed nodes in the global stiffness matrix. This method can avoid re-building the geometric model or re-meshing the finite element (FE) model in the machining process. To improve the inverse calculation efficiency of the stiffness matrix, a novel nodes re-sorting method is proposed based on the calculation order of the matrix blocks in LU decomposition and inverse calculation. Furthermore, the optimal stiffness direction is discussed and applying the cutting force in this direction can minimize the machining deformation. The simulation results verified the existence of the optimal stiffness direction. Finally, the simulation and experiment are carried out to validate the accuracy of the proposed model. [ABSTRACT FROM AUTHOR]

Shot peening is widely used in the aeronautical industry to enhance the fatigue life of the parts and form large, thin, and complex components, such as wing and fuselage skins. Previous research on peen forming simulation has rarely considered the influence of the shot peening sequence on the resulting deformed shape. In particular, the study on the mechanics mechanism of asymmetry in double-sided sequential (un-simultaneous) shot peening is not enough. In this study, therefore, experiments based on symmetrical plane strips (Almen-sized Al7075 strip and Almen strip) show that the final deformation is often asymmetrical with the same shot peening parameters in sequence. As the symmetrical surfaces are peened in sequence, the final bending direction is always consistent with the later shot peening effect. To explain this interesting phenomenon, the double-sided symmetrical sequential shot peening process was simulated by finite element method (FEM). The simulation and experiment results verified the universality of asymmetric deformation in double-sided symmetrical sequential shot peening process. A theory analytical model of the stiffness reduction proposed in this paper was used to explain the asymmetric deformation mechanism, and it is verified by three-point bending tests. Some new results obtained by the experiment and simulation are presented. The influences of the strip thicknesses and shot peening pressures on the asymmetric deformation are discussed in double-sided symmetrical sequential shot peening. [ABSTRACT FROM AUTHOR]

Adhesive joints are increasingly employed for bonding critical parts of industrial structures. Therefore, adhesive joints become a key element in design, and their mechanical characterization is of the utmost importance. Significant advancement has been realized for their characterization under quasi-static loadings; however characterization techniques are rather limited for dynamic loadings. Indeed, due to the complex paths of waves through structures, existing dynamic characterization techniques will not characterize only the adhesive joint, but instead will characterize the complete assembly containing the joint and the adherents. Moreover, multiaxiality control of the loading on the adhesive joint is difficult to achieve. This paper proposes an innovative experimental technique for the characterization of adhesive joints under dynamic multiaxial loadings. The experimental method relies on three main components: i) a conventional split Hopkinson pressure bar (SHPB) apparatus, ii) a novel specimen, denoted as DODECA, which enables testing of three distinct multiaxial loadings using the same method and iii) local strain and stress measurements performed by digital image correlation (DIC). The paper describes all steps of the experimental procedure, including the underlying preparation of the specimen and the measuring methods. The stress and strain in the adhesive joint are estimated directly from the experimental data both during loading and at the failure point. Finally, the dynamic material behavior of the adhesive joint is identified from the data. [ABSTRACT FROM AUTHOR]

This paper presents a new joining by forming process capable of attaching a sheet to the end of a tube without the need of accessories and extra materials. The process is named as 'self-pierce riveting of tubes to sheets' and is an extension to sheet-tube connections of the working principle of double-sided self-pierce riveting utilized for connecting two overlapped sheets. The process requires tubes with chamfered ends to be pushed against the sheets and its ends to flare (curl) in order to create an interlocking that holds the sheets and tubes tightly together. The resulting joints are invisible because the interlockings are hidden inside the sheets. The presentation draws from deformation mechanics and identification of the major parameters to characterization of the interlocking and evaluation of the pull-out destructive strength that the new joints are capable to withstand without failure. Aluminium sheets and carbon steel tubes are utilized to demonstrate the effectiveness of the new joining by forming process and to demonstrate its ability to connect sheets and tubes made from dissimilar materials at room temperature. Finite element modelling using an in-house computer program gives support to the presentation. [ABSTRACT FROM AUTHOR]

Thermal error modeling of the spindle plays an important role in predicting thermal deformation and improving machining precision. Even though the modeling method using temperature as the input variable is widely applied, it is less effective due to severe loss of thermal information and pseudo-hysteresis between temperature and thermal deformation. This paper presents a novel modeling method considering heat quantity as the input variable with theoretical analysis and experimental validation. Firstly, the change of thermal state of a metal part being heated is discussed to reveal the essence of the relationship between heat, thermal deformation and temperature, and the theoretical basis of the modeling method proposed in this paper is elaborated. Subsequently, the relationship between thermal deformation and heat quantity is further studied through modeling the thermal deformations of stretching bar and bending beam using heat quantity as the independent variable, and the stretching model is verified based on finite element method. Then, the thermal error models of the spindle are developed with the heat elastic mechanics theory and the lumped heat capacity method. In succession, the parameter identification of thermal error models is carried out experimentally using the least square method. The average fitting accuracy of these models is up to 91.3%, which verifies the good accuracy and robustness of the models. In addition, these models are of good prediction capability. The proposed modeling method deepens the research of thermal errors and will help to promote the application of relevant research results in the actual production. [ABSTRACT FROM AUTHOR]

Finite Element (FE) modeling of machining processes has received growing attention over the last two decades. Since machining processes operate at severe deformation conditions, involving very high strain, strain rate, stress, and temperature, the modeling procedure is still a challenging task even with new advanced software and computers. Therefore, most of the published research works were mainly performed for the simplest configuration of machining known as orthogonal cutting, in which a plane strain deformation state is assumed. This configuration leads to reducing the number of elements in the FE model and the computational time of the solution, compared to conventional machining processes (turning, milling, and drilling). Nevertheless, FE modeling of orthogonal turning is still considered as an open-ended subject as most of the phenomena involved in the orthogonal turning process, which also exist in other machining operations, are not fully well understood. The present review article deals with finite element modeling of orthogonal machining process. The paper consists of several related parts. First, the fundamentals of the FE simulation of orthogonal turning process are briefly described. Then, a detailed review on the FE prediction of machining characteristics including chip morphology, cutting forces, cutting temperature, tool wear, and burr formation is provided. Also, the FE prediction of surface integrity characteristics including residual stresses and microstructural changes is discussed. The influence of input model and parameters including thermal, material, and frictional models as well as size and arrangement of elements on machining and surface integrity characteristics are explained as well. Both technical and statistical aspects of the FE simulation of orthogonal turning are treated. Since there is no review paper thoroughly and specifically discussing the methods and findings of the finite element simulation of turning operations, the present article can be used as a reference for researchers who are active and/or interested in this filed. [ABSTRACT FROM AUTHOR]

Water injection in the aquifer induces deformations in the soil. These mechanical deformations give rise to a change in porosity and permeability, which results in non-linearity of the mathematical problem. Assuming that the deformations are very small, the model provided by Biot's theory of linear poroelasticity is used to determine the local displacement of the skeleton of a porous medium, as well as the fluid flow through the pores. In this continuum scale model, the Kozeny–Carman equation is commonly used to determine the permeability of the porous medium from the porosity. The Kozeny–Carman relation states that flow through the pores is possible at a certain location as long as the porosity is larger than zero at this location in the aquifer. However, from network models it is known that percolation thresholds exist, indicating that the permeability will be equal to zero if the porosity becomes smaller than these thresholds. In this paper, the relationship between permeability and porosity is investigated. A new permeability-porosity relation, based on the percolation theory, is derived and compared with the Kozeny–Carman relation. The strongest feature of the new approach is related to its capability to give a good description of the permeability in case of low porosities. However, with this network-inspired approach small values of the permeability are more likely to occur. Since we show that the solution of Biot's model converges to the solution of a saddle point problem for small time steps and low permeability, we need stabilisation in the finite element approximation. [ABSTRACT FROM AUTHOR]

This paper presents a new joining by forming process named as "double-sided self-pierce riveting" that makes use of tubular rivets with simple geometry placed in-between two sheets to be joined. The sheets are pushed against each other by flat parallel punches so that the rivets are forced through the sheets and their ends are flared (curled) to create mechanical interlocking's which holds the sheets tightly together. The methodology draws from deformation mechanics and identification of major process parameters, to fabrication and destructive testing of joints. Experimental work in AA5754-H111 aluminum sheets and AISI 304 stainless steel tubular rivets was supported by finite element modelling. Results allow concluding that the new process incorporates the advantages of conventional self-pierce riveting and successfully overcomes its main disadvantages, namely the material protrusions above and below the sheet surfaces and the difficulties in joining sheets of dissimilar materials with large thicknesses. The new mechanical joints also have the advantage over those produced by clinching and self-pierce riveting of being invisible, because they are hidden inside the cross section of the overlapped sheets. [ABSTRACT FROM AUTHOR]

In this paper, T-joint of 316L steel is obtained by subsection laser welding method without jig, while a thermal elastic-plastic finite element model considering multi-linear yield stress curves and multi-point constraint equations is developed to estimate welding deformation and residual stress. A simplified heat source model with the actual bead geometry is proposed to reduce the number of finite element meshes. Prediction errors between the simulation and experimental measurement results of angular distortions of three reference lines are −11.0, 0.9, and 7.9 % respectively, and the maximum residual stress is 396 MPa. Meanwhile by microstructure analysis, austenite and ferrite are consisted in weld, segregation and dendritic structures are also observed, while the heat-affected zone is very narrow. In a word, weld line with large travel can be welded by subsection laser welding method without jig, while the finite element method proposed in this paper is effective to predict welding deformation and residual stress. [ABSTRACT FROM AUTHOR]

Ti6Al4V alloy is very hard to flowform at room temperature due to its limited ductility. However, it retains excellent adiabatic heat trapping and thermal softening abilities, which can play an important role in improving the formability. In this paper, a 3-D finite element model of backward flowforming with three staggered rollers has been developed in Abaqus/explicit to study the thermomechanical behavior and the residual stress evolution. The model has been validated via flowforming experiments. The role of the heat generation due to plastic deformation is highlighted by comparing a thermomechanical analysis to a purely mechanical analysis without incorporating the additional heat input due to the plastic work. The maximum predicted temperature rise during cold flowforming is 911 °C, which significantly reduces the flow stress in the deformation zone. The two most important factors, which affect the temperature rise in the deformation zone, are friction coefficient and coolant heat transfer coefficient. Hence, a study has been done to assess the sensitivity of the thermomechanical behavior and the residual stresses towards these factors. The friction between the mating surfaces is helpful, but a friction coefficient higher than 0.1 causes through-thickness strain heterogeneity. An increase in the friction coefficient reduces the residual stresses, while an increase in the convective heat transfer coefficient causes a transition from compressive to tensile residual stress along the thickness of the tube. [ABSTRACT FROM AUTHOR]

Deformation of soft polymeric materials often involves complex nonlinear or transient mechanical behaviors. This is due to the dynamic behaviors of polymer chains at the molecular level within the polymer network. In this paper, we present a computational formulation to describe the transient behavior (e.g., viscoelasticity) of soft polymer networks with dynamic bonds undergoing large to extreme deformation. This formulation is based on an Eulerian description of kinematics and a theoretical framework that directly connects the molecular-level kinetics of dynamic bonds to the macroscopic mechanical behavior of the material. An extended finite element method is used to discretize the field variables and the governing equations in an axisymmetric domain. In addition to validating the framework, this model is used to study how the chain dynamics affect the macroscopic response of material as they undergo a combination of flow and elasticity. The problems of cavitation rheology and polymer indentation under extreme deformation are investigated in this context. [ABSTRACT FROM AUTHOR]

Cold roll-beating forming is an incremental cumulative plastic forming technology that uses rolling wheels to impact and roll a metal target at room temperature. The process parameters of cold roll-beating forming influence the forming process and its accuracy. In this paper, these influences are studied for the case of cold roll-beating forming an external tooth groove. First, the process and characteristics of cold roll-beating forming are analyzed to determine the key process parameters for forming external tooth grooves. Next, forming experiments and finite element simulations are carried out for roll-beating AISI 1045 (DIN C45). The forces, material deformation, and formed surface characteristics are analyzed for the process of cold roll-beating forming of an external tooth groove. Finally, the effects of the roll-beating method, spindle speed, and roll-beating density on the forces, forming defect, angle of the groove profile, and surface roughness are discussed. This study will serve as a reference for reducing forming force, restraining adverse deformation, and controlling forming quality by optimizing process parameters. [ABSTRACT FROM AUTHOR]

In this paper, nine inter-relationships linking the stiffness matrix components of symmetrical or unsymmetrical laminates having transverse matrix cracks in some of the off-axis plies is presented. The crack closure condition under membrane and bending deformations is established and used to obtain the inter-relationships. The derived crack closure conditions and inter-relationships are validated using a numerical model based on previous work by the authors. These inter-relationships include the eighteen stiffness matrix components and are exact within the assumptions made in the classical lamination theory. When using a two-scale finite element-based model, six loading cases would be needed to obtain the complete stiffness matrix. With the obtained inter-relationships, only four loading cases would be needed, thus saving a third of the total amount of information and computing time. [ABSTRACT FROM AUTHOR]

This paper deals with the identification and modelling of the deformation behaviour of DC04 sheet metal. An application of the identified behaviour model in the framework of finite element (FE) simulation of deep drawing is performed. Uniaxial tensile tests in three directions are performed to reveal the in-plane plastic anisotropy of the DC04 sheet. The Hill48 quadratic criterion is introduced to represent the initial plastic anisotropy, while the work hardening is represented by power and exponential type laws. Parameters of the established behaviour model are identified using two methods based on Hill48 criterion. FE simulations of uniaxial tensile tests are carried out to validate the identified parameters and thus retain the identification method giving best fitting of performed tests. The identified plastic behaviour model, including initial plastic anisotropy and hardening, is then introduced in FE simulation of deep drawing of waterproof case for a truck, in which the effect of blank-holder force on the drawpiece quality is analysed in order to determine the optimum thickness. Then, the effect of combination between plastic anisotropy and friction anisotropy on the sheet thickness distribution is investigated. The performed analysis shows that the plastic and friction anisotropies have an effect on the DC04 sheet metal deformation. [ABSTRACT FROM AUTHOR]

The paper presents the isogeometric and the Lagrangian approach to the deformable catenary dynamics undergoing large displacements. The benchmark examples are solved and compared with the finite element approach, solutions from independent sources, and analytical solution where available. The sensitivity to discretization and model parameters is demonstrated in selected cases. The isogeometric approach to the catenary dynamics is proved to be efficient and reliable. [ABSTRACT FROM AUTHOR]

The reduction in the number of coordinates for flexible multibody systems is necessary in order to achieve acceptable simulation times of real-life structures and machines. The conventional model order reduction technique for flexible multibody systems is based on the floating frame of reference formulation (FFRF), using a rigid body frame and superimposed small flexible deformations. The FFRF leads to strongly coupled terms in rigid body and flexible coordinates as well as to a non-constant mass matrix. As an alternative to the FFRF, a formulation based on absolute coordinates has been proposed which uses a co-rotational strain. In this way, a constant mass matrix and a co-rotational stiffness matrix are obtained. In order to perform a reduction in the number of coordinates, by means of the component mode synthesis, e.g., the number of modes needs to be increased, such that all modes are represented in every possible rotated configuration. This approach leads to the method of generalized component mode synthesis (GCMS). The present paper shows in detail how the equations of motion of the FFRF evolve from the ones of the GCMS by considering rigid body constraint conditions and subsequently eliminating them via an appropriate null-space projection. This approach allows a straightforward, term-by-term interpretation of the FFRF mass matrix and of the generalized gyroscopic forces, which, to the same extent, cannot be deduced from former publications on the FFRF. From a practical point of view, the resulting expressions allow to calculate all inertia coefficients from the constant finite element mass matrix together with standard input data of the finite element model in the course of a preprocessing step. Then, the repeated updates of the FFRF mass matrix and of the gyroscopic forces in the course of time integration involve only simple vector matrix operations of low dimensions. In contrast to previous implementations of the FFRF, no evaluations of extra inertia integrals are required. Consequently, the present formulation can be implemented entirely independent of the related finite element code. [ABSTRACT FROM AUTHOR]

In this study, the free vibration analysis of two joined laminated conical shells is investigated. Five equilibrium equations for each conical shell have been derived in a particular coordinate system; using Hamilton’s principle and first-order shear deformation theorem. The analytical solutions are obtained in the form of power series based on separation of variables method. The boundary conditions at both ends of the joined shells and the continuity conditions, at the conical shells contact, are extracted from energy formulations. As a result, the non-dimensional natural frequencies are studied for cross-ply laminated shells. The effects of semi-vertex angle, circumferential modes, number of layers, thickness, length of shells and different boundary conditions on non-dimensional frequencies are considered. As a comparing result, the non-dimensional frequencies and mode shapes are extracted using finite element method (FEM). The results are compared and verified with the previous available results in other researches. The results reveal a good agreement among analytical solutions, FEM and other results. The output of this paper can be used for analyzing cylindrical-conical shells in addition to joined conical shells. [ABSTRACT FROM AUTHOR]

Semi-analytical models have been developed to analyze the contact of inhomogeneous materials based on the equivalent inclusion method. It is important to pursue a higher efficiency in numerical implementation of the semi-analytical models. This paper reports the development of a dual-grid computational scheme for further improving the efficiency of the current semi-analytical modeling. Parametric studies show that the new method can save at least 50% of the execution time with respect to the original algorithm in a considerably wide range of conditions. The new method is applied to investigate the influence of inhomogeneities on contact pressure distributions. Data regression is performed to obtain the amplitudes of contact pressure disturbances as a function of inhomogeneitys elastic modulus, size and location. Then, a criterion is developed based on the values of contact pressure disturbances to determine the circumstances in which the coupling between inhomogeneities and surface contact be ignored. [ABSTRACT FROM AUTHOR]

Soil-filled gabion structures are widely used to protect against the effects of blast and fragmentation. It is known that moisture content significantly affects the capability of such structures, but the behaviour of partially-saturated soils is not well characterised at the strain rates and stresses experienced in these events. In particular, little data is available for loose soils, whose compaction behaviour can have a substantial impact on structural stability and ballistic performance. This paper describes the use of split Hopkinson pressure bar experiments to characterise the pre- and post-saturation compressibility of a loose quartz sand at moisture contents of up to 15.0%. In contrast to dense soils, increases in moisture content between 0.0% and 7.5% led to a decrease in the stiffness of the sand. Above 7.5% moisture content, specimens reached full saturation during the experiment: the additional water had no further effect on the pre-saturation stiffness, but post-saturation behaviour was dominated by the stiffness of the pore water. Full saturation occurred at lower dry densities as moisture content increased, leading to a decrease in particle breakage. [ABSTRACT FROM AUTHOR]

In order to improve the internal quality of cross wedge rolling (CWR) shaft, the floating-pressure method (FPM) using high-pressure gas to compact void in CWR shaft is adopted in this paper. Firstly, the theoretical relations between each influencing factor and flow stresses are deduced by establishing the mechanical model of void closure based on FPM. Then, the laws of stress variation, metal flow, void shape variation, and microstructure evolution are all analyzed by DEFORM-3D finite element software, and the mechanism of void closure based on FPM is clarified. By means of hot isostatic pressing equipment, the FPM experiments are conducted, and it is illustrated that the outer dimensions of CWR shaft are hardly affected and its internal void can be effectively eliminated. Finally, the tests of specimens’ mechanics performance show that the tensile strength of the specimen is improved and its surface hardness is slightly reduced. The research results provide a new way for improving the yield and mechanical properties of CWR shaft. [ABSTRACT FROM AUTHOR]

The tolerancing integration in CAD model is among the major interests of most mechanical manufacturers. Several researches have been established approaches considering the geometrical and dimensional tolerances on the CAD modelers. However, the hypothesis of rigid parts is adopted in the digital mock-up. Thus, several physical factors are neglected; especially the deformations. In this regard, this paper presents a model for considering both tolerances and deformations in CAD model. The dimensional and geometrical tolerances are taken into account by the determination of assemblies configurations with defects basing on the worst case tolerancing. The finite elements (FE) computations are realized with realistic models. A method for modeling the realistic mating constraints, between rigid and non-rigid parts, is developed. Planar and cylindrical joints are considered. The proposed tolerance analysis method is highlighted throughout two cases study: the first comprises planar joints and the second comprises cylindrical parts in motion. [ABSTRACT FROM AUTHOR]

Stereo-DIC allows to track with a high accuracy the shape change and the surface displacement field of objects during deformation processes. When multiple camera arrangements are used, the shape and deformation measurement can be performed over the whole surface of the object. We submit that, in the case of intact specimens, with no internal defects and/or discontinuities, such boundary information can be used to estimate the internal displacement field by using proper interpolation functions. This calculation could serve, for instance, to evaluate the strain localization that occurs in metal specimens subjected to plastic deformation, hence allowing to get a better insight in the necking initiation and fracture propagation processes. In this paper, an interpolation method based on Bézier curves is developed and tested using simulated and real experiments on specimens with flat and cylindrical geometries. In particular, the deformation behaviour in the necking zone was investigated in the case of highly ductile and anisotropic materials. Numerical models were used to validate the method while the application to two real experiments demonstrated its feasibility in practical cases. The applicability of the method to more complex loading cases (e.g., bending, torsion, mixed-loads) or different initial shapes (e.g., curved beams, notches) will be investigated in future studies. [ABSTRACT FROM AUTHOR]

In the current work, an innovative fixture was designed and made to test local buckling of the notched plates under tensile loading. The conducted experimental measurements include the symmetric and for the first time the anti-symmetric modes of the buckling. Both monotonic and cyclic loading were applied on the specimens and the effect of the buckling on the fracture capacity and fatigue life of the specimens were investigated. The main interest of the paper is to describe the fixture and some experimental techniques. The buckling load was obtained from the tests as well as fracture capacity and fatigue life. Based on the obtained results, the buckling can reduce the fracture capacity as well as the fatigue life by 35% and 59%, respectively. Due to the mix mode of I-III, the anti-symmetric buckling shows a greater effect on the fracture capacity, however, the sliding crack closure due to mode III prevents the crack growth in the case of anti-symmetric buckling. [ABSTRACT FROM AUTHOR]

Instrumented indentation testing is widely used for the mechanical characterization of materials and phases. Among important mechanical parameters such as hardness and Young’s modulus the determination of yield stress and hardening behavior of metallic materials calculated from indentation results is a particular topical subject. This paper presents a methodology which allows for the reconstruction of the stress-strain curve from a single load-displacement curve measured by a spherical indenter. The method is based on the depth-dependent strain field induced by a spherical indenter. The loading part of the curve is discretised in single tuples of indentation depth and force. Since the mean strain induced by the spherical indenter is dependent on indentation depth, every depth can be assigned to a mean uniaxial strain value. The force is then used to calculate the associated uniaxial stress. The method was exemplarily applied to the carbon steel C45 in different heat treatment conditions. It could be shown that after a calibration procedure the stress-strain curves of the carbon steel can be calculated without the requirement of assuming a mathematical description of the curve (e.g. power-law material behavior). The method and its framework can easily be expanded and adjusted in order to be used as an easy and quick method for inverse determination of material parameters. [ABSTRACT FROM AUTHOR]

Thermal deformation is one of the principal factors that influence the machining accuracy of machine tools, and it can be improved by thermal error compensation. This paper presents a method of thermal error modeling using multisource information fusion, which can further improve the thermal error compensation accuracy. To set up a fusion model with optimal performance, two or more thermal error models should be established, from which a few models should be chosen to complement each other, and then combined into a synthesis model. In this paper, a dynamic thermal error model and a finite element model are combined to build a fusion model for lathe z-direction thermal error according to a fusion algorithm. The inputs for the fusion model are the values detected by the thermal sensors and the infrared imaging. An experiment carried out on a lathe verifies the validity of this modeling method. The results show that the multisource fusion model of thermal error can not only improve the prediction accuracy of thermal error over that of a single model, but also possesses better robustness. [ABSTRACT FROM AUTHOR]

Close range photogrammetry is becoming more popular as the availability and affordability of photogrammetry software increases and could be used to great effect in a number of civil engineering applications. Close range photogrammetry can be used to create detailed Digital Surface Models (DSMs) of objects that have deformed under applied loads. In addition to capturing the nature of the deformation, the deflection of the object subjected to load can be inferred from the same DSM. This paper presents an inexpensive method for measuring the deformation and displacement of corrugated steel cladding using a single digital camera and low cost software programs. The development of this method has been documented in detail, including an assessment of its accuracy which was determined to be ± 0.1 mm for a 142 mm × 350 mm section of corrugated cladding. In addition, this paper demonstrates how DSMs are particularly useful for evaluating the performance of a numerical model. The DSM created using photogrammetry was compared directly to the deformed mesh predicted by a numerical model, enabling an expansive and quantitative validation of that numerical model. It was found that the current numerical model of corrugated cladding can predict the deformation of the cladding under an applied load of 800 N to within 96 % of that documented during experiments. [ABSTRACT FROM AUTHOR]

The extruded large-scale thick-walled pipes made from Inconel 625 alloy are widely used in many fields such as in the oil and chemical industry, thermal power generation, nuclear power plant, aerospace, and defense industry. However, the nonuniform distribution of grain size along the thickness and length directions of the extruded pipe always appears, which has a great influence on the mechanical property and uniformity of the pipe. The inhomogeneous distribution of the exit temperature in the entire extrusion process is the decisive factor leading to the grain nonuniformity of the extruded pipe. Therefore, it is necessary but difficult to reveal the evolution of the exit temperature under some key extrusion parameters in order to effectively control the exit temperature uniformity. In this paper, a thermomechanical coupled finite element (TMC-FE) model, which can precisely predict the hot deformation behavior of the extrusion process for large-scale thick-walled Inconel 625 pipe, has been firstly developed based on the DEFORM-2D platform. And then, the influence of key extrusion parameters, namely extrusion speed ( V), initial billet temperature ( T), extrusion ratio ( λ), and friction ( μ), on the exit temperature was revealed by comprehensive simulations. In addition, using the standard deviation of exit temperature (SD) as the measure indicator of the exit temperature uniformity, we also disclosed the influence of the key process parameters on the exit temperature uniformity in detail. The results show that with the increase of V, T, and μ, the uniformity of exit temperature in the entire process firstly becomes better and then gets worse. The larger λ can result in a more uniform exit temperature. In consideration of the obtained results, within the feasible window of the key extrusion parameters defined in this paper, the conditions of T = 1,100-1,150 °C, V = 125-150 mm/s, μ = 0.015-0.02, and a larger extrusion ratio ( λ) are suggested for the extrusion of large-scale thick-walled Inconel 625 pipe in order to get more uniform exit temperature. [ABSTRACT FROM AUTHOR]

A thermal deformation prediction model of a high-speed motorized spindle is important for improving machining accuracy and reducing the thermal error in the spindle. The convective heat transfer coefficient reflects the internal heat exchange capacity of a motorized spindle. In the finite element thermal analysis of a motorized spindle, the heat transfer coefficient is used as the boundary condition to calculate the temperature field and thermal deformation. The accuracy of the convective heat transfer coefficient has the most evident effect on the thermal deformation prediction of the motorized spindle. In this paper, a method for optimizing the heat transfer coefficient based on the biogeography optimization algorithm is proposed for the 100MD60Y4 motorized spindle. The proposed method is used to develop a thermal deformation prediction model of an intelligent accurate motorized spindle. Accurate prediction of the thermal deformation of the motorized spindle is realized using the experimental data of the surface temperature of the motorized spindle. Experimental results show that the average prediction error after the optimization of the spindle bearing temperature is 0.22 °C. The average prediction error in the thermal deformation of the spindle is 0.72 μm. The developed model is more accurate compared with the conventional thermal deformation prediction model of the motorized spindle. [ABSTRACT FROM AUTHOR]

Slug rivet interference-fit riveting is one of the advanced connection technologies, which has been widely applied in aerospace manufacture. In the fields of residual stress analysis, structural deformation analysis, load transfer mechanism analysis, and the assessment of the effects of process parameters on riveting quality, study accuracy needs increasingly accurate and comprehensive models. Since the simulation of riveting process is a particularly time-consuming case. The aim of this paper is to develop some appropriate FE models for the special applications with a compromise between model size, calculation time, and simulation precision. Different types of FE models have been established based on force-controlled approach and displacement-controlled approach. The comparison between different FE models is satisfactory in terms of riveting process and riveting quality control criterion. The study significantly deepens the comprehension of the slug rivet installation process. Subsequent research can select an appropriate model according to its special target. The study will pave the way for further investigations. [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]

Analysis of the load distribution along raceways is fundamental for assessing dynamic and static capacity of the slewing bearings. In the literature, several finite element (FE) models have been proposed to estimate the load distribution and the deformation of slewing bearing. Although FE simulations are a useful tool for designers, there are a few experimental studies assessing accuracy and reliability of computations. In this paper, a FE model for a single-row four-point-contact slewing bearing is built in ABAQUS software. The key to the method is to simulate the balls under compression by traction-only nonlinear springs. Subsequently, the static loading experiment is designed: strain gauges are mounted on the inside circumference of the inner ring to obtain load distribution. The comparison between numerical and experimental results is discussed in detail. Remarkably, FE results are consistent with experimental data. [ABSTRACT FROM AUTHOR]

This paper presents the PullWorks software, an expert system that has been developed for the fast and simple design with the aim of optimizing the multi-stage copper wire drawing process. This software has been implemented applying the analytical method and complemented with the results of a series of experimental tests for the correct characterization of the processed material. The expert software system created has been used to model a real drawing line (Cunext Copper Industries S.L., Córdoba, Spain), with a production capacity of more than 30,000 t/year and an installed capacity of 1700 kW. PullWorks has made it possible to propose two modifications in the industrial process reducing its energy consumption by at least 1260 MWh/year: thanks to a reduction in the number of stages in the process lines (from 8 to 5, in the roughing line; from 19 to 13 in finishing) and by the elimination of the annealing treatment between them. The validity of these results has been verified through of the corresponding simulations made by the software Deform2D by means of which the numerical method of the finite elements analysis has been applied, and the solution was partially checked in the industrial process in operation. [ABSTRACT FROM AUTHOR]

The arch shape is a timeless structural solution as it has been widely used in the past but is still a common solution adopted nowadays for large spans. Structural efficiency depends primarily on optimal material exploitation, which allows us to minimize the structural volume. The paper is framed in the context of optimization of arch structures, and analytical design criteria are proposed, dealing with a specific class of deck bridges supported in the mid-span by arches. The investigation deals with a simplified structural scheme, constituted by statically determinate plane arches under self-weight and a single vertical load in the key section, exerted by the deck supports. The optimization criterion assumes a constant normal stress in all arch sections and the resulting arch shape is computed in closed form. Finally, the existence condition for the proposed solution is provided and some numerical examples are introduced. [ABSTRACT FROM AUTHOR]

Springback in sheet metal forming is a deformation that occurs when a workpiece is released from dies after forming. Prediction of springback using the finite element method (FEM) has been used in the design of stamping dies. The present paper describes an effective approach by which to improve the accuracy of springback analysis, which can also suppress the increase in the calculation time. In general, FEM using the analysis condition to decrease discretization errors greatly increases the computation time. The proposed procedure is as follows: (1) Quick analysis using a large mesh size is performed. (2) Data mapping and morphology mapping for the forming results are then performed using the database based on a detailed partial analysis of the drawbead and the die shoulder. (3) Springback analysis is performed using the forming results modified by the data mapping and morphology mapping. A forming experiment was conducted to confirm that the proposed method using the database greatly improves the prediction accuracy of the shape after springback and also suppresses the increase in calculation time. [ABSTRACT FROM AUTHOR]

This paper presents a general framework for modeling dynamic large deformation contact-impact problems based on the phantom-node extended finite element method. The large sliding penalty contact formulation is presented based on a master-slave approach which is implemented within the phantom-node X-FEM and an explicit central difference scheme is used to model the inertial effects. The method is compared with conventional contact X-FEM; advantages, limitations and implementational aspects are also addressed. Several numerical examples are presented to show the robustness and accuracy of the proposed method. [ABSTRACT FROM AUTHOR]

A polymeric gel is an aggregate of polymers and solvent molecules, which can retain its shape after a large deformation. The deformation behavior of polymeric gels was often described based on the Flory-Rehner free energy function without considering the influence of chain entanglements on the mechanical behavior of gels. In this paper, a new hybrid free energy function for gels is formulated by combining the Edwards-Vilgis slip-link model and the Flory-Huggins mixing model to quantify the time-dependent concurrent process of large deformation and mass transport. The finite element method is developed to analyze examples of swelling-induced deformation. Simulation results are compared with available experimental data and show good agreement. The influence of entanglements on the time-dependent deformation behavior of gels is also demonstrated. The study of large deformation kinetics of polymeric gel is useful for diverse applications. [ABSTRACT FROM AUTHOR]

The machining of micro thin-walled parts constitutes a key process in the microelectronic field. Deformations and machining errors easily occur, due to the low stiffness of micro thin walls. In this paper, a new iterative finite element method (iterative FEM) was proposed for the deformation predictions based on previous conducted works in the authors' laboratory. The new method, with aim at the effect of low radial immersion milling, was improved in three aspects compared to the traditional predicted methods: interaction calculation between the deformation extent and the cutting force; the grid division was significantly intensive; the cutting force was dispersed on certain nodes similarly to real cases. Firstly, the static deformation analysis and iterative FEM were introduced. Following, a diamond-coated micro milling tool was utilized to machine the micro thinwalled structures of 30 to 105 µm in thicknesses. Subsequently, several tungsten steel-coated milling tools were also utilized. Various tool diameters and edge radii were selected for comparison to the diamond-coated micro milling tool. The experimental results demonstrated that the deformations were approximately consistent with the simulation results, although certain errors still existed. [ABSTRACT FROM AUTHOR]

The two-roller straightening process has an irreplaceable position in the finishing process of metal bars. In this paper, the deformation of bar is macroscopically recognized by analyzing the deformation path in the roller gap. Graphic method and mathematical induction are adopted to analyze the deformation process of the section of bar. The equation of residual curvature and the unified equation of residual curvature are established. It is proved that although the initial curvature of each section of bar is different, the difference of initial curvature is eliminated by the reciprocating bending, and the process mechanism of the two-roller straightening is revealed. The speed of curvature unification is determined mainly by the ratio of plastic modulus to elastic modulus. The greater the ratio of plastic modulus to elastic modulus is, the slower the speed of curvature uniformity is, and the more the bending time required. Then, the quantitative analysis model and finite element model of the two-roller straightening process are established by taking the threesection constant curvature roller gap model as an example. The stress, strain, and straightness are discussed, and the variation of the elastic area ratio, the residual curvature, and the residual deflection with the bending time is quantitatively analyzed. The results verify the process mechanism of the tworoller straightening, and the design principle of roller shape is given. [ABSTRACT FROM AUTHOR]

Shot peen forming is often used to form the aerodynamic configurations of aircraft integral wing panels. The component is traditionally regarded as perfectly constrained target in peen forming process. However, weak-stiffness of the component results in concomitant macroscopic bending and stretching deformations, and releasing of peening stresses. Subsequent peening stresses are induced by shot impacts based on the current released stresses. In this paper, a intermittently peening-releasing finite element simulation model is used to study peening stress evolution in lowrigidity plate. An algorithm is proposed to calculate the increment of subsequent peening stress by connecting current stresses to the peening stresses in perfectly constrained target.With the algorithm, the peen forming deformations of freely constrained plates are calculated by equivalently simulating the peen forming process. And strip peen forming deformations are calculated and compared with experimental data. The comparison shows the peening deformation of a low-rigidity component should be treated as an incremental process and the algorithm can be used to predict the deformation with good accuracy. [ABSTRACT FROM AUTHOR]

The positioning error of ball screw feed drive systems is mostly caused by thermal deformation of the ball screw shaft in machine tool feed systems. This paper presents an adaptive real-time model (ARTM) for predicting the temperature transient distribution and thermal error distribution of the ball screw shaft. FEM integrated with the Monte Carlo method is applied to determining the heat generation rates of two bearings, moving nut and two guides in the ball screw feed system. Then based on the data of the FEM calculations, an exponential function of the feed velocity and time is used to describe variation of the temperature difference between the measured surface point and the center of the kinematical pair with time. Finally, a numerical forecasting algorithm is developed to predict the thermal characteristics of the screw shaft and its effectiveness is verified by the experiments. [ABSTRACT FROM AUTHOR]

Crystal plasticity finite element (CPFE) models that accounts for discrete micro-twin nucleation-propagation have been recently developed for studying complex deformation behavior of hexagonal close-packed (HCP) materials (Cheng and Ghosh in Int J Plast 67:148-170, 2015, J Mech Phys Solids 99:512-538, 2016). A major difficulty with conducting high fidelity, image-based CPFE simulations of polycrystalline microstructures with explicit twin formation is the prohibitively high demands on computing time. High strain localization within fast propagating twin bands requires very fine simulation time steps and leads to enormous computational cost. To mitigate this shortcoming and improve the simulation efficiency, this paper proposes a multi-time-domain subcycling algorithm. It is based on adaptive partitioning of the evolving computational domain into twinned and untwinned domains. Based on the local deformation-rate, the algorithm accelerates simulations by adopting different time steps for each sub-domain. The sub-domains are coupled back after coarse time increments using a predictor-corrector algorithm at the interface. The subcycling-augmented CPFEM is validated with a comprehensive set of numerical tests. Significant speed-up is observed with this novel algorithm without any loss of accuracy that is advantageous for predicting twinning in polycrystalline microstructures. [ABSTRACT FROM AUTHOR]

Non-uniform deformation in the thickness of tubular spun parts is a common problem in the flow forming process and has a significant impact on the performance of spun parts. In this paper, the plastic strain distribution in the wall thickness of tubular spun parts made of Haynes230 superalloy was obtained by the finite element method and microindentation hardness measurements. Moreover, the causes of the non-uniformity in plastic strain distribution were analysed, particularly the effect of main processing factors such as thickness reduction, feed rate and forming passes on plastic strain distribution in the thickness direction. The results indicate that the factors that have significant impacts on uniformity of deformation are thickness reduction and forming passes; deformation in the material is mainly concentrated in the outer layer of the spun part and less so in the inner layer. Furthermore, the plastic strain increases with an increase in thickness reduction, and the number of forming passes with the former process more favourably increasing the plastic strain in the inner layer than the latter. Therefore, in order to improve deformation uniformity in the spun parts, thickness reduction should be increased and the number of forming passes should be decreased when determining the total thickness reduction. This study is equally applicable to other materials. [ABSTRACT FROM AUTHOR]