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In this study, we conducted a theoretical analysis of thermal stress around an arbitrarily shaped hole in a thermoelectric material under electric current density and energy flux loading. Based on complex variable methods, conformal mapping, and analytical continuation theorem, the exact solutions of the thermal stress around a hole were obtained for the Seebeck coefficient and electric and heat conductivity. Based on the conversion efficiency equation of thermoelectric materials, higher electrical conductivity and lower heat conductivity should be selected to achieve an optimal design. The theoretical results indicated that higher electrical conductivity could reduce the thermal stress around the hole. However, energy flux and thermal stress concentration might be generated around the adiabatic hole due to the presence of a matrix with lower heat conductivity. Hence, thermoelectric materials with lower thermal conductivity should be selected carefully to avoid premature failure around the hole caused by thermal stress concentration. Finally, we also obtained and discussed the stress intensity factors of a hypocycloid-type crack.

Columnar-structured thermal barrier coating systems (TBCs) possess a strain tolerant columnar microstructure wherein the gaps between the columns are filled with high-porosity oxides. A numerical m...

Aims To determine whether half-threaded screw holes in a new titanium locking plate design can substantially decrease the notch effects of the threads and increase the plate fatigue life. Methods Three types (I to III) of titanium locking plates were fabricated to simulate plates used in the femur, tibia, and forearm. Two copies of each were fabricated using full- and half-threaded screw holes (called A and B, respectively). The mechanical strengths of the plates were evaluated according to the American Society for Testing and Materials (ASTM) F382-14, and the screw stability was assessed by measuring the screw removal torque and bending strength. Results The B plates had fatigue lives 11- to 16-times higher than those of the A plates. Before cyclic loading, the screw removal torques were all higher than the insertion torques. However, after cyclic loading, the removal torques were similar to or slightly lower than the insertion torques (0% to 17.3%), although those of the B plates were higher than those of the A plates for all except the type III plates (101%, 109.8%, and 93.8% for types I, II, and III, respectively). The bending strengths of the screws were not significantly different between the A and B plates for any of the types. Conclusion Removing half of the threads from the screw holes markedly increased the fatigue life of the locking plates while preserving the tightness of the screw heads and the bending strength of the locking screws. However, future work is necessary to determine the relationship between the notch sensitivity properties and titanium plate design. Cite this article: Bone Joint Res 2020;9(10):645–652.

This study investigated the effects of screw hole merging, thread removal, and screw hole offset on the mechanical properties of locking plates.Finite element models were used to develop the optimal design of the merged holes. Four titanium locking plates with different hole designs were analyzed. Type I had threaded round holes. Type II had merged holes. Type III had merged holes with partial thread removal. Type IV had threaded offset holes. Mechanical experiments similar to finite element analyses were conducted and compared. Screw bending tests were used to assess the screw holding power.Finite element analyses showed the optimal merging distance between two round screw holes was 3.5 mm with 2/3 circumferences in each hole. The stresses of types II and III were respectively 6.42% and 7.33%, lower than that of type I. The stress of type IV was 1.66% higher than that of type I. In the mechanical tests, the fatigue lives of types II and III were respectively 3.86 and 7.16 times higher than that of type I. The fatigue life of type IV was 37% lower than that of type I. The differences in the bending strengths of screws were insignificant.Merging holes could mitigate screw hole stress and increase the fatigue lives of the plates significantly. Partial thread removal could further improve the fatigue life. Merging holes and thread removal did not decrease the screw holding power significantly. The fatigue lives were significantly decreased in plates with offset holes.

Working length have been reported to affect the plate stress and fixation stiffness. However, the results of previous studies have been controversial. The present study was to determine working length effects on different locations of femoral bone gap.Five composite femurs with wide bone gaps at five levels (G1, 2, 3, 5, and 7), were fixed with locking plates. G1-3, G5 and G7 represented gaps at distal femur, distal-middle femur and middle femur respectively. Strain gauges were applied near the screw holes. The plate-bone constructs were loaded through a hemicylinder on the femoral head with total constraints at the distal femur. The micro-strains, axial stiffness and interfragmentary motions were recorded. Then the locking screws were removed one by one and the tests were re-run. The working length effects were compared and correlated.In distal femurs (G1-3), long working length was negatively correlated with the highest strains (r = -0.97, -0.95 and - 0.95, p 0.01) and axial stiffness (r = -1, -0.96 and -0.99, p 0.01). In distal-middle femurs (G5), as the working length increased, the highest strain decreased initially and then increased (r = 0.81, p = 0.026) and the axial stiffness decreased (r = -0.98, p 0.01). In middle femurs (G7), the highest strain and gap motions were much higher than that in the other groups and not significantly correlated with the working length change.Long working length could reduce the highest plate strain in distal femurs, but had no significant effects in middle femurs. The working length effects were markedly affected by the loading and boundary conditions.

An analytical solution to the antiplane elasticity problem associated with two circular inclusions interacting with a line crack is provided in this article. A series solution for the stress field ...

Background The fatigue fracture of locking plates can substantially threaten fracture treatment results. In the present study, three measures for modifying the screw hole structures of plates were implemented to improve their fatigue strength. Materials Custom-made identical titanium locking plates, except the screw hole configurations, were tested using four-point bending load. The three measures were partial removal of screw threads on the tension side of the plates, reduction of screw hole size, and modification of the thread radii. There were six types of plates: control (Type I), half of the threads removed (Type II) or one-third of the threads (Type III), smaller screw holes (Type IV), and increase of the thread root radii (Type V) or crest radii (Type VI). Findings Compared with the control, Types II and III significantly improved the fatigue strength (14.5 and 10.1 times, respectively). Decreasing the size of the screw hole (Type IV) also yielded a higher fatigue strength (17.6%). Type VI significantly improved the fatigue strength (9.8 times). However, Type V decreased the fatigue strength (14%). For cyclic stiffness, Type IV was significantly higher than other types statistically. Failure analyses showed typical fatigue fracture in all plates and the cracks were always initiated at the thread crest. Interpretations The fatigue strength of titanium locking plates can be significantly improved by structural changes in the screw holes. Removing the threads of the plates and increasing the crest radii of the threads were more effective measures than decreasing the size of the screw holes.

Introduction Reports of driver slippage leading to difficult locking screw removals have increased since the adoption of titanium for screw fabrication; the use of titanium is known to cause cross-threading and cold welding. Such problems occur most frequently in screws with hex sockets, and may cause serious surgical complications. This study aimed to improve screw socket design to prevent slippage and difficult screw removal. Materials and methods Three types of small sockets (hex, Torx, and cruciate) and six types of large sockets (hex, Torx, Octatorx, Torx+ I, Torx+ II, and Torx+ III) with screw head diameters of 5.5 mm were manufactured from titanium, and corresponding screwdrivers were manufactured from stainless steel. The screw heads and drivers were mounted on a material testing machine, and torsional tests were conducted to simulate screw usage in clinical settings at two insertion depths: 1 and 2 mm. Ten specimens were tested from each design, and the maximum torque and failure patterns were recorded and compared. Results For small sockets in 2 mm conditions, the hex with the largest driver core had the highest torque, followed by Torx and cruciate. In these tests, the drivers were twisted off in all specimens. However, under the 1 mm condition, the hex slipped and the torque decreased markedly. Overall, torque was higher for large sockets than for small sockets. The Octatorx, with a large core and simultaneous deformation of the driver and socket lobes, had the highest torque at almost twice that of the small hex. The hex had the lowest torque, a result of slippage in both the 1 and 2 mm conditions. Torx plus designs, with more designed degrees of freedom, were able to maintain a higher driving angle and larger core for higher torque. Conclusions The hex design showed slipping tendencies with a marked decrease in torque, especially under conditions with inadequate driver engagement. Large sockets allowed for substantial increases in torque. The Torx, Octatorx, and Torx plus designs displayed better performance than the hexes. Improvements to the socket design could effectively prevent slippage and solve difficult screw removal problems.

The failure behavior of thermal barrier coatings (TBCs) involves multilayered systems infiltrated with calcium–magnesium–alumino-silicates (CMAS). The metastable tetragonal phase is mainly composed of 7YSZ (7 mol.% Y2O3-stabilized ZrO2), and it destabilizes into the Y-lean tetragonal phase, which may be induced by CMAS infiltration, and transforms into a monoclinic phase during cooling. The phase transformation leads to volume expansion around the CMAS-rich layer. Furthermore, it is shown that the spalling of the coating system emerges when the surface of the coating system is subjected to significant residual stress. In this study, a double-cantilever beam model is established to describe the macroscopic phenomenon of thermal buckling induced via CMAS. The result of the buckle height is used to demonstrate the consistency of the experiment and finite element simulation. The experimental parameters are imported into a multilayer cantilever beam model to analyze the interfacial stresses due to CMAS infiltration. The finite element results indicate that the phase transformation leads to damage in the coating system wherein the interfacial stresses due to phase transformation are 27% higher than those in the model without phase transformation.

The problem of a circular elastic inclusion perfectly bonded to a matrix of infinite extent and subjected to arbitrarily thermal loading has been solved explicitly in terms of the corresponding homogeneous problem based on the inversion and Kelvin's transformation. It is to be noted that the relations established in this paper between the stress functions are algebraic and do not involve integration or solution of some other equations. Furthermore, the transformation leading from the solution for the homogeneous problem to that for the heterogeneous one is very simple, algebraic and universal in the sense of being independent of loading considered. The case of two bonded half-planes is obtained as a limiting case.

The interaction between a crack and two circular elastic inclusions for a fibrous tri-material composite under a remote uniform load is investigated. Based on the method of analytical continuation combined with the alternation technique, the solutions to the cracked composite are derived. A rapidly convergent series solution for the stress field, either in the matrix or the fibers, is obtained in an elegant form. The stress intensity factors are obtained numerically in terms of the dislocation density functions of the logarithmic singular integral equations. The merit of the present approach is the formulation of weakly singular integration that the integrals involved in the weakly singular allow easy calculations in the singular integral equation which can be treated to solve the problem even when a crack is closer to the interface. The stress intensity factors as a function of the dimensionless crack length for various material properties and geometric parameters are shown in graphic form. It is shown that the fibers act to restrain or accelerate crack growth depending on the shear moduli between the fibers and the matrix. With this understanding, an optimum design can thus be conceptualized for a fibrous composite system. The present proposed method can be further extended to deal with the corresponding crack problem associated with any number of inclusions.

Introduction Notch sensitivity may compromise titanium-alloy plate fatigue strength. However, no studies providing head-to-head comparisons of stainless-steel or titanium-alloy locking plates exist. Materials and methods Custom-designed identically structured locking plates were made from stainless steel (F138 and F1314) or titanium alloy. Three screw-hole designs were compared: threaded screw-holes with angle edges (type I); threaded screw-holes with chamfered edges (type II); and non-threaded screw-holes with chamfered edges (type III). The plates’ bending stiffness, bending strength, and fatigue life, were investigated. The stress concentration at the screw threads was assessed using finite element analyses (FEA). Results The titanium plates had higher bending strength than the F1314 and F138 plates (2.95:1.56:1) in static loading tests. For all metals, the type-III plate fatigue life was highest, followed by type-II and type-I. The type-III titanium plates had longer fatigue lives than their F138 counterparts, but the type-I and type-II titanium plates had significantly shorter fatigue lives. All F1314 plate types had longer fatigue lives than the type-III titanium plates. The FEA showed minimal stress difference (0.4%) between types II and III, but the stress for types II and III was lower (11.9% and 12.4%) than that for type I. Conclusions The screw threads did not cause stress concentration in the locking plates in FEA, but may have jeopardized the fatigue strength, especially in the notch-sensitive titanium plates. Improvement to the locking plate design is necessary.

In this study, the fracture origin is identified for the prismatic butt joints whose debonding condition can be expressed as a constant value of the ISSF. The ISSF variation is newly analyzed along the interface side by considering the real specimen geometry with chamfer at the corner. The detail fractographic observation shows that most of the fracture starts from the maximum ISSF region at the interface side instead of the interface corner. When the bondline thickness h is larger, the fracture origin can be seen at sub-surface because the stress triaxiality decreases inside of the specimen. The fracture origin under thermal loading can be estimated similarly because of the coincidence the ISSF variations.

In this paper, the problem of an elliptic hole embedded in an infinite plate interacting with an arbitrary point load is revisited by using the complex variable method. Based on analytical continuation theorem, the continuity conditions across the interface are automatically satisfied in a straightforward manner. It is shown that the solution for an infinite domain with an elliptic hole can be obtained from the solution of the corresponding homogeneous problem merely by a simple algebraic expression. This relation is universal in the sense of being independent of the loading considered. The solution of the corresponding homogeneous problem is considered as the principal part of the complex potentials while the complementary part of the complex potentials can be obtained by using analytical continuation theorem. Different expressions of the complementary part of the complex potentials are presented in this paper which are all proved to be the same result.

Pyroelectric harvesters convert time-dependent temperature variations into electric current. The appropriate geometry of the pyroelectric cells, coupled with the optimal period of temperature fluctuations, is key to driving the optimal load resistance, which enhances the performance of pyroelectric harvesters. The induced charge increases when the thickness of the pyroelectric cells decreases. Moreover, the induced charge is extremely reduced for the thinner pyroelectric cell when not used for the optimal period. The maximum harvested power is achieved when a 100 μm-thick PZT (Lead zirconate titanate) cell is used to drive the optimal load resistance of about 40 MΩ. Moreover, the harvested power is greatly reduced when the working resistance diverges even slightly from the optimal load resistance. The stored voltage generated from the 75 μm-thick PZT cell is less than that from the 400 μm-thick PZT cell for a period longer than 64 s. Although the thinner PZT cell is advantageous in that it enhances the efficiency of the pyroelectric harvester, the much thinner 75 μm-thick PZT cell and the divergence from the optimal period further diminish the performance of the pyroelectric cell. Therefore, the designers of pyroelectric harvesters need to consider the coupling effect between the geometry of the pyroelectric cells and the optimal period of temperature fluctuations to drive the optimal load resistance.

In this study, a mold for a micro-tip array is fabricated using a microlens array mask with proximity exposure. The micro-tip array uses a microlens array mask with geometrical optics. Light passing through a microlens is focused at the focal points. There is microlens on the mask and the pattern that results from the light passing through the mask is directly projected onto the photoresist surface. A concave profile is developed using a positive photoresist and the remaining photoresist microstructures are formed after the development process. By changing the distance between the mask and the photoresist and the radius of curvature of the microlens, various tip shapes can be fabricated. The exposure gap is calculated using the microlens array mask and the geometry of the mold of micro-tip array is established using the irradiance absorption maps for the different levels. These methods respectively use the model of the positive photoresist and optical software. When electroforming a metallic micro-tip copy of the patterned photoresist, masters are created. The metal micro-tip array is used membrane probe card.

This study presents a novel and precision process for fabricating a microneedle mold. The process includes a microlens array mask with contact printing in ultraviolet lithography. This method can precisely control the geometric profile of a microneedle array without the use of an etching process. The micro tapered cone microneedle mold utilizes the microlens array mask with geometrical optics. The light passes through the microlens and a hole in a Cr film of a mask, and then radiates onto the photoresist film. The light transmitted through the microlens has an aligned focal point on the photoresist film. An optical system is set up to characterize the optical performance of the machined microneedle, and then compared with theoretical data. The results show that the length of the microneedle from the experiment is close to the derived results. Moreover, the length of the microneedle is significantly influenced by the height and diameter of the microlens. Therefore, this method could also simplify the process and reduce the time needed for the fabrication of the microneedle. The micro cone microneedle has have great potential in the area of the drug delivery applications.

Pedicle screws are used for treating several types of spinal injuries. Although several commercial versions are presently available, they are mostly either fully cylindrical or fully conical. In this study, the bending strengths of seven types of commercial pedicle screws and a newly designed double dual core screw were evaluated by finite element analyses and biomechanical tests. All the screws had an outer diameter of 7 mm, and the biomechanical test consisted of a cantilever bending test in which a vertical point load was applied using a level arm of 45 mm. The boundary and loading conditions of the biomechanical tests were applied to the model used for the finite element analyses. The results showed that only the conical screws with fixed outer diameter and the new double dual core screw could withstand 1,000,000 cycles of a 50–500 N cyclic load. The new screw, however, exhibited lower stiffness than the conical screw, indicating that it could afford patients more flexible movements. Moreover, the new screw produced a level of stability comparable to that of the conical screw, and it was also significantly stronger than the other screws. The finite element analysis further revealed that the point of maximum tensile stress in the screw model was comparable to the point at which fracture occurred during the fatigue test.

This study presents a novel fabrication method for asymmetric microlens arrays for light control films that increase the efficiency of liquid crystal displays used to collect lateral light sources and improve the brightness within the angle of view. Initially, the pattern allows exposure through the placement of a photoresist-coated substrate on an inclined fixture. An inclined photoresist column array with a round cross section is constructed using a photolithography technique. During the incomplete thermal reflow processing, only the surface part of the photoresist column reaches the glass transition temperature (Tg) and is transformed from a glassy state into a rubbery state. In order to minimize the structural surface energy and reduce the surface area, the surface of the inclined photoresist column forms the shape of a lens. With proper control of the thermal reflow temperature and processing time, the photoresist at the base maintains its original inclination and glassy state, because it does not re...

A methodology was proposed to investigate the effect of hydride on the crack propagation in fuel cladding. The analysis was modeled based on an outside-in crack with radial hydrides located near its crack tip. The finite element method was used in the calculation; both stress intensity factor KI and J integral were applied to evaluate the crack stability. The parameters employed in the analysis included the location of radial hydride, hydride dimensions, number of hydrides, and the presence of circumferential hydride, etc. According to our study, the effective distance between a radial hydride and the assumed cladding surface crack for the enhancement of crack propagation proved to be no greater than 0.06 mm. For a hydride not on the crack line, it would induce a relatively minor effect on crack propagation if the vertical distance was beyond 0.05 mm. However, a longer hydride precipitate as well as double radial hydrides could have a remarkable effect on crack propagation. A combined effect of radial and circumferential hydrides was also discussed.

A new method for fabricating a novel dual-curvature microlens array with a high fill-factor using proximity printing in a lithography process is reported. The lens shapes include dual-curvature, which is a novel shape composed of triangles and hexagons. We utilized UV proximity printing by controlling a printing gap between the mask and substrate. The designed high density microlens array pattern can fabricate a dual-curvature microlens array with a high fill-factor in a photoresist material. It is due to the UV light diffraction which deflects away from the aperture edges and produces a certain exposure in the photoresist material outside the aperture edges. A dual-curvature microlens array with a height ratio of 0.48 can boost axial luminance up to 22%. Therefore, the novel dual-curvature microlens array offers an economical solution for increasing the luminance of organic light emitting diodes.

The problem of a layered structure containing an arbitrarily oriented crack crossing the interface in anti-plane elasticity is considered in this paper. The fundamental solution of displacements and stresses is obtained in a series form via the method of analytical continuation in conjunction with the alternating technique. A dislocation distribution along the prospective site of a crack is used to model a crack crossing the interface and the singular integral equations with logarithmic singular kernels for a line crack are then established. The crack is approximated by several line segments and the linear interpolation equation with undetermined coefficients was applied for the dislocation function along line segments. Once the undetermined dislocation coefficients are solved, the mode-III stress intensity factors KIII at two crack tips can be obtained for various crack inclinations with different material property combinations. All the numerical results are checked to achieve a good approximation that demonstrates the accuracy and the efficiency of the proposed method.

Anti-plane interaction of an elliptically cylindrical layered media with an arbitrarily oriented crack embedded in an infinite matrix, intermediate layer, or inner inclusion under a remote uniform shear load is considered in this paper. Based on the technique of conformal mapping and the method of analytical continuation in conjunction with the alternating technique, the solution for a screw dislocation in the inclusions and the matrix is first derived in a series form. The integral equations with logarithmic singular kernels for a line crack can easily be obtained by using the screw dislocation solutions as the Green's function together with the principle superposition. The stress intensity factors, which can properly reflect the interaction between a crack and an elliptically cylindrical layered media, are then obtained numerically in terms of the values of the dislocation density functions of the integral equations. The effects of material property combinations and geometric parameters on the normalized mode-III stress intensity factors are discussed in detail and shown in graphic form.

Short-segment instrumentation for spine fractures is threatened byrelatively highfailure rates. Failure of the spinal pedicle screws including breakage and loosening may jeopardize the fixation integrity and lead to treatment failure. Two important design objectives, bending strength and pullout strength, may conflict with each other and warrant a multiobjective optimization study. In the present study using the three-dimensional finite element (FE) analytical results based on an L25orthogonal array, bending and pullout objective functions were developed by an artificial neural network (ANN) algorithm, and the trade-off solutions known as Pareto optima were explored by a genetic algorithm (GA). The results showed that the knee solutions of the Pareto fronts with both high bending and pullout strength ranged from 92% to 94% of their maxima, respectively. In mechanical validation, the results of mathematical analyses were closely related to those of experimental tests with a correlation coefficient of −0.91 for bending and 0.93 for pullout (P<0.01for both). The optimal design had significantly higher fatigue life (P<0.01) and comparable pullout strength as compared with commercial screws. Multiobjective optimization study of spinal pedicle screws using the hybrid of ANN and GA could achieve an ideal with high bending and pullout performances simultaneously.

Anterior Lumbar Interbody Fusion (ALIF) has been widely used to treat internal disc degeneration. However, different cage positions and their orientations may affect the initial stability leading to different fusion results. The purpose of the present study is to investigate the optimum cage position and orientation for aiding an ALIF having a transfacet pedicle screw fixation (TFPS). A three-dimensional finite element model (ALIF with TFPS) has been developed to simulate the stability of the L4/L5 fusion segment under five different loading conditions. The Taguchi method was used to evaluate the optimized placement of the cages. Three control factors and two noise factors were included in the parameter design. The control factors included the anterior-posterior position, the medio-lateral position, and the convergent-divergent angle between the two cages. The compressive preload and the strengths of the cancellous bone were set as noise factors. From the results of the FEA and the Taguchi method, we suggest that the optimal cage positioning has a wide anterior placement, and a diverging angle between the two cages. The results show that the optimum cage position simultaneously contributes to a stronger support of the anterior column and lowers the risk of TFPS loosening.

Using radio-frequency magnetron sputtering, various interlayer materials (Cu, Al, Ag, and ZnO) were added to indium-tin oxide (ITO) films on a polyethylene terephthalate (PET) flexible substrate, and were compared to examples made without an interlayer. The effects of the interlayer on the ITO were investigated with X-ray diffractometry (XRD), visible wavelength photospectrometry, four-point probe electrical resistivity, and micro-scratch adhesion tests, which were all conducted at four temperatures (25°C, 35°C, 55°C, and 75°C). The ITO crystallographic texture was overwhelmingly found to be (2 2 2), for all combinations considered. The grain size was reduced in the ITO films having interlayers of Ag or Cu, and was enlarged by the ZnO. The visible light transmittance remained almost unchanged for the Al and ZnO buffers, but Ag and Cu failed to maintain the industry standard of 75–80% for a transparent film. Cu, ZnO, and especially Ag, effectively reduced, whereas, Al increased the sheet resistance of the ...

This paper presents an analytical solution for plane elasticity problems of an elliptically cylindrical layered media subject to an arbitrary edge dislocation. Based on the technique of conformal mapping and the method of analytical continuation in conjunction with the alternating technique, the general expressions of the displacements and stresses, where an edge dislocation is located in matrix, coating layer and inclusion are obtained. The numerical results of image forces exerted on a generalized edge dislocation are carried out by using the generalized Peach–Koehler equation. As a numerical illustration, both the image forces and equilibrium positions are presented for different material combinations and relative thickness of a coating layer. The result shows that the thickness and the shear modulus of the coating layer have a strong influence on the stability of dislocation.

A new method to fabricate a high fill-factor dual-curvature microlens array using the proximity printing in lithography process is reported. The technology utilized the UV proximity printing by controlling a printing gap between the mask and substrate. The designed high density microlens array pattern can produce high fill-factor dual-curvature microlens array in photoresist. It is due to the UV light diffraction to deflect away from the aperture edges and produce a certain exposure in photoresist material outside the aperture edges. This method can precisely control the geometric profile of high fill factor dual-curvature microlens array. The experimental results showed that the dual-curvature micro-lens array in photoresist could be formed automatically when the printing gap ranged from 360 to 600 µm. The gapless dual-curvature microlens array will be used to enhance of luminance and uniformity for light-emitting diodes.

This paper is concerned with direct energy conversion of waste heat into electrical energy by performing the Olsen cycle on lead nickel niobate zirconate titanate (PNNZT) pyroelectric ceramics undergoing a relaxor-ferroelectric phase transition. First, isothermal bipolar displacement vs. electric field hysteresis loops were measured for different temperatures and electric field spans. The Curie temperature varied between 150 °C and 240 °C as the electric field increased from zero up to 3 MV/m. The energy and power densities of the Olsen cycle on PNNZT were measured by cycling the specimens over a wide range of temperatures, electric fields, and frequencies. A maximum energy density of 1417 J/L/cycle was recorded with 200 μm thick PNNZT cycled at 0.033 Hz between temperatures 20 °C and 240 °C and electric fields 0.3 MV/m and 9.0 MV/m. To the best of our knowledge, this is the largest energy density ever obtained experimentally for any pyroelectric material. In addition, a maximum power density of 78 W/L was measured by cycling the material temperature between 20 °C and 220 °C and applying the electric field between 0.3 MV/m and 9.0 MV/m at 0.09 Hz.

A titanium mesh cage (TMC) might develop subsidence and cause local kyphotic deformity of the spine. For prevention of this complication, this study was designed to find the most appropriate spike design for a vertebral body cage (VBC). In order to investigate the subsidence of a VBC, three‐dimensional finite element models of the L5 spinal model with a nonlinear contact analysis have been developed. Then, the Taguchi robust design method was used to evaluate spike designs. Finally, the mechanical experiment was developed to obtain the compressive strength of the VBC. For the results of the FEM‐based Taguchi method, the spike row, the spike obliquity, and the spike height were especially important factors for preventing the subsidence. The optimum combinations were pyramidal spike type, a spike height of 2 mm, a spike diameter of 1.4 mm, an oblique geometry, 11 rows per 28 mm, and an inner diameter of 10 mm. For the results of the experiment, the good relationship between finite element simulatio...

A theoretical approach for an optical lens tip on a single-mode fiber end to improve power coupling from laser diode is presented in this work. The lens shape considered here is an ellipsoid. Based on scalar diffraction and Gaussian mode shapes for the laser and fiber fields, a theoretical model is developed to predict the coupling performance of this microlens. Theoretically, both a high coupling efficiency up to 77% and a large alignment tolerance for 10% off-peak are achieved. The proposed method facilitates mass production to achieve a high-yield and high-coupling efficiency that is suitable to be used in the commercial fiber transmission industry.

Joint distraction and mobilization with a hinged external fixator preserves elbow stability and mobility. However, the alignment of both elbow and fixator hinges was the initial prerequisite of the arthrodiatasis technique. The main goal of this study was to numerically evaluate the kinematic influence of the device, surgery, and joint factors on hinge alignment. The kinetic effects of the pins placement and elbow angle on concentric distraction and mobilization were also discussed. A unilaterally hinged elbow-fixator system with a 14 links and 10 degrees-of-freedom was instrumented into a humeroulnar model. The Denavit-Hartenberg method with the homogeneous transformation matrixes was applied to perform kinematic analysis of the linkage system. The predicted results revealed that the concurrence of hinge alignment (i.e., kinematic) and concentric distraction (i.e., kinetic) necessitates two telescopic tubes orthogonal to the elbow hinge. The degrees-of-freedom arrangement of the fixator articulators plays a significant role in hinge alignment. After joint distraction, two hinges might be misaligned due to the difference in the structural rigidity of the pins, fixator, and stiffened elbow. Furthermore, those two prerequisite are interactive and sensitive to elbow angle, fixator design, and pin placement of the bridged elbow-pin-fixator construct. In addition, the ideally concentric distraction might occur only at an elbow angle of 120 degrees owing to the ulnar anatomy. Meticulous planning is necessary for such highly technically demanding surgery.

This paper presents a novel and precision process to fabricate an array of micro metal vertical probes with various tip angles. The process includes an inclined and multiple ultraviolet (UV) lithography, contact lithography and Ni electroforming technology. The tips of micro pyramid vertical probe array utilize the inclined and multiple exposures cooperated with Snell's law. Due to the light pass through an optical transparent homogenous material, the material refractive index results in light path deflection. By changing the workpiece inclination, controllable various tip angles can be fabricated. The experimental results showed that micro metal vertical probes with 54°, 60° and 68° tip angles. The micro-pyramidal vertical probe array can be used in vertical-type probe cards without the conventional complicated assembly.

A simple and effective method to fabricate a high fill-factor triangular microlens array using the proximity printing in lithography process is reported. The technology utilizes the UV proximity printing by controlling a printing gap between the mask and substrate. The designed approximate triangle microlens array pattern can be fabricated the high fill-factor triangular microlens array in photoresist. It is due to the UV light diffraction to deflect away from the aperture edges and produce a certain exposure in photoresist material outside the aperture edges. This method can precisely control the geometric profile of high fill factor triangular microlens array. The experimental results showed that the triangular micro-lens array in photoresist could be formed automatically when the printing gap ranged from 240 mum to 840 mum. The gapless triangular microlens array will be used to increases of luminance for backlight module of liquid crystal displays.

This paper demonstrates the effective coupling between a single-mode fiber (SMF) and an edge emitting laser diode (LD) using a semi-ellipsoid microlens on the SMF endface. The semi-ellipsoid microlens was fabricated using photolithography, thermal reflow, mold electroforming and polydimethylsiloxane (PDMS) injection. UV-curing glue was smeared and exposed to fasten the lens onto the fiber. This microlens allows increasing the fiber spot size and numerical aperture. Low loss, wide misalignment tolerance and low manufacturing cost could be achieved. The optical simulation-software “TracePro” was used to predict the coupling efficiency parameters for the LD to SMF. “Taguchi method” was used for the parameter design concept to improve product quality searching for the optimal lens design. The proposed method facilitates mass production to achieve a high-yield and high-coupling method that is suitable to be used in the commercial fiber transmission industry.

Study Design: Comparative in vitro biomechanical study and finite element analysis. Objectives: To investigate the bending strength and pullout strength of conical pedicle screws, as compared with conventional cylindrical screws. Summary of Background Data: Transpedicle screw fixation, the gold standard of spinal fixation, is threatened by screw failure. Conical screws can resist screw breakage and loosening. However, biomechanical studies of bending strength have been lacking, and the results of pullout studies have varied widely. Methods: Ten types of pedicle screws with different patterns of core tapering and core diameter were specially manufactured with good control of all other design factors. The stiffness, yielding strength, and fatigue life of the pedicle screws were assessed by cantilever bending tests using high-molecular-weight polyethylene. The pullout strength was assessed by pullout tests using polyurethane foam. Concurrently, 3-dimensional finite element models simulating these mechanical tests were created, and the results were correlated to those of the mechanical tests. Results: In bending tests, conical screws had substantially higher stiffness, yielding strength, and fatigue life than cylindrical screws (P

This paper presents a novel method for fabricating the horizontal frustum structure as a planar optical waveguide using the proximity printing technique. A horizontal frustum optical waveguide with both lateral and vertical taper structure was produced. The orthogonal and inclined masks with the diffraction effect were employed in the lithography process. This method can precisely control each horizontal frustum optical waveguide geometric profile in the fabrication process. The horizontal frustum optical waveguide and its array with the same inclined angle were generated. The beam propagation simulation software (BPM_CAD) was used to model the optical performance. The simulation results reveal that the mode profile matched into horizontal frustum optical waveguide and fiber from the laser diode. The optical loss of the horizontal hemi-frustum optical waveguide structure was less than 0.2 dB. The horizontal hemi-frustum waveguide will be used for fiber coupling on boards for future optical communication systems.

A procedure for fabricating a periodic structure on a metal at submicron order using holographic interferometry and molding processes is described. First, holographic interference using a He-Cd (325nm) laser is used to create the master of the periodic line structure on an i-line sub-micron positive photoresist film. A 200nm nickel thin film is then sputtered onto the positive photoresist. Pattern is then transferred to a metal using Nickel-Cobalt electroforming. Initial results show the technique can accurately control the grating’s period and depth.

The quality control of integrated circuit (IC) processing is becoming more and more important as the wafer becomes larger and the feature size shrinks. However, an advanced IC fabrication process consists of 300+ steps with scarce and usually difficult quality measurements. Thus product yield may not be realized until months into production while in-line measurements are available on the order of a millisecond. The series production nature and measurement setup lead to a unique process control problem. In this work, typical disturbances are explained and the possibility for inferential control is explored. This leads to a control architecture with multiple layers in a cascade structure. Next, the rapid thermal processing (RTP) is used to illustrate recipe generation and control structure design at the tool level. The resultant multivariable controller gives satisfactory setpoint tracking for a triangular-like temperature program. Effective delay in a feedback loop at the process level is also clarified which can be used to design a run-to-run controller or to prioritize the measurement queue for the metrology tool. In order to prolong the time between maintenance and to reduce rework, process trend monitoring of a tool is essential. Instead of using entire batch data, a key process variable is identified and an index is computed to capture dynamic behavior of the tool. An IC processing example is used to illustrate this approach and results clearly indicate that process trend is well predicted using the index-based time-series model. Finally, future research directions for improved semiconductor manufacturing are also described.