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This study developed an in-mold induction heating system for the injection compression molding process to overcome the problem of incomplete filling of microstructures caused by the formation of skin layers and residual stress caused by flow. Moldex3D software was used with the Taguchi method to optimize the molding parameters for both injection molding and injection compression molding, with the aim of reducing warpage and improving optical quality. The in-mold induction heating system has extremely high heating efficiency. Experiments revealed that a time of only 8 s was required to inducted-heat up the core to the glass transition temperature which keeps the melt under a good state of flow and allows a replication rate of 97%. In addition, the ICM process can effectively reduce the flow-induced residual stress and improve the optical properties of the obtained samples. Finally, the illuminance of the product fabricated through ICM with induction heating for 10 s was 2.3 times higher than that of the product obtained through ICM without induction heating. Accordingly, the proposed induction heating system is feasible for use in ICM the rapid manufacturing of high-quality optical products with microstructures. KEYWORDS induction heating, injection compression molding, microstructure, optical property, residual stress, Taguchi method, 1 | INTRODUCTION Injection molding (IM) has been extensively used to fabricate various high-precision products. Conventional IM techniques have been used for the mass production and the fabrication of products [...]

Relatively recently, we advanced a route to create, in a controlled fashion, combined horizontal and vertical stratified structures by simple and energyefficient processing operations employing static mixing elements. While in state-of-the-art static mixing the focus is on layer multiplication, here the aim is to create hierarchical fractal structures. Therefore, the main question addressed in this article is how structures, rather than layers, can be multiplied. The key aspect is the addition of layers on the sides or in the midplane of the flow during the process; every addition step increases the hierarchy by one level. This article derives the general formalism for forming fractal structures with controlled hierarchy, and we develop the language required to design and construct the dies. The main part of the article addresses this main topic and is based on the splitting serpentine static mixer geometry that can be easily made on the parting surfaces of a mold on both the micro- and the macroscale. The second part of the article addresses the strategy to minimize the number of mirroring steps, eventually avoiding mirroring completely, and is based on the rotation-free multiflux static mixer geometry. With the design language derived, complex hierarchical fractal structures can be generated simply by changing the number and sequence of operators within extrusion dies or molds, providing a one-step solution to produce material structures for potential use in diverse applications ranging from advanced mechanical systems to photovoltaic devices, where controlled assembly of dissimilar materials, and the realization of huge interfaces and genuine cocontinuity throughout the cross section, is critical. KEYWORDS microlayers, microstructures, processing, static mixers, 1 | INTRODUCTION The last two decennia witnessed major efforts in the design of different routes to structure organic matter, such as polymers, down to the nanoscopic level for use [...]

The phase field method has been shown to have tremendous potential to serve as a continuum modeling approach of microstructural evolution mechanisms in many contexts, such as alloy solidification, fracture, [...]

Over the past few years, metal additive manufacturing (AM) technologies including laser powder bed fusion (LPBF) have benefited from high interest in both research and industry [1,2]. LPBF relies on [...]

The slow crack growth (SCG) in high density polyethylene (HDPE) is a phenomenon dominated by crazing. In this work, the crazing was analyzed from a microstructural point of view. PENT (Pennsylvania Edge Notched Tensile) test was chosen to study the evolution of the craze with time for different resins from PE-80 up to PE-100 grades. Two different geometries, the standard and an alternative named CDNT (Circumferentially Deep Notched Tensile), were employed. Failure times were correlated with intercrystalline parameters like tie molecules and the molecular weight between entanglements. Experimental results showed good correlations using both direct SCG test (standard PENT and CDNT geometries). Finally, the strain hardening modulus was correlated with PENT failure times. The results disclosed an outstanding correlation for several polyethylene grades from blow molding up to PE-80, PE-100, and higher resistant to crack grades. These results permitted an easy-classifying and ranking method as much to the old polyethylene grades as to the new generation of HDPE resins with a very high SCG resistance., INTRODUCTION Slow crack growth (SCG) is the most common long-term failure process in polyethylene (PE) pipes [1]. SCG phenomenon has been extensively studied to establish some of the features that [...]

The geotechnical behaviour of very weak pyroclastic rocks controls both the failure mechanisms at the margins of rock mesas, where historic hill towns are often sited, as well as the stability of old underground cavities in urban areas of Central Italy. The study focuses on the mechanical behaviour of one of the pyroclastic materials forming the Orvieto mesa (pozzolana), not unlike other pozzolanas in Central and Southern Italy and other pyroclastites from volcanic districts worldwide. The mechanical properties under static conditions of this weakly cemented rock are reported. A petrographic and physical characterization of the material was preliminary conducted, followed by a wide range of mechanical tests: oedometer, uniaxial, and isotropic compression tests and indirect tensile tests. The stress-strain and strength behaviours of the pozzolana are highlighted and compared with those of the rock materials of the pyroclastic formation (tuff). The mechanical behaviour of the pozzolana is related to its physical and textural characters, with special reference to continuity of the groundmass and porosity. Finally, the role of the material behaviour at the field scale is discussed. Key words: pyroclastic flow, volcanic rock, compressibility, elastic wave velocity, laboratory tests. Le comportement geotechnique de roches pyroclastiques tres faibles controle autant les mecanismes de rupture sur les marges des mesas rocheuses, ou les villages historiques sont souvent places, que la stabilite des anciennes cavites souterraines, dans les zones urbaines au centre de l'ltalie. L'etude s'interesse au comportement mecanique d'un des materiaux pyroclastiques (pouzzolane) qui forment la mesa sur la quel la ville d'Orvieto a ete construite, semblable a d'autres pouzzolanes dans le centre et le sud de l'ltalie et a d'autres pyroclastites provenant de districts volcaniques ailleurs dans le monde. L'article presente les proprietes mecaniques en conditions statiques de ce type de roche faiblement cimentee. Une caracterisation preliminaire petrographique et physique du materiau a ete realisee, suivie d'une vaste gamme d'essais mecaniques: essais redometriques, essais en compression uniaxiale et isotrope, et essais de traction indirecte. Les comportements en contraintedeformation et en resistance de la pouzzolane sont presentes et compares a ceux de la couche lithique de la formation pyroclastique (tuf). Le comportement mecanique de la pouzzolane est relie a ses proprietes physiques et texturales, avec une reference particuliere a la continuite de la mesostase et a la porosite. Enfin, le role du comportement du materiau a l'echelle de terrain est discute. [Traduit par la Redaction] Mots-cles: ecoulement pyroclastique, roche volcanique, compressibilite, vitesse des ondes elastiques, essais en laboratoire., Introduction Since antiquity, small towns in the volcanic areas of Central and Southern Italy have been built on deposits that originated from pyroclastic flows. The geotechnical properties of these materials [...]

This study proposes an analytical model to relate the evolving microstructure of neat cement paste during hydration to the electrical resistivity measurement. The model is based on the general effective media theory and considers the contributions of both the low-resistivity phase (capillary pores) and the high-resistivity phase (gels and solids) in cement-pastes. The major parameters in the proposed model are the microstructural properties such as capillary pore percolation threshold and pore structure parameter, capillary pore phase and solid-gel phase resistivities. To validate the model, an empirical relationship between the resistivity formation factors and the phase volume fractions of a series of cement pastes has been built up with the assistance of noncontact electrical resistivity measurement and mercury intrusion porosimetry technique. The good agreement between the model and experimental data shows that it is feasible to obtain better understandings of the evolving microstructure of cement paste during the hydration using electrical resistivity measurement. Furthermore, based on the log-linear increase of resistivity with time, the porosity up to an age of a few months can be predicted by the proposed model. The predicted results show a good correlation with the experimental results in previous studies. DOI: 10.1061/(ASCE)0899-1561(2009)21:11(648) CE Database subject headings: Microstructures: Cement; Porosity; Electrical resistivity.

Microlevel material failure has been recognized as one of the main modes of failure for rolling contact fatigue (RCF) of bearing. Therefore, microlevel features of materials will be of significant importance to RCF investigation. At the microlevel, materials consist of randomly shaped and sized grains, which cannot be properly analyzed using the classical and commercially available finite element method. Hence, in this investigation, a Voronoi finite element method (VFEM) was developed to simulate the microstructure of bearing materials. The VFEM was then used to investigate the effects of microstructure randomness on rolling contact fatigue. Here two different types of randomness are considered: (i) randomness in the microstructure due to random shapes and sizes of the material grains, and (ii) the randomness in the material properties considering a normally (Gaussian) distributed elastic modulus. In this investigation, in order to determine the fatigue life, the model proposed by Raje et al. ('A Numerical Model for Life Scatter in Rolling Element Bearings,' ASME J. Tribol., 130, pp. 011011-1-011011-10), which is based on the Lundberg-Palmgren theory ('Dynamic Capacity of Rolling Bearings,' Acta Polytech. Scand., Mech. Eng. Ser., 1(3), pp. 7-53), is used. This model relates fatigue life to a critical stress quantity and its corresponding depth, but instead of explicitly assuming a Weibull distribution of fatigue lives, the life distribution is obtained as an outcome of numerical simulations. We consider the maximum range of orthogonal shear stress and the maximum shear stress as the critical stress quantities. Forty domains are considered to study the effects of microstructure on the fatigue life of bearings. It is observed that the Weibull slope calculated for the obtained fatigue lives is in good agreement with previous experimental studies and analytical results. Introduction of inhomogeneous elastic modulus and initial flaws within the material domain increases the average critical stresses and decreases the Weibull slope. [DOI: 10.1115/1.3063818] Keywords: Voronoi finite element method, material microstructure, numerical simulation, rolling contact fatigue, bearing life, contact stresses

We present computationally efficient models and approaches to simulate the response of microstructures under mechanical shock. These approaches include a Galerkin-based reduced-order model and a hybrid approach utilizing the response of structures to static loads combined with the dynamic shock spectrum of a spring-mass-damper system. To demonstrate the accuracy and efficiency of these approaches, we apply them on cantilever and clamped-clamped microbeams, and compare their predictions with analytical and finite-element (FE) results. We conclude that the hybrid approach is computationally efficient and accurate for microstructures behaving linearly in both quasi-static and dynamic loading conditions. The hybrid approach enables using simple analytical expressions that can be easily utilized by microelectromechanical system designers to judge the reliability of their devices. We show that reduced-order models are capable of capturing accurately the dynamic behavior of microstructures under shock pulses of various amplitudes (low-g and high-g), damping conditions, structural boundaries, and can capture linear and nonlinear behavior. Our results indicate that modeling the shock force as a quasi-static force for microstructures with low-natural frequencies may lead to erroneous results. High-g loading cases are investigated. Significant increase in the computational cost of simulations is reported when using traditional FE models because of the activation of higher order modes. The developed reduced-order model employing at least six modes is shown to be efficient in such cases. Design parameters are investigated to determine their effect on the shock resistance of microstructures. It is concluded that increasing air damping and tensile residual stresses improves the shock resistance of microstructures. A case study for the response of an optical fiber switch to shock is presented. [2006-0131] Index Terms--Clamped, high-g shock, microbeams, microelectromechanical system (MEMS) reliability, nonlinearity, reduced-order models, shock spectrum.

A microstructure-level model for simulation of machining of cast irons using the finite element method is presented. The model explicitly combines ferritic and pearlitic grains with graphite nodules to produce the ductile iron structure. The behaviors of pearlite, ferrite, and graphite are captured individually using an internal state variable model for the material model The behavior of each phase is dependent on strain, strain rate, temperature, and amount of damage. Extensive experimentation was conducted to characterize material strain rate and temperature dependency of both ferrite and pearlite. The model is applied to orthogonal machining of ductile iron. The simulation results demonstrate the feasibility of successfully capturing the influence of microstructure on machinability and part performance. The stress, strain, temperature, and damage results obtained from the model are found to correlate well with experimental results found in the literature. Furthermore, the model is capable of handling various microstructures in other heterogeneous materials such as steels. [DOI: 10.1115/1.1455642]

In this paper, a microgranular mechanics approach is used to derive an expression for the elastic moduli of an assembly of bonded granulates, based on the response of two particles that are connected by an elastic binder. The derived modulus is a function of the particle/binder modulus, the particle size, the binder thickness, the binder width, the assembly coordination number, the binder content, and the porosity. To demonstrate its applicability, the predicted range of the modulus using the derived model is compared with that measured from experiments. The difference between this method and the traditional homogenization models will be discussed.

This work presents a new strain sensor with a compact structure. The strain sensor comprises of a pair of cantilever beams with different lengths connected by a short tip. The residual strain causes two beams to deflect each other, thereby magnifying the deflection, which is measured by the tip. The displacement is independent of both Young's modulus and the film's thickness. An analytical model is derived to relate the measured displacement to residual strain. Finite-element modeling is also used to analyze the model. This work also thoroughly considers other factors that influence the designs and the implicit limitations of the strain sensors. Experimental results with an Si[O.sub.2] film as well as undoped LPCVD polysilicon films are used to demonstrate the effectiveness of the proposed structure. Index Terms - Residual strain, thin film.

The use of the one-dimensional phase field method based on the adaptive grid technique for modeling the mechanics of solidification. Three problems were considered for this purpose, namely, the classical Stefan model, a modified Stefan model with a generalized kinetic undercooling term and the case of a solid sphere in equilibrium with its melt. Experimental results showed that adaptive grid techniques present computational advantages, allowing speed-ups of the order of hundreds of times to be obtained for comparable accuracy.

A sticking (stiction) model for a cantilevered beam is derived. This model includes the effect of the bending moment, which stems from stress gradient along the vertical direction of structural polysilicon, and the temperature during the release process. The bending moment due to the stress gradient will play an important role to evaluate antisticking efficiency since liquid tension and surface energy of microstructures tend to become smaller by newly developed antisticking techniques. The effects of stress gradient and temperature were analyzed and verified with surface-micromachined polysilicon cantilevers. By modifying the substrate polysilicon with grain-hole formation technique, the effects of residual stress gradient in polysilicon on stiction could be observed in the condition of low work of adhesion. Index Terms - Grain hole, polysilicon, sticking, stress gradient, surface micromachining.

A probabilistic model allows the study of the effect of microstructural changes on fatigue crack growth of large cracks in structural alloys. The model employs a microstructure-based fatigue crack growth law. The law relates the growth rate, dislocation barrier spacing, yield stress, fatigue ductility coefficient, Young's modulus and the dislocation cell size. The application of the model to steels and Ti-alloys are discussed.

Negative poisson's ratio is exhibited by a newly developed composite material. This material has a reentrant microstructure and isotropic due to arbitrary distribution of the microstructure. This negative poisson ratio enables the material to expand laterally when subjected stress and strain. This new material exists within the classical framework of elasticity.

An analysis of the growth and control of the microstructure and properties within a computer-aided design/computer-aided manufacturing (CAD/CAM) system is given. A mathematical model is used to forecast the microstructure and properties from the material processing used and the material composition. The material studied is a specially hardened Al-Li-Zr alloy from the Aluminum Company of America. The particle size, distribution, the free zone width, the critical resolved shear strength and yield strength were all computed by using the model.

A two-dimensional model for the coercivity mechanism of [Sm.sub.2][(Co, Fe, Cu, Zr).sub.17] magnets is proposed. The high coercivities of fully heat-treated magnets (> 20 kA/cm) result from pinning sites which are formed by the intersections of the Zr-rich platelet phase (Z-phase) and the Cu-rich Sm[Co.sub.5] (1/5) boundary phase. The pinning strength of this site is assumed to be a result of the large difference between the domain wall energies of the 1/5 phase and the Z-phase. The domain wall energies of almost single phase samples of the Z-phase have been determined by magnetic measurements and by quantitative analysis of domain patterns. The small domain wall energy of the Z-phase of 4 - 11 mJ/[m.sup.2] supports the presented model.

A computational simulation method for three-dimensional trabecular surface remodeling was proposed, using voxel finite element models of cancellous bone, and was applied to the experimental data. In the simulation, the trabecular microstructure was modeled based on digital images, and its morphological changes due to surface movement at the trabecular level were directly expressed by removing/adding the voxel elements from/to the trabecular surface. A remodeling simulation at the single trabecular level under uniaxial compressive loading demonstrated smooth morphological changes even though the trabeculae were modeled with discrete voxel elements. Moreover, the trabecular axis rotated toward the loading direction with increasing stiffness, simulating functional adaptation to the applied load. In the remodeling simulation at the trabecular structural level, a cancellous bone cube was modeled using a digital image obtained by microcomputed tomography ([micro]CT), and was uniaxially compressed. As a result, the apparent stiffness against the applied load increased by remodeling, in which the trabeculae reoriented to the loading direction. In addition, changes in the structural indices of the trabecular architecture coincided qualitatively with previously published experimental observations. Through these studies, it was demonstrated that the newly proposed voxel simulation technique enables us to simulate the trabecular surface remodeling and to compare the results obtained using this technique with the in vivo experimental data in the investigation of the adaptive bone remodeling phenomenon. [DOI: 10.1115/1.1392315]

A microstructural model of cartilage was developed to investigate the relative contribution of tissue matrix components to its elastostatic properties. Cartilage was depicted as a tensed collagen lattice pressurized by the Donnan osmotic swelling pressure of proteoglycans. As a first step in modeling the collagen lattice, two-dimensional networks of tensed, elastic, interconnected cables were studied as conceptual models. The models were subjected to the boundary conditions of confined compression and stress-strain curves and elastic moduli were obtained as a function of a two-dimensional equivalent of swelling pressure. Model predictions were compared to equilibrium confined compression moduli of calf cartilage obtained at different bath concentrations ranging from 0.01 to 0.50 M NaCl. It was found that a triangular cable network provided the most consistent correspondence to the experimental data. The model showed that the cartilage collagen network remained tensed under large confined compression strains and could therefore support shear stress. The model also predicted that the elastic moduli increased with increasing swelling pressure in a manner qualitatively similar to experimental observations. Although the model did not preclude potential contributions of other tissue components and mechanisms, the consistency of model predictions with experimental observations suggests that the cartilage collagen network, prestressed by proteoglycan swelling pressure, plays an important role in supporting compression. [S0148-0731(00)00704-4]