In recent years, the development of high-strength steels such as multi-phase TRIP (transformation-induced plasticity)-aided steels have shown great promise due to their excellent combination of high strength and ductility. In this paper, the effect of strain-induced martensitic transformation on mechanical properties is studied. Uniaxiale tension tests at different strain rate (10, 15 and 20 mm / min) are conducted at 25° C in order to characterize the mechanical behavior of AISI 304L. The microstructure, particularly retained austenite, is analyzed using optical microscopy, Vickers hardness measurements. The results showed that all properties measured are increased from (Re=390.96MPa to Re=425.96MPa and Hv=300.94Hv to 343.51HV). Secondly, the influence of the annealing treatment on microstructure and mechanical properties of the joint formed by the spot welding are characterized using tensile test, metallographic analysis and Vickers hardness measurements.

The evaluation of cable robot performances cannot neglect the considerable limitations introduced by cable tension bilateral bounds, i.e. the fact that neither negative nor limitless cable forces can be exerted. Therefore, such constraints must be explicitly accounted for and the indexes typically employed for parallel robots cannot be employed straightforwardly. In this work, instead of proposing a new performance index, we introduce an approach to performance evaluations which is based on the computation of the maximum force, along a specific direction, which can be exerted by the cables on the moving platform of a fully actuated or redundant cable robot. Such a computation, once extended to the whole workspace of a robot or, if needed, to any direction, openly and effectively describes the robot performances and can be extremely useful in practice. The application of the method to two fully actuated and fully constrained planar cable robots, together with a comparison with popular performance indexes, gives evidence of the method effectiveness.

In synchronous belt drives, transmission error is generated due to resonance of the belt spanning the driving and driven pulleys when the transverse natural frequency of the belt approaches the meshing frequency of the belt and the pulley teeth. The behavior of the transmission error caused by resonance has been assumed to be dependent on the installation tension. In the present study, the influence of installation tension on the transmission error in a synchronous belt drive was experimentally investigated for a case in which first mode vibration due to resonance was induced in both the upper and lower spans. In addition, an analysis of the transmission error based on the experimental results was carried out. A transmission error contains two components: one with a period equal to the pitch of the pulley, and the other with a period of half the pulley pitch. Good agreement was found between the calculation and experimental results, thus confirming the validity of the analysis method. For a fixed pulley speed, the transmission error was largest when the installation tension was applied at a position where the displacement of the upper span was equal to that of the lower span. When the installation tension was varied and the pulley speed was adjusted so that the belt experienced resonance, the transmission error decreased with an increase in installation tension.

This investigation is focused on the dynamic response of some commercially available piezoelectric materials which will be incorporated into textile materials for vibration control with a view of sports brassiere. Ceramic-based piezoelectric fiber composites (PFC), piezoelectric fiber composite bimorph (PFCB) and polymer-based polyvinylidene fluoride (PVDF) of various thicknesses have been chosen for this investigation. In a typical experiment, one end of each of the piezoelectric strips is fixed to the vibration table of an electrodynamic exciter while the other end is terminated at the cross-beam of a very stiff frame. The strip is placed under tension and made to undergo base excitation using pseudo-random signal from (0–2000) Hz using the electrodynamic shaker. The force output response is obtained using force transducers. The characterization of these piezoelectric materials will determine their behavior when embedded in the textile material for sports brassiere application.

Cadaveric experiments and computer simulations have shown that the tendon network of the fingers performs logic computation to preferentially change torque production capabilities. Distribution of input tensions in the tendon network itself regulates how tensions propagate to the finger joints, acting like the switching function of a logic gate. The tendon network as proposed by Winslow (1669–1760) is responsible for this phenomenon; and that a certain switching behavior is exhibited, depending upon the input tension loading. This work explores how this switching behavior varies with different static postures of the finger and under different loading conditions on input tendon terminals. Experimental setup is designed and developed to study this switching behavior, comprising of a bio-mimetic model of middle finger, designed and developed. Winslow’s tendon network as proposed by Winslow is employed over it. Force sensors based on strain gauges are designed and developed in order to measure the tension at the proximal and terminal slips of network. Experiments have been carried out to understand the switching behavior exhibited by rhomboidal tendon network and how it varies under different loading conditions. Its variation with different pre-configured postures under static equilibrium is observed. Results show that indeed the rhomboidal tendon network of Winslow exhibits switching behavior and that they vary under different loads and postures of the finger.

Graded materials, also known as functionally graded materials (FGMs), are multiphase composites mainly composed of a ceramic and a metal; thus, they exploit the heat, oxidation and corrosion resistance typical of ceramics, and the strength, ductility and toughness typical of metals. These materials are mainly used as heat barriers. In addition, many of the present and potential applications of FGMs involve contact problems. On the other hand, the production process of FGMs is somewhat complex and leaves some defects in the produced structure. One of the most important defects in such structures is surface cracks. Here, the combination of the contact and crack problems is investigated in a functionally graded rectangular plate containing a semi–elliptic surface crack indented by a frictionless rigid spherical indenter. The plate is simply supported and the crack is located in the middle of the plate surface in the tension part. The crack surface is parallel to one of the plate edges. The gradient of mechanical properties variation is considered through the thickness of the plate and the volume fraction distribution of the constituting phases is modeled by a polynomial function and the Poisson’s ratio is kept constant. The analyzing of the problem is divided into two steps. At the first step, for an uncracked plate the equations of equilibrium are derived in terms of the displacement field and are solved numerically to find the contact rule. As the second step in studying the problem, the contact problem of a cracked plate is modeled by using ABAQUS finite element package. The aim of this step is to find the effect of the presence of the crack on the contact rule. The optimum mesh for the ABAQUS model is found by using the results of the first step. In order to do so, an ABAQUS model is created for the uncracked plate. The analytical results and the obtained results from ABAQUS for specified plate and indenter dimensions and material properties are compared. After finding the optimum mesh, a crack is added to the ABAQUS model of the plate under contact loading. The effects of gradient changes and indenter dimensions on the contact rule and stress distribution at the crack tip are then investigated by using the obtained ABAQUS model. The acquired results show that the influence of the material nonhomogeneity on the stress distribution around the crack tip and in the plate (uncracked and cracked) and contact rule can be quite significant. In general, increasing the overall volume fraction of the metal phase increases the load carrying capacity in an uncracked plate. In a cracked plate, the changes in material distribution as well as the changes of the indenter diameter does not affect the results that much.

Medical surgery is currently rapidly improving and requires modeling faithfully the mechanical behavior of soft tissues. Various models exist in literature; some of them created for the study of biological materials, and others coming from the field of rubber mechanics. Indeed biological tissues show a mechanical behavior close to the one of rubbers. But while building a model, one has to keep in mind that its parameters should be loading independent and that the model should be able to predict the behavior under complex loading conditions. In addition, keeping physical parameters seems interesting since it allows a bottom up approach taking into account the microstructure of the material. In this study, the authors consider different existing hyperelastic models based on strain energy functions and identify their coefficients successively on single loading stress-stretch curves. The experimental data used, come from a paper by Zemanek dated 2009 and concerning uniaxial, equibiaxial and plane tension tests on porcine arterial walls taken in identical experimental conditions. To achieve identification, the strain energy function of each model is derived differently to provide an expression of the Cauchy stress associated to each loading case. Firstly the parameters of each model are identified on the uniaxial tension curve using a least squares method. Then, keeping the obtained parameters, predictions are made for the two other loading cases (equibiaxial and plane tension) using the associated expressions of stresses. A comparison of these predictions with experimental data is done and allows evaluating the predictive capabilities of each model for the different loading cases. A similar approach is used after swapping the loading types. Since the predictive capabilities of the models are really dependent on the loading chosen to determine their parameters, another type of identification procedure is set up. It consists in adding the residues over the three loading cases during identification. This alternative identification method allows a better agreement between each model and the various types of experiments. This study evaluated the ability of some classical hyperelastic models to be used for a predictive scope after being identified on a specific loading type. Besides it brought to light some existing models which can describe at best the mechanical behavior of biological tissues submitted to various loadings.

It is well known that the use of inelastic constitutive equations accounting for induced softening leads to pathological space (mesh) and time discretization dependency of the numerical solution of the Initial and Boundary value Problem (IBVP). To solve this drawback a thermodynamically-consistent formulation incorporating first gradient of micromorphic damage in the framework of micromorphic continuum is proposed. In this formulation the damage field is strongly coupled with mixed isotropic and kinematic nonlinear hardening together with micromorphic damage variables. A new finite element with one additional degree of freedom for the micromorphic damage field is developed and implemented into ABAQUS/EXPLICIT using the user’s subroutines VUEL and VUMAT. For the validation purpose, 3D uniaxial tension example of metallic sheet is performed using the proposed micromorphic fully coupled elastoplastic constitutive equations.

This paper investigates the dynamic stability of an axially moving web which translates with periodically varying speeds and is subjected to partially distributed tensions on two opposite edges. The web is modeled as a rectangular plate simply supported at two opposite edges where the tension is applied, and free at the other two edges. The plate is assumed to possess internal damping, which obeys the Kelvin-Voigt model. The moving speed of the plate is expressed as the sum of a constant speed and a periodical perturbation with a zero mean. Due to the periodically varying speed of the moving plate, terms with time-dependent coefficients appear in the equations of motion, which may bring about parametric instability under certain situations. First, the in-plane stresses of the plate due to the partially distributed edge tensions is determined exactly by the theory of plane elasticity. Then, the dependence on the spatial coordinates in the equations of motion is eliminated by the Galerkin method, which results in a set of discretized system equations in time. Finally, the method of multiple scales is utilized to solve this set of system equations analytically if the periodical perturbation of the moving speed is much smaller as compared with the average speed of the plate, from which the stability boundaries of the moving plate are obtained. Numerical results reveal that only combination resonances of the sum-type appear between modes having the same symmetry class in the transverse direction. Unstable regions of main resonances are generally larger than those of sum-type resonances.

In industrial plants some parameters can not be evaluated properly or they are varying with time. These parametric uncertainties has to be taken into account during the design process of industrial systems. In this work, the developped optimization approach is applied on an industrial roll-to-roll sytem. Such systems are commonly used to handle materials as polymer, metal, paper and textile. The key challenge is to move the web at the expected speed while maintaining the web tension in an acceptable range around its reference. Moreover, the Young’s modulus of the web is difficult to evaluate and it is varying with time due to temperature and moisture variations. This paper deals with the web tension controller synthesis on a large-scale roll-to-roll system with uncertain Young’s modulus. To synthesize web tension controllers, an H∞ approach is applied and adapted to the system with parametric uncertainties using multi-objective robust design optimization.

The paper deals with the effect of stress state on inelastic deformation and failure behavior of ductile solids. The continuum model takes into account stress-state-dependence of the damage and failure criteria with different branches corresponding to different micro-mechanical mechanisms depending on the stress triaxiality and the Lode parameter. Basic material parameters are identified using various tests with smooth and differently notched tension and shear specimens. To get more insight in the complex damage and failure mechanisms on the micro-scale additional series of three-dimensional micro-mechanical numerical analyses of void-containing unit cells have been performed. These calculations cover a wide range of stress triaxialities and Lode parameters in tension, shear and compression domains. The numerical results are used to discuss general trends, to develop equations for the damage and failure criteria, and to identify corresponding parameters of the continuum model.

Relatively large, alternating in time, operational deformations of distributed piezoelectric actuators used in active vibration control may create a hazard of material degradation and damage of the actuator/host structure coupling. In the presented study a beam-like system with a surface mounted piezoelectric sensor/actuator pair operating in a closed loop with velocity feedback is analysed. The applied actuator is a piezoelectric fiber composite (PFC) with PZT (lead-zirconate-titanate) fibers aligned and polarized longitudinally. The uniform field method based on the rule of mixtures is used to determine the effective properties of the piezocomposite. Two types of the actuator failure are taken into account. The first relates to the edge delamination modelled as a significant reduction of the adhesive interlayer shear stiffness. The second relates to the PFC material degradation, which is regarded as a softening of the matrix material surrounding PZT fibers. It is assumed that the damaged adhesive region of the constant shear stiffness extends uniformly across the actuator from its ends to the centre. In analysis the beam is divided into sections due to its geometry, external loading and the damaged regions supposed. The governing equations of the activated beam sections are coupled equations related to the electrically induced tension/compression of the actuator and bending of the beam, respectively. The obtained steady-state solution satisfies boundary conditions and continuity conditions at the borders of the beam and the actuator sections. Results of calculations show the effects of stiffness degradation of both the bonding interlayer and the piezocomposite matrix material on the beam deflection and transmitted shear stresses. Besides, dynamic responses of the active system regarding changes of the control effectiveness are numerically investigated and discussed.

Accumulators are used in industrial elastic web processing plant such as paper, mills, fabric, rolling mills, to permit rewind or unwind core changes while the process continues at a constant velocity. The objective is to maintain constant web line velocity and tension into and downstream the accumulator. This paper presents a summarize of nonlinear models of different classical industrial accumulator structures: one with a pneumatic actuated carriage and one with a motorized carriage. These models are derived from physical laws that describe web tension and velocity dynamics in each web span. A second part presents new accumulator structures enabling performances improvement, considering the accumulator output web tension. Finally, the last part of this paper compares, by simulations in Matlab/Simulink software environment and using performances criteria, the performances of optimized accumulators and classical industrial ones.

Effect of Stone-Wales percentage defect on effective elastic modulus of single-walled carbon nanotubes (SWCNT) is investigated. The Stone-Wales defect is a crystallographic defect that happens in nanotubes and is believed to affect the nanotubes mechanical properties. In order to calculate the mechanical properties of SWCNTs under axial tension, molecular dynamics (MD) simulations using the Morse potential is performed. An in house FORTRAN code is developed and utilized. The Young’s modulus of the perfect SWCNTs and those with different defect percentage is obtained using the classical elasticity theory. It is observed that for low percentage of defect (less than 8%) as the diameter increases the Young’s modulus of SWCNTs slightly increases. However, for high percentage of defect (more than 8%) as diameter increases the Young modulus clearly decreases.

This contribution presents the experimental investigations on design and fabrication of the dorsal fin of the shark robot-fish mechanism which is controlled using NiTi Shape Memory Alloy (SMA) actuators by a Fuzzy controller. The dorsal fin helps the shark not only to turn around, but also it helps shark to roll. This fin contains two main parts, a rigid part; is connected to the shark’s body and another part is mounted on the latter one which can be rotated. The rotation angle of the second part is controlled by two parallel SMA wires. The subtlety of this installation is the tension of the right wire, when the left one is actuated. In addition, a fuzzy controller was determined by considering the characteristics of the SMA wires and designated mechanism which has hysteresis response characteristics against heating and cooling.

This paper presents a method for the calculation of the stresses around three non-intersecting identical circular holes in a row, in a thin and infinite isotropic plate subjected to in-plane longitudinal, transverse or biaxial tension at infinity. The calculation of the stresses around any of the three holes is obtained in terms of the stresses that would exist around and at the center of the contour of a third would-be hole in the plate, initially, containing two holes. The results from the present method are compared to finite element as well as to published results in the literature. It is seen that the method yields satisfactory results at key points around the contour of the holes.

Acoustic emission (AE) has been known as an excellent technique to monitor crack propagation and fracture mechanism. For more domination on AE behavior of materials, comprehensive knowledge on effective parameters is necessary. Heat treatment as one of the important factors on AE characteristics of a material must be considered. This investigation is primarily aimed at studying the effect of tempering heat treatment on characteristics of acoustic emission signals monitored during tension tests of a cold-work tool steel. Single edge notched samples of AISI D2 cold-work tool steel were prepared. Then, respectively annealing, austenitizing and tempering were performed. Tempering was carried out at 5 different temperatures from 0 to 575 C. Finally, samples were loaded at tension and AE signals recorded synergistically. Analyzing of the characteristics of AE signals showed that: (a) In all tempering conditions, the AECC increases slowly at the beginning and rapidly at the point of crack growth, although at higher tempering temperatures we have gradual rise in AECC plot; (b) Increasing tempering temperature, average value of AE count number, amplitude, energy and peak frequency decreases; (c) At 525 C, because of secondary hardening, average value of investigated AE parameters increase strongly and (d) analyzing the relation between fracture mode, AE characteristics and tempering temperature showed that special AE behavior of specimens tempered at 525 C is because of the transformation of retained austenite in ferritic matrix.

The Institute for Product Development and Mechanical Engineering Design (PKT) at the Hamburg University of Technology (TUHH) is developing a new generation of Stirling motors for small combined heat and power plants up to a range capacity of 5 kW mechanical power output. Main objective of the project is to increase the efficiency of the Stirling motor. Reducing friction, wear and heat conductivity are the key benefits for the application of ceramic components in high loaded tribological contacts; furthermore the principle of the Stirling motor requires a lubricant free gas circuit. The applied systematically design process, based on product functions and active principles allows a target-oriented development of concepts for all components and assemblies of the Stirling motor. No simple substitution of metallic into ceramic components has been taken place, but rather a “design for ceramic” has been applied to use advanced ceramic materials in an optimal manner. Before manufacturing a prototype of the Stirling motor, mechanical tests of the main tribological contacts are intended. For these tests the authors’ institute will use two existing test rigs, the NPT (non-proportional tension-torsion test) and the MPH ( M echanische P ru¨fung von H ydraulikflu¨ssigkeiten–Mechanical Testing of Hydraulic Fluids) to investigate strength, friction and wear of the ceramic components. Within this paper at first a brief overview of the Stirling motor principle and the functions of the key components will be given. Based on this and from the tribological point of view the main requirements of the motor parts will be derived. The description of the developed motor concept with ceramic as a high temperature material will be the main part of the paper, followed by the description of the intended rig tests to analyse strength, friction and wear behaviour of the chosen ceramic materials.

The 9–12%Cr martensitic steels are candidate materials for several components of the generation IV and fusion nuclear reactors. In these future applications, in addition to long holding periods, cyclic loadings corresponding to start and stopoperations and maintenance must also be taken into account. Creep-fatigue interactions must therefore be considered to design these components. A broad literature review showed that between 20°C and 650°C the fatigue lifetime of these materials followed a unique Manson-Coffin law. Adding a stress-relaxation holding period significantly reduces the fatigue lifetime for total strain lower than Δε t = 0.7%. For higher strain ranges, no significant effect of holding period exists anymore. Moreover, several studies reported a more deleterious effect of compressive hold times compared to tensile holding periods. Additional tests and detailed observations of the damage mechanisms responsible for fracture of pure fatigue, relaxation-fatigue and creep-fatigue tests were carried out on a 9 Cr − 1 Mo modified steel tested at 550°C in air. This material showed a strong work softening effect. The cyclic plastic behavior of the material was studied using an enhanced stress partitioning method to evaluate the kinematic, isotropic and viscous parts of the cyclic stress. It was concluded that in all the cases the observed softening effect was mainly due to the kinematic stress decrease [1]. The effect of a tensile or compressive hold time on fatigue life was also investigated [2, 3]. The deleterious effect of compressive hold times was thus confirmed. No creep cavitation was observed and the fracture was due to the propagation of transgranular fatigue cracks. Two distinct damage mechanisms were identified, depending on the strain range and the hold time : (i) crack initiation occurred due to usual Stage I extrusions/intrusions mechanisms leading to the propagation of a bifurcated crack; (ii) multiple cracks were initiated from the brittle fracture of the oxide layer formed at the free surface of the specimens. It was shown that this oxide failure leads to a penetration of oxygen along the microstructural boundaries enabling the cracks to propagate. Oxide layers grown during tensile (compressive) holding periods are mainly loaded in compression (tension) during the fatigue cycle. The critical strains necessary to crack oxide layers are lower for tensile loading (i.e. compressive holding periods) as shown by finite element and analytical calculations. Therefore compressive holding periods leads more easily to the second and more severe damage mechanism [2, 3]. A model, identified on short crack propagation tests and from experimental endurance curves, gives excellent predictions in pure-fatigue [4]. In creep-fatigue the predicted lifetimes are in the usual range [N exp /2, 2N exp ] for all strain amplitudes and hold times. In addition, complex phenomena, such as the deleterious effect of compressive holding periods are also reproduced. An attempt is made to show how this model can be extrapolated in temperature to longer hold times.

Nickel-Titanium, commonly referred to as Nitinol, is a shape-memory alloy with numerous applications due to its superelastic nature and its ability to revert to a previously defined shape when deformed and then heated past a set transformation temperature. While the crystallography and the overall phenomenology are reasonably well understood, much remains unknown about the deformation and failure mechanisms of these materials. These latter issues are becoming critically important as Nitinol is being increasingly used in medical devices and space applications. The talk will describe the investigation of the deformation and failure of Nitinol using an in-situ optical technique called Digital Image Correlation (DIC). With this technique, full-field quantitative maps of strain localization are obtained for the first time in thin sheets of Nitinol under tension. These experiments provide new information connecting previous observations on the micro- and macro-scale. They show that martensitic transformation initiates before the formation of localized bands, and that the strain inside the bands does not saturate when the bands nucleate. The effect of rolling texture, the validity of the widely used resolved stress transformation criterion, and the role of geometric defects are examined.