Combined Effect Of Thickness Research Articles

Impact of ZrO2 nanoparticles addition on flexural properties of denture base resin with different thickness.

PURPOSEThis study aimed to evaluate the effect of incorporating zirconium oxide nanoparticles (nano-ZrO2) in polymethylmethacrylate (PMMA) denture base resin on flexural properties at different material thicknesses.MATERIALS AND METHODSHeat polymerized acrylic resin specimens (N = 120) were fabricated and divided into 4 groups according to denture base thickness (2.5 mm, 2.0 mm, 1.5 mm, 1.0 mm). Each group was subdivided into 3 subgroups (n = 10) according to nano-ZrO2 concentration (0%, 2.5%, and 5%). Flexural strength and elastic modulus were evaluated using a three-point bending test. One-way ANOVA, Tukey's post hoc, and two-way ANOVA were used for data analysis (α = .05). Scanning electron microscopy (SEM) was used for fracture surface analysis and nanoparticles distributions.RESULTSGroups with 0% nano-ZrO2 showed no significant difference in the flexural strength as thickness decreased (P = .153). The addition of nano-zirconia significantly increased the flexural strength (P < .001). The highest value was with 5% nano-ZrO2 and 2 mm-thickness (125.4 ± 18.3 MPa), followed by 5% nano-ZrO2 and 1.5 mm-thickness (110.3 ± 8.5 MPa). Moreover, the effect of various concentration levels on elastic modulus was statistically significant for 2 mm thickness (P = .001), but the combined effect of thickness and concentration on elastic modulus was insignificant (P = .10).CONCLUSIONReinforcement of denture base material with nano-ZrO2 significantly increased flexural strength and modulus of elasticity. Reducing material thickness did not decrease flexural strength when nano-ZrO2 was incorporated. In clinical practice, when low thickness of denture base material is indicated, PMMA/nano-ZrO2 could be used with minimum acceptable thickness of 1.5 mm.

Prediction of Broadband Noise from Symmetric and Cambered Airfoils

Aerodynamic sound generation and self-noise mechanisms from lifting surfaces such as airfoil involve the fields of classical acoustics and fluid mechanics. In this paper, trailing edge noise production is evaluated using empirical model for NACA 0012 and NACA 6320 airfoils. The sound pressure levels from trailing edge surface are calculated for different flow configurations. The growth of boundary layer thickness and displacement thickness, for different chord lengths and Mach numbers with varying angles of attack, is illustrated for NACA 0012. The sound pressure levels were computed numerically between 00 to 60 angles of attack and at constant chord length of 1.2m using Brookes Pope Marcolini method. The results showed a change of ~2-5dB in peak amplitude for mid frequencies region of spectrum. The effects of varying chord length and Mach number on sound pressure levels are illustrated for both airfoils. The relative velocity field for airfoils was computed using the boundary element method. The combined effect of thickness and camber on sound power level is demonstrated at a 40 angle of attack and for a Mach number of 0.191. Validation of sound pressure levels is done based on the results obtained for NACA0012 for similar flow conditions.

Stability of patterns on thin curved surfaces.

We consider reaction-diffusion equations on a thin curved surface and obtain a set of effective reaction-diffusion (R-D) equations to O(ε^{2}), where ε is the surface thickness. We observe that the R-D systems on these curved surfaces can have space-dependent reaction kinetics. Further, we use linear stability analysis to study the Schnakenberg model on spherical and cylindrical geometries. The dependence of the steady state on the thickness is determined for both cases, and we find that a change in the thickness can stabilize the unstable modes, and vice versa. The combined effect of thickness and curvature can play an important role in the rearrangement of spatial patterns on thin curved surfaces.

Combined effects of thickness, grain size and residual stress on the dielectric properties of Ba0.5Sr0.5TiO3 thin films

We studied the microstructure and dielectric properties of Ba0.5Sr0.5TiO3 thin films on polycrystalline alumina substrates with film thicknesses in the range 90–400 nm. Upon annealing at 900 °C in a rapid-thermal-annealing furnace the films crystallized in a pure perovskite phase with uniform and dense microstructures consisting predominantly of columnar grains. As the film thickness increased from 90 to 170 nm, the average lateral grain size increased from 45 to 87 nm. In the same manner, the dielectric permittivity of the films increased from 650 to 1250, measured at 100 kHz and room temperature. In the thickness range between 170 and 240 nm, only a slight change of the grain size and the permittivity was observed. But with a further increase of the thickness to 400 nm the permittivity decreased, even though the grain size remained unchanged. A similar trend was also observed in the GHz range. The reduced dielectric permittivity in the thicker films is related to the tensile residual stress, which develops due to the thermal expansion mismatch between the film and the substrate. The measured tensile residual stress was above 300 MPa in the thickness range 90–170 nm, while it partially relaxed at greater thicknesses because of the formation of cracks. As a result, the dielectric permittivity of the films is reduced.

Dynamic stability of cantilevered functionally graded cylindrical shells under axial follower forces

Flutter of cantilevered, functionally graded cylindrical shells under an end axial follower force is addressed. The material properties are assumed to be graded along the thickness direction according to a simple power law. Using the Hamilton principle, the governing equations of motion are derived based on the first-order shear deformation theory. The stability analysis is carried out using the extended Galerkin method and minimum flutter loads and corresponding circumferential mode numbers are obtained for different volume fractions, length-to-radius, and thicknesses-to-radius ratios. Two different configurations are considered for the FGM: one in which the metal phase is the outer layer and the ceramic phase is the inner one, and the other vice versa. Results indicate the ranges of major influence due to the volume fraction, and the combined effect of thickness and volume fraction on the flutter load. Also, the optimum and critical power parameters between zero and infinity for which the flutter loads are maximum and minimum are determined.

Combined effect of thickness and stress on ferroelectric behavior of thin BaTiO3 films

Thin BaTiO3 (BTO) layers were deposited by magnetron sputtering on a Si substrate between two thin LaNiO3 (LNO) electrodes (LNO/BTO/LNO/Si structure). The thickness of the BTO layer was varied between 35 nm and 1 μm. The stress, dielectric permittivity, and ferroelectric hysteresis loop were measured after deposition and during heating. It was found that the BTO layers are under tensile stress at the Curie temperature. The tensile stress increases with decreasing layer thickness leading to a shift of the Curie point to a lower temperature, a decrease of remanent polarization, and an increase of the coercive field. The effect of tensile stress on the Curie temperature is dominant within a restricted range of stresses between 300 and 450 mega Pascals (MPa), where the Curie temperature decreases linearly by about 0.16 °C/MPa. A good correlation was found between stress and dielectric measurements with respect to the temperature of the Curie point. The ferroelectric hysteresis loops showed that the ferroelectric-paraelectric phase transition starts at the Curie temperature of the BTO layer and continues within a range of temperatures until about the Curie temperature of the bulk BTO material. The ferroelectric behavior indicates dominance of domains within the interior part of the BTO layer and minor contribution of surface domains. The results are compared with a theoretical approach of size-driven phase transition in stress-induced ferroelectric thin films.

Fracture of polybutylene terephthalate (PBT) film

Combined effects of thickness and temperature on essential work of fracture (EWF) of polybutylene terephthalate (PBT) film were studied using single edge notched tension (SENT) and double edge notched tension specimens. It is found that specific essential work of fracture ( w e) for PBT is independent of temperature below T g (≈80 °C), but decreases above T g. Between temperatures 25 and 100 °C, w e was independent of film thickness in the range 0.125–0.375 mm. The specific non-essential work of fracture ( βw p) was temperature and thickness dependent, being greater for the SENT type specimens. Specimen orientation had no influence on w e but strongly affected βw p. It was found that βw p is greater for cracks propagating normal to the extrusion direction as compared to the parallel direction.

Photoreflectance as a non-destructive, room-temperature technique for routine testing of PM–HEMT structures

In the context of a comparative study of MBE and MOCVD PM–HEMT structures on 3″ GaAs substrates, utilization of photoreflectance indicated that the technique can provide substantial information both non-destructively as well as at room temperature. Concentrating on the structure of the photoreflectance trace below 1.4 eV, the technique can provide information on the combined effect of thickness and In composition in the InGaAs quantum well. In particular, photoreflectance was found to be especially useful for mapping the uniformity over a single wafer as well as for mapping the reproducibility from wafer to wafer. Representative, characteristic patterns were consistently observed for MBE-grown layers, distinct from equally characteristic patterns of MOCVD-grown layers. More importantly, these patterns, obtained by room temperature photoreflectance, were found to coincide with those obtained by low temperature photoluminescence. Although the two techniques identify different electronic transitions, room temperature photoreflectance proves to be equally well adapted as an acceptance test for layer uniformity as low temperature photoluminescence. In probing the reason of non-uniformities, however, low temperature photoluminescence does provide more information. Experimental results are presented for both MBE and MOCVD PM–HEMT structures as well as information extracted from their treatment by modeling in the quantum wells.