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Abstract: CuCrZr alloys achieve high mechanical properties by thermal (e.g., supersaturated temper and aging), mechanical (e.g., ECAP), or thermomechanical treatments (solution annealing, cold working, and aging). This alloy can be considered a functional material, and it can be exploited in different application fields, thanks to a combination of thermal, electrical, and strength properties. In this work, tensile tests at different strain rates have been conducted on CuCrZr specimens produced by additive manufacturing. As-built and heat-treated conditions have been considered. The quasi-static tests have been performed by an electromechanical testing machine, while the high strain rate tests have been performed by a direct-tension split Hopkinson bar. The geometry of the samples has been selected based on the requirements of the dynamic tests, and the same geometry was used in quasi-static tests for the sake of comparison. High-speed imaging has been used to capture the real strain of the specimens. The results showed a limited positive strain rate sensitivity in terms of flow stress for as-built conditions, whereas negative strain rate sensitivity was observed for the heat-treated samples, but positive sensitivity in terms of ductility was observed for as-built, whereas uncertain results occurred in the case of heat-treated material.
Keywords: Additive manufacturing | CuCrZr alloy | High strain rate | Hopkinson bar | SLM
Abstract: The usual assumption made in mechanical characterization of soft biotissues with Atomic Force Microscopy (AFM) is that the specimen behaves as a purely elastic material. However, there is a limit indentation rate below which viscous effects can be neglected. A parametric study including about 200 FEM analyses shows that in the case of immature porcine zona pellucida (ZP) samples viscous effects become more significant for sharp tips. A linear relationship between the limit indentation rate and the geometry of the AFM probe is derived for the porcine ZP samples analyzed in this study.
Keywords: Atomic Force Microscopy | Indentation rate | Mechanical characterization | Probe geometry | Soft matter | Viscous effects
Abstract: Three-dimensional deformation analysis of human organs is very important from both diagnostic and therapeutic point of view. For example, comparing the deformation field in healthy and pathologic cardiac walls in the systolic phase allows to gather early and accurate information on the onset of heart diseases. MRI tagging is utilized in medicine to visualize with a great deal of detail the structure and morphology of tissues. The tagging process introduces a volumetric system of planes of reference similar to the process of introducing a grating in the 3-D moiré method in transparent media. The paper will analyze the kinematics of 3-D deformation fields and the fundamental concepts involved in 3-D deformation analysis within the restrictions imposed by the MRI method thus providing solutions for the inherent shortcomings encountered in the MRI tagging technique.
Keywords: Deformation of cardiac wall | Digital moiré | Large deformation analysis | MRI tagging | Rotations
Abstract: Quantification of 3-D deformations of human organs plays an important role in the understanding phenomena that have an impact in medical diagnosis and treatment of diseases. One important example is the mechanics of heart functions. Comparing normal deformation patterns of the cardiac cycle in healthy and diseased individuals can be a diagnostic tool that provides early and accurate indications of the onset of heart diseases. The tagging technique is an experimental mechanics method that makes it possible to utilize the extensive literature existing on the analysis of deformations utilizing the digital moire´ method for accurate and fast quantification of the heart 3-D kinematics. MRI tagging is an imaging technique used in medicine to visualize the structures of tissues of the human body in detail. MRI uses of the phenomenon of nuclear magnetic resonance to image tissues by exciting the nuclei of atoms in the tissue. Because of the different chemical composition of the tissues it can provide details that cannot be visible with CT Scans. By modulating magnetization it is possible to inscribe lattice-patterns in the tissue volume. These lattices are fixed to the under laying tissues for periods of time long enough to follow a cardiac cycle. The objective of this paper is to outline image processing techniques that can be utilized to decode the displacements and strains taking into consideration that one is dealing with large 3-D deformations that form a time sequence of images. These techniques are based on fundamental principles that have been developed in the field of digital moire´.
Keywords: Deformation of cardiac tissues | Digital moiré | Large deformations | MRI | MRI tagging
Abstract: The zona pellucida (ZP) is a specialized extracellular matrix surrounding the developing oocyte. This thick matrix consists of different types of glycoprotein, which have different roles in fertilization. Nowadays several techniques are developed and refined to establish the ZP mechanical response. The assumption at the basis of these methods is that the ZP behaves like an elastic body, dissipative forces are neglected, and thus the Young modulus value remains unaffected by probe dynamics. On the contrary dissipative force are strongly regulated by the slippage of ZP chains past one another whereas the absolute reaction force value is mainly due to the architecture of the ZP structure (number of cross-links and distances between knots). Elastic deflection is then due to the ability of each chain to stretch, whereas viscous flow is caused by the sliding of the molecules over one another. Therefore viscous reaction forces generated by the ZP have to be considered one of the main player in regulating the sperm transit but their peculiar behavior along the ZP structure is still poorly understood. In this context, for the first time, we developed and verified a visco-hyperelastic model able to reproduce the ZP reaction force stressed at different probe rate.
Keywords: Atomic force microscopy | Finite element analysis | Nonlinear optimization | Porcine zona pellucida | Prony series | Visco-hyperelasticity
Abstract: The umbilical cord is a peculiar and complex structure, about 50–60 cm in length and 1–2 cm in diameter, that is essentially composed of three vessels, i.e. the umbilical vein and two umbilical arteries, arranged in coils around the vein surrounded by a great amount of support tissue, the Wharton’s Jelly (WJ) that binds and encases the umbilical vessels. WJ is a mucoid connective tissue (5 % cells, 95 % extracellular matrix) described as a three-dimensional spongy network of interlacing collagen fibers and small woven bundles of glycoprotein microfibrils with an interdispersed soluble phase composed by hydrophylic hyaluronans and proteoglycans. WJ grants the protection of the umbilical vessels against compressive forces due to fetal movements and uterine contractions and is very important to guarantee venous and arterial umbilical blood flows. WJ response to mechanical loading is not well understood; another unsolved problem concerns WJ putative contribution to store and release the energy of the cardiac cycle, therefore in maintaining the anterograde flow in the cord arteries. This article presents a preliminary study on the mechanical behavior of umbilical cord. For that purpose, an optical set up based on intrinsic moire´ will be developed. Slices cut in the transverse directions of the cord will be submitted to equibiaxial tests and specimen deformations will be monitored in real time with moire´ by printing a grating on the cord slice. In this way, it will be possible to gather information on the mechanical anisotropy of the cord.
Keywords: Anisotropy | Biomaterials | Intrinsic moiré | Mechanical characterization | Umbilical cord
Abstract: Powering a remote wireless sensor is a challenging task if batteries are not suitable or enough capacious and their substitution is not feasible. In this project a remote wireless sensor is placed inside training shoes with the aim to collect and transmit data to evaluate and track the performance of an athlete. The primary energy source is the impact between the shoe and the ground while walking or running. The harvester has been designed by means of a multi-physics optimization based on an integrated electromagnetic-mechanical-electric-electronic simulator. Thus an automated optimization of the device with respect to volume constraints, magnets dimensions, induction coils placement and sizes and electric/electronic coupling have been performed to increase the average power extracted from the device at different speeds. These parameters are used as starting point for the product development phase in order to obtain a consistent number of prototypes and validate the simulations on these physical demonstrators. Finally, experimental outcomes evince the expected performance and a more than satisfactory agreement with the models, confirming the feasibility of the application.
Keywords: Design and optimization | Magneto-mechanical generator | Product development experimental application | Shoe mounted device
Abstract: Minimally invasive percutaneous fixation techniques play a role of crucial relevance in the clinical practice. In spite of their consolidated use, little is reported in the literature to provide a mechanobiological explanation on how design of fixation devices can affect the healing process within fractured vertebrae. The aim of the study is to develop a multi-scale mechano-regulation model capable of predicting how the patterns of tissue differentiation within a vertebral fracture change in the presence or in the absence of fixation devices and how the dimensions of the device, and the materials it is made from, can affect the outcome of the healing process. To this purpose, a multi-scale mechano-regulation model is developed that combines a macro-scale model representing the spinal segment L3-L4-L5 including the fractured body of the L4 vertebra, and a micro-scale model of a fractured portion of cancellous bone. The macro-scale model includes also a minimally invasive percutaneous fixation device. The above mentioned model allows us to investigate how spatial and temporal patterns of tissue differentiation in the fracture gap change for different dimensions of the fixation device components and for different materials (Ti-6A1-4V alloy and Co-Cr alloy). Furthermore, the model provides information on the stress state in the fixation device and hence allows the risk of failure of the device itself to be estimated. The mechanical properties of the forming tissue change as the healing process progresses. In order to validate the mechano-regulation model, displacement fields will be measured with moiré and holography and compared with numerical computations. The model predicts that fixation devices significantly shorten healing times. Increasing values of the rod diameter D and decreasing values of its radius of curvature R lead to shorter durations of the healing period. Manufacturing the rods in Cobalt-Chrome alloy is predicted to reduce slightly the healing period by providing greater mechanical stability within the fracture callus. © The Society for Experimental Mechanics, Inc. 2014.
Keywords: Mechanobiology | Minimally invasive percutaneous fixation | Moiré | Tissue differentiation | Vertebral fracture
Abstract: In the last few decades Experimental Mechanics, helped by advanced technologies to gather 3-D spatial information in non-transparent media, has evolved into a very general tool. It has become possible to observe the internal volume of engineering materials and in the area of biomechanics living internal tissues. This paper contains a brief review of Continuum Mechanics mathematical models that are available to formulate problems in 3-D including large deformations. The extension of the experimental methods that measure displacements in 2-D to 3-D is presented. Two important cases are considered: (a) use of deterministic signals, (b) use of random signals. In order to separate the complexity of the subject of 3-D analysis from the difficulties that arise from the use of random signals, the connection between mathematical models and their experimental determination is presented utilizing deterministic signals. The extension of the use of random signals to the determination of displacements in 2-D to 3-D is outlined. A new method to extract displacement information from random signals is developed and an example of application is provided. Two methods to extract displacement information in 3-D, the classical method based on displacement projections and discrete image correlation (DIC) based on following gradients of intensities are compared. There are many complex steps involved in data processing aside the basic approach, this circumstance makes difficult a comparison between the two methods, however it is possible to conclude that the results are in fair agreement. © The Society for Experimental Mechanics, Inc. 2014.
Keywords: 3-D continuum dynamics | 3-D continuum kinematics | 3-D displacement analysis discrete image correlation (DIC) | 3-D displacement measurement (deterministic, random signals) | Experimental 3-D displacement measurements opaque media | Large deformations
Abstract: In this paper experimental investigations of interference fit effects on the dynamic behaviour of assembled wheels are provided. The performed analyses on the automotive components take into account manufacturing pre-stresses and dimensional tolerances of mating parts. Experimental modal analysis is made on a set of components with identical nominal values to prove either the component or the assembly variability. For each mode a PCE-based meta model is developed upon a small sample of experimental observations and the interference fit level is estimated by means of the stress stiffening effect. The presented technique is aimed at improving the design and development of industrial components through the combination of established methodologies. The effectiveness of modal analysis, when combined with numerical/statistical approaches is pointed out.
Keywords: Design for modal assembly | Dimensional tolerances | Experimental modal analysis | PCE meta-models | Stress stiffening effect
Abstract: The dynamic properties of crossing and veering in coupled structures have been studied both numerically and analytically, but they are difficult to investigate using Finite Element Analysis because of the change in the topological arrangement due to the different configuration. Isogeometric Analysis, recently developed method for numerical simulation, could overcome some of the drawbacks of the change in the configuration such as remeshing, coupling between the nodes of the different models, need of a fine mesh to allow small change in the configuration to be comparable to the mesh size. The key of this method is to avoid meshing and using the same basis functions used by the geometry, namely Non-Uniform Rational B-Splines (NURBS), to define the discretization of a Finite Element model. Other advantages are the possibility of increasing the order of the functions to obtain smooth stress field across the element interfaces. An experimental test-rig composed by beams and masses, which allow different configuration and dynamic coupling as well, is used as test case to validate the accuracy of the results with respect to both experimental data and classical Finite Element Analysis.
Keywords: Crossing and veering phenomena | Isogeometric analysis | Modal analysis of coupled structure | Nitsche’s method
Abstract: Contouring of surfaces covers both metrology measurements and determination of displacements. There are a variety of scientific methods and corresponding devices used in contouring problems. Optical methods of contouring (OMC) have been proven to compete with the high precision and accuracy of Coordinate Measurement Machines (CMM). A general model of moiré contouring was recently developed by C.A. Sciammarella and his collaborators. The model integrates concepts of projective geometry and differential geometry of surfaces and utilizes symmetric projectors to reproduce the condition of projection from infinity. For specimens with dimensions ranging from few mm to more than 1 m, the measuring system and software provided standard deviations of the measured values that can reach 1/500 of the theoretical sensitivity defined by the pitch of the utilized grating. This paper will discuss the most recent trends in the optical contouring of surfaces focusing in particular on how to extend the general model of moiré contouring to the measurement of the three-dimensional displacement field of objects of arbitrary shape. © The Society for Experimental Mechanics, Inc. 2013.
Abstract: Powering a remote wireless sensor is a challenging task if batteries are not suitable or enough capacious and their substitution is not feasible. A remote wireless sensor can be placed inside a shoe with the aim to collect and transmit data to evaluate and track the performance of an athlete. The primary energy source is the impact between the shoes and the ground while walking or running. The harvester has been designed by means of a multi-physics optimization based on an integrated electromagnetic-mechanical simulator. Thus an automated optimization of the device with respect to volume constraints, magnets dimensions, induction coils placement and size have been performed to increase the average power extracted from the device at different walking speeds. Finally, prototypes of the optimal configurations demonstrate the predicted performance and a more than satisfactory agreement is evinced. © The Society for Experimental Mechanics, Inc. 2013.
Keywords: Electromagnetic generator | Energy scavenger | Magneto-mechanical | Optimization | Shoe mounted device
Abstract: This study represents a preliminary activity for the biomechanical numerical modeling aimed at the prediction of the human foot behavior and the deformation under different load conditions. It also represents the starting point to develop a scientific approach for the functional mass customization aimed at the optimization of comfort in footwear. Reverse Engineering (RE) methodologies developed for building up the external shape of the human foot are presented and discussed. Aim of this work is to study the problem of the digitalization of human feet under different conditions using three technologies: shape from stereo, from silhouette and from shading. The foot is one of the most difficult human parts to reconstruct taking into account the complex surface and the high curvature. In this article the disadvantage and advantage of each technique are analyzed. In particular tests about reliability and precision of the measure are considered. ©2010 Society for Experimental Mechanics Inc.
Abstract: Composite materials have increasingly become more common in ground transportation. As this occured thicker panels, as compared to composite panels used in aviation, become necessary in order to withstand high impact loads and day to day degradation. The effectiveness of these panels was often limited by the strength of the joint in which the panel was attached to the frame of the vehicle. Investigating methods of reducing strain concentrations within these joints would increase the effectiveness in using composite materials in ground transportation applications by increasing the load necessary for joint failure to occur. In this study, fiber optic strain gages were embedded in a composite panel along the bearing plane of a thick, single-lap, bolted joint. The gages allow for the strain profile above the hole to be determined experimentally. Several clearance values were then implemented in the bolt to determine their effect on the strain concentrations. Strain increased at every gage, by nearly the same proportion, when clearance was increased from zero to three percent. When clearance was further increased to five percent strain only continued to increase at gages three and four, with one and two remaining similar in value to what was seen at three percent clearance. Ultimately, like in thin composite panels, the zero percent clearance condition was the stiftest. ©2010 Society for Experimental Mechanics Inc.
Abstract: The use of polymeric and metallic foam sandwich panels in naval, aerospace, railway and automotive constructions is rapidly growing in the recent years because of technological improvements in manufacturing processes. However, it is still difficult to establish a direct relationship between the mechanical properties possessed by the panel and the specific manufacturing process. Mechanisms behind panel deformation, crack growth, fracture initiation and propagation still are not completely understood and therefore are intensively studied. In particular, structural behavior under compression is a critical issue also in view of the lack of official standards on foam core sandwich panels. This work aims at studying mechanical properties of high density polyethylene foam core sandwich panels produced by rotational molding. These panels can be built without using adhesives as the polyethylene foam grows inside mold and then adheres to facesheets while material still is at high temperature. In the present study, polyethylene foam panels of different thickness are tested under edgewise compression loading. The resulting out-of-plane deformation is then monitored in detail with a projection moiré setup including two projectors and one camera.
Abstract: Thin film technology is an area of great importance in current applications of opto-electronics, electronics, MEMS and computer technology. A critical issue in thin film technology is represented by residual stresses that arise when thin films are applied to a substratum. Residual stresses can be very large in magnitude and may result in detrimental effects on the role of the thin film must play. For this reason it is very important to perform "online" measurements in order to control variables influencing residual stress. The research work presented in the paper represents the first step towards the practical solution of such a challenging problem. A methodology to measure residual stresses utilizing reflection/projection moiré interferometry to measure deflections of thin coated specimens is developed. Results are in good agreement with experimental values provided by well established measurement techniques. A special optical circuit for the in situ measurement of residual stresses is designed trying to satisfy the constraints deriving from the tight geometry of the vacuum system utilized to carry out the deposition.
Abstract: This study discusses the application of a hybrid experimental-numerical approach to analyze nano-indentation curves of a biological membrane acquired with an Atomic Force Microscope. The proposed procedure combines experimental measurements, FEM analysis and numerical optimization and is completely general. Variations of estimated Young modulus of the membrane are determined when attributing different constitutive laws to the sample and in the case of progressive blunting of the AFM tip during the measurement. Since traditional analysis of Atomic Force Microscope indentation curves relies on an inappropriate application of the classical Hertz theory, a comparison between the hybrid approach and the Hertzian model in the determination of the elastic properties of the sample is presented. In particular, it is found that large errors occur in the derivation of the Young modulus when the Hertzian model is used for the analyis of experimental data.
Abstract: This paper presents a very compact electro-mechanical wideband energy harvester optimized for tire applications. The energy conversion process of the device takes into account the simulation of different phenomena like: non linear dynamic and adaptive resonant behavior of the seismic mass, electromagnetic and magneto-static coupling between floating magnetic mass and coils, transfer of the generated power to an external load by means of a nonlinear circuit interface. The paper is focused on the pneumatic effects of the floating magnet sliding into a calibrated guide. A convenient choice of clearance between moving and fixed parts can be used to create an effective air brake preventing or softening shocks with end stops and to modify system dynamic. A block-oriented Simulink®, experimentally validated, model has been realized to predict scavenger device performance and to optimize design parameters. Equivalent linearized stiffness and damping factors due to pneumatic effects have been modeled in the lumped parameters system to get a simplified model and to formalize relations with the geometrical characteristics. Analysis of the effect of several nonlinearities at different vehicle speed have been performed.
Keywords: Adaptive resonance | Electro-mechanical device | Energy scavenger
Abstract: The main purpose of the present study was to optimize a prototype hexapod robot, called Gregor I, through reverse engineering techniques. The robot is based on experimental observations of the cockroach with regard to mechanical design and the locomotion control strategy. This paper reports on the design phase of a hexapod robot, where the basic geometry of the system is defined through solid modeling and improved through kinematic and dynamic studies, using multi-body software. The dynamic simulation environment made it possible to study the performance of the system under different working conditions. Guidelines for an optimization process of the hexapod structure were drawn from these analyzes, aimed at the improvement of specific characteristics: speed, payload and climbing capabilities. Finally, the robot model and the robot prototype were compared.
Abstract: Defining a procedure for the characterization of the crankshaft and entire engine unit, based on CAD-FEM multi-body methodology, would provide an analysis tool which avoids the simplified hypotheses usually accepted when designing these components. The methodology is based on the Craig-Bampton method, i.e. on the theory of component mode synthesis. According to the Craig-Bampton theory, the deformation of a flexible crankshaft interfacing with the rest of the engine is obtained through static and normal modes, considering the discretized model with a large number of degrees of freedom and using modal truncation. It is based on the separation of interface and internal d.o.f. Using modal stress analysis has the advantage of reducing the d.o.f. of the FEA model. The multi-body model includes the elasticity of the camshaft and the reduced inertia of the gearbox and timing system. Comparing simulations performed at different engine speeds, the crankshaft evidenced the angular oscillations of generic sections of the axis and shaft, without separating the bending and torsional d.o.f. At higher engine speeds, the vibrational response showed how the harmonics with greater amplitude correspond to the crankshaft's first natural modes and are excited by some harmonics present in the engine moment.
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