The purpose of this study is to compare the shear bond strength of different resin bases and artificial teeth made of ceramic or acrylic resin materials and whether tooth-base interface may be treated with aluminium oxide sandblasting. Experimental measurements were carried on 80 specimens consisting of a cylinder of acrylic resin into which a single tooth is inserted. An ad hoc metallic frame was realized to measure the shear bond strength at the tooth-base interface. A complete factorial plan was designed and a three-way ANalysis Of VAriance (ANOVA) was carried out to investigate if shear bond strength is affected by the following factors: (i) tooth material (ceramic or resin); (ii) base material (self-curing or thermal-curing resin); (iii) presence or absence of aluminium oxide sandblasting treatment at the tooth-base interface. Tukey post hoc test was also conducted to evaluate any statistically significant difference between shear strength values measured for the differently prepared samples. It was found from ANOVA that the above mentioned factors all affect shear strength. Furthermore, post hoc analysis indicated that there are statistically significant differences (p-value=0.000) between measured shear strength values for: (i) teeth made of ceramic material vs. teeth made of acrylic resin material; (ii) bases made of self-curing resin vs. thermalcuring resin; (iii) specimens treated with aluminium oxide sandblasting vs. untreated specimens. Shear strength values measured for acrylic resin teeth were on average 70% higher than those measured for ceramic teeth. The shear bond strength was maximized by preparing samples with thermal-curing resin bases and resin teeth submitted to aluminium oxide sandblasting.

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 zona pellucida (ZP) is a specialized extracellular matrix surrounding the developing oocyte. This thick matrix consists of various types of glycoprotein that play different roles in the fertilization process. Nowadays, several techniques are available for assessing ZP’s mechanical response. The basic assumption behind these methods is that the ZP behaves like an elastic body: hence, dissipative forces are neglected and Young’s modulus remains unaffected by probe dynamics. However, dissipative forces are strongly regulated by the slippage of ZP chains past one another while reaction forces related to elastic deformations (driven by the ability of each chain to stretch) depend on the ZP structure (i.e. number of cross-links and distances between knots). Although viscous reaction forces generated by the ZP are one of the main factors regulating sperm transit, their peculiar behaviour along the ZP structure remains poorly understood and rarely investigated. In order to overcome this limitation, a novel visco-hyperelastic model describing the porcine ZP reaction forces generated by nanoindentations at different probe rates is developed and verified in this study. Visco-hyperelastic parameters of porcine ZP membranes are determined by means of a hybrid characterization framework combining atomic force microscopy nanoindentation measurements, nonlinear finite-element analysis and nonlinear optimization. Remarkably, it is possible to separate the contributions of hyperelastic and viscous terms to ZP mechanical response and evaluate the error made in the determination of ZP mechanical properties if viscous effects were not considered.

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.

Nanoindentation has recently emerged as a powerful tool for measuring nano- and microscale mechanical properties in tissues and other biomaterials. This technique has been used to measure the mechanical properties of microstructural features in cells, biopolymer networks, and complex biomaterials. Despite the wide use of the nanoindentation, the residual stress effect in the determination of soft samples elastic properties is still poorly explored. By using parametric finite element analysis and atomic force spectroscopy, we determined the relationships between residual stress and indenter geometry and how it can affect the structural response of polymeric spherical shells flattened on a hard surface.

The Big BangBig Crunch (BBBC) optimization method is a recently developed meta-heuristic algorithm that mimics the process of evolution of the universe. BBBC has been proven very efficient in design optimization of skeletal structures but yet computationally more expensive than classical meta-heuristic algorithms such as genetic algorithms and simulated annealing. To overcome this limitation, the paper presents a novel hybrid formulation of BBBC where the meta-heuristic search is hybridized by including gradient/pseudo-gradient information as a criterion to perform new explosions. Each new trial design is formed by combining a set of descent directions and eventually corrected in order to improve it further. The new BBBC algorithm is successfully tested in two classical weight minimization problems of a spatial 25-bar truss and a planar 200-bar truss.

Thin-walled elements are widely utilized in the design of aerospace structures as they allow to obtain lightweight structures. However, while the structures so designed may be sufficient to carry the in-plane tensile loads and satisfy strength requirements, they are often prone to fail under buckling induced by compressive or shear loads. Buckling is a highly non-linear phenomenon caused by the sudden conversion of a large amount of in-plane strain energy into bending strain energy [1]. This process may be expressed in different modes. For example, global buckling is said the catastrophic collapse of the entire structure; local buckling affects a portion of the skin; stiffener buckling occurs in correspondence of stiffener segments. Other “special” buckling modes are typical of sandwich structures (wrinkling, dimpling, etc.). In order to guarantee structural safety against buckling, reinforcing elements (stiffeners) running in the longitudinal and transverse directions are added to the panel skin to increase the stiffness of the structure. The proper selection of the stiffening configuration and materials leads to minimize structural weight thus maximizing payload. A number of trade studies on the sensitivity of structural weight of stiffened panels to parameters such as stiffener geometry, materials, and type of construction and manufacturing methods were presented in literature (see for example, [2,3]). Design concepts are usually compared and preliminarily selected to be further developed later on the basis of their structural weight (typically, the weight per unit area) which is minimized by means of optimization methods. Structural optimization is mandatory in the design of aerospace structures. Design variables are repeatedly perturbed to satisfy non-linear constraints on displacements, stresses and critical buckling loads. Optimization methods can be divided in two main groups: Approximate Optimization Methods (AOM) and Global Optimization Methods (GOM). AOM formulate and solve a set of sub-problems where the original non-linear functions of the optimization problem are replaced by linear, quadratic or higher order approximations built including gradient information. Larger fractions of design space can be explored using multi-start approximate optimization (MSAO) where different optimization runs are performed starting from points generated randomly. The main difficulty of approximate optimization is to keep the quality of the approximation as highest as possible and always reliable in the region of design space currently being searched. Furthermore, approximate models should change during the optimization process based on the sequence in which design constraints become active. Global optimization methods search the optimum design by generating randomly a certain number of trial designs. This is done in purpose to expand the portion of design space explored by the optimizer thus increasing the probability of finding the global optimum

In preceding papers the authors have employed evanescent illumination to perform measurement of depth information on rough surfaces. In the developments presented in this paper new experimental evidence has been gathered. This information provides additional elements that help to formulate a more complete model of the phenomena taking place. The carried out measurements when confronted with independently gather information support the formulated model.

“Second generation” metaheuristic algorithms such as harmony search (HS) and big bang−big crunch (BB−BC) are very efficient in truss optimization problems but computationally expensive. This paper presents two hybrid formulations of HS and BB−BC where metaheuristic search is hybridized by including gradient/pseudo-gradient information as the criterion to accept or reject new trial designs or to perform new explosions. Each new trial design is formed by combining a set of descent directions and then eventually corrected to improve it further. An improved local 1D search derived from simulated annealing is also performed. The new algorithms are tested in two weight optimization problems of truss structures: (i) the classical planar 200-bar truss optimized with 29 design variables; (ii) a large-scale space-tower with 1938 elements and 204 design variables. Optimization results prove the efficiency and robustness of the optimization algorithms developed in the research described in this paper.

The bulge test is a versatile and reliable way to determine mechanical properties of thin films. It can be applied to obtain constitutive equations of the material at different ranges of deformation including time effects. It provides a biaxial state of stresses that is the prevailing condition in thin film operate. In this paper the bulge test information is retrieved with interferometric nano-moiré. A special set up was designed and built to pressurize a membrane in the platina of a conventional metrological microscope. The utilized field of view is 326 × 326 microns and the spatial resolution is 318 nanometers, the depth information is within 10 nanometers. An aluminum foil was cemented to a plate that has a circular aperture of 10 mm. The foil was inflated to 3.5 psi at 0.5 psi intervals and images were recorded at each pressure level. Local properties of the deformed surface were compared with the results of the membrane theory by determining from the experimentally measured values the surface trend. The comparison shows that the membrane takes the parabolic trend with maximum observed deviation of 43 nm. At the testing pressure of 3.5 psi the calculated radius of curvature from the surface trend is 96.8 mm, while the theoretical radius of curvature according to the geometry and material properties of aluminum foil is 96.3 mm.

Parylene-C is a bio-inert, bio-compatible and relatively inexpensive material with many bio-medical applications from coatings for implantable devices to bio-scaffolds. The main objective of this research was to demonstrate a novel approach to accurately measure the mechanical properties of free-standing fibrous thin-film substrates (TFS) of parylene-C. For that purpose, a two-stage experimental protocol based on the use of moiré contouring technology was developed. In this protocol, local measurements employing an advanced moiré setup that uses non-conventional illumination (i.e. evanescent field) are first performed to gather high-resolution information on a small region of the specimen; then, global measurements based on shadow moiré are performed to monitor the overall behavior of the membrane. The protocol was first calibrated for an aluminum foil and then partially applied to the fibrous parylene-C TFS. Material properties extracted from experiments are fully consistent with the data reported in literature and the results of a hybrid identification procedure based on the combination of finite element analysis and nonlinear optimization. The results will help lay the foundation for developing a comprehensive understanding of the influence that morphology and stresses play in the ability to enhance and sustain cell growth and tissue development, for biomedical applications.

This paper highlights the recently developed technique of Nano-Holographic Interferometry via far field microscopy. The main difference between conventional lens holography of phase objects and the methodology presented in this paper is that the observations are made well beyond the classical limits of optical resolution. Going beyond the resolution limits becomes feasible by the use of evanescent wave fronts as a source of illumination. The objects to be analyzed enter an excited state that produces pseudo-non-diffracting wave fronts. These wave fronts travel well beyond the traditional limits and enable the observations of nano-particles via a far field microscope. These discoveries open up new possibilities for Experimental Nano-mechanics that were previously thought impossible.

Numerous companies produce shape contouring devices based on the projection of an optical signal to obtain shape information. The basic principle for all of these devices is parallax determination. Parallax can be measured through projecting a small spot, a line, or a light pattern such as a grid. One application of this methodology is a gauge device in manufacturing processes where layers of materials are being deposited or removed to control the final geometry of the surface. The degree of accuracy achieved depends on the final required accuracy of the finished product. An essential aspect is measurement in real-time; real time stands for the time required by the controlling software to detect errors on the finished surface. The speed of the particular fabrication process dictates how quickly the software must be able to process information. The optical head must not reduce the speed of fabrication, and it should provide a warning of a faulty process fast enough to permit real-time corrections. In view of the real time requirement, the luminous signal processing must be reduced to a minimum. An optical head that projects a line is an excellent candidate for this operation because a line is the simplest form of the system that provides all of the required measurements in the case of the material deposition manufacturing process. This paper shows that a very high precision and accuracy are achievable in conjunction with extremely low processing times in a unique laser line projection setup. The unique aspect of this system is the ability to make these measurements regardless of surface conditions

In the study, described in this paper, the recently developed firefly algorithm (FFA) based meta-heuristic optimization method is utilized for the sizing of truss structures. The FFA solves optimization problems by mimicking the behaviour of fireflies. The efficiency of the FFA algorithm implemented in this study is tested on four classical weight minimization problems of truss structures. The optimization results are compared with those reported in the literature for other state-of-the-art meta-heuristic optimization methods. It is found that FFA can design lighter structures than other meta-heuristic methods and always converges to feasible designs

The Big Bang-Big Crunch (BB−BC) algorithm is a recently developed metaheuristic optimization method that mimics the process of evolution of the universe. The inherent simplicity of BB−BC is very attractive for structural optimization experts but the huge computational cost entailed by the optimization process is a serious obstacle to the large-scale diffusion of BB−BC. To overcome this problem, at least in the case of sizing optimization problems of truss structures, the paper presents an improved BB−BC formulation where each new trial design is always forced to lie on a descent direction. The efficiency of the new BB−BC algorithm is demonstrated by a trade study carried out on four classical weight minimization problems of truss structures that include various amounts of non-convexity in the design space

Il Big Bang–Big Crunch (BBBC) riproduce l'evoluzione dell'universo generando in maniera casuale una popolazione di design (fase di esplosione) e determinandone poi il centro di massa (fase di contrazione). Se il centro di massa migliore l’ottimo corrente si effettua nuova esplosione generando così una nuova popolazione per cui si valuta nuovamente il centro di massa. Tale processo si reitera fino a che non si arriva al design ottimo. Benché il BBBC sia uno degli algoritmi meta-euristici meglio formulati in assoluto, richiede un notevole sforzo computazionale. Per ovviare a tale limitazione, il presente lavoro propone una formulazione avanzata dell’algoritmo BBBC incorporando nel processo di generazione dei design candidati informazioni sui gradienti della funzione obiettivo. Il nuovo algoritmo è quindi un BBBC con esplosioni infrequenti. I risultati ottenuti in problemi di ottimizzazione di travature reticolari comprendenti sino a 3586 elementi e 280 variabili di sizing dimostrano la bontà dell'approccio proposto