Off-axis Angle Research Articles

Stray light analysis of catadioptric long-wavelength infrared optical system

A hood for the system is designed for the characteristics of the catadioptric long-wave infrared optical system. The optical mechanical structure model of the system was established in the stray light analysis software Tracepro. The external stray light is analyzed and calculated by ray tracing, and the PST curve of the system is given. According to the thermal noise of the detector and the influence of solar stray light, the requirements of the system PST are proposed. Calculated the stray light of the sky background, the relationship between the thermal noise of the radiation surface of the system reaching the detector target surface and the temperature is given when the temperature range is 260K~320K. The analysis results show that when the off-axis angle is greater than the critical angle of incidence of the sun, the PST value is less than 10-8, which meets the requirements. The heat radiation inside the system also gradually increases with the increase of temperature. To realize the background limit detection of weak targets, the system needs to be cooled.

Tensile Initial Damage and Final Failure Behaviors of Glass Plain-weave Fabric Composites in On- and Off-axis Directions

Mechanical properties and failure behavior of glass plain-weave fabric composites under on-axis (i.e. 0 and 90° direction) and off-axis (i.e. θ=5, 10, 15, 30, 45 and 60°) tensile loading conditions have been experimentally investigated. Acoustic emissions (AE) monitoring and step-by-step optical observation with interrupted tension tests were adopted to study the character and failure mechanisms of various fiber orientations. The experimental results indicate that both off-axis elastic modulus and strength degrade with increasing off-axis angle in all cases. There is a good agreement for the axial modulus Ex between the experimental results and theory results obtained from orthotropic linear elasticity theory. Adoption of the principal shear strength S45°=28.5 MPa which is evaluated using the tensile strength based on the 45° specimen allows better predictions of the off-axis tensile strengths by means of the Tsai-Hill failure criterion. Off-axis specimens exhibit lower knee point stress than on-axis ones and initial fracture strain monitored by AE (>75 dB) has a good fit to knee-point strain in this study. Tensile strength exhibits an increased tendency toward the delay of initial fracture behavior.

In vitro and schematic model eye assessment of glare or positive dysphotopsia-type photic phenomena: Comparison of a new material IOL to other monofocal IOLs

To compare the glare-type photic phenomena for a new intraocular lens (IOL) to other monofocal IOLs, and to investigate how IOL design features might affect these phenomena. Alcon Laboratories, Inc., Fort Worth, Texas; John A Moran Eye Center, University of Utah, Salt Lake City, USA. Schematic model eye evaluation and invitro study. Five monofocal IOL models (Clareon CNA0T0, Tecnis ZCB00, enVista MX60, Eternity W-60, and Vivinex XY1) were used to evaluate glare or positive dysphotopsia-type phenomena. Optical simulations of incoming light were generated using nonsequential ray-tracing software based on a collimated light source for various off-axis angles of illumination. The simulation analyses were verified using a laboratory invitro bench-top glare measurement system. The Clareon and Vivinex IOLs produced focused off-axis images with negligible peripheral glare characteristics. The Tecnis and enVista IOLs produced dispersed images with additional glare characteristics at 45 degrees of off-axis illumination and higher. The Eternity IOL showed the highest edge-reflected glare characteristic, likely because of its straight optic edge geometry. The laboratory bench images and glare intensity profiles were consistent with the simulation data. Invitro and nonsequential ray-tracing evaluations showed that straight optic edges and peripheral nonimaging optic geometry might contribute to positive dysphotopsia. The IOL designs with optic edge curvature and full functional optics demonstrated the lowest level of glare-type photic phenomena. Only clinical studies can confirm whether the differences observed between the IOLs invitro are clinically significant.

Multiscale Analysis of CFRP Laminates with MMF3 Criterion under Different Off-Axis Loading Conditions.

A multiscale analysis strategy with physical modified-micromechanics of failure (MMF3) criterion was proposed to analyze the failure behaviors of carbon fiber reinforced plastic (CFRP) laminates. The quantitative relationship between the macro- and micro- stresses was determined considering two typical fiber distributions. Thermal residual stress was taken into account in the stress transformation. The failures were defined and the properties of damaged elements were degraded at the constituent level. The back-calculation method based on the iteration algorithm was proposed to determine the micro strength with macro mechanical tests. A series of off-axis loading tests were conducted to verify the established multiscale models. The predicted strength was also compared with the results using micromechanics of failure (MMF) criterion to present accuracy improvements. Thermal residual stress was found to affect the strength by contributing to the matrix damage status. Meanwhile, sensitivity analysis was provided for the matrix-dominant micro strength to investigate its physical meaning. Results suggest that the micro tensile and compressive strength of the matrix influenced the off-axis tensile and compressive strengths respectively, with relative large off-axis angles, while the micro shear strength of the matrix dominated when the off-axis angles were relative small.

Trigonometric comparison measure: A feature selection method for text categorization

Text data represented using vector space model is high dimensional data since the number of words can easily grow to tens of thousands for a moderate sized dataset. It may contain lots of redundant or irrelevant features that degrade the performance of a classifier for text categorization. To address this problem, feature selection can be applied for dimensionality reduction and it aims to find a set of highly distinguishing features. Most of filter feature selection methods for text categorization are based on document frequencies in positive and negative classes. Considering only document frequencies favors terms frequently used in a larger class and ignores relative document frequencies in the classes. In this paper, we present a new filter feature selection method, named Trigonometric Comparison Measure (TCM) considering relative document frequencies. The proposed method utilizes true positive rate and false positive rate to determine a better subset of features for text categorization and prefers terms that appear only in documents of one class with high probability. In order to assign a higher rank to terms that are frequently used in one class and rarely appears in another class, TCM calculates off-axis angles of a vector represented as (tpr,fpr) and gives a larger score to terms with a small angle using sin andcos functions. The proposed method is compared with eight well-known filter feature selection methods including balanced accuracy measure (ACC2), information gain (IG), chi-squared (CHI), odds ratio (OR), Gini index (Gini), Deviation from a Poisson distribution (DP), distinguishing feature selector (DFS) and normalized difference measure (NDM) on ten datasets using the multinomial naïve Bayes and support vector machines. The experimental results show that TCM achieves significantly better performance for text categorization.

Flipping interferometry with doubled imaging area.

We present a new external off-axis holographic module that doubles the acquired complex wavefront field of view, based on using both holographic flipping and multiplexing. In contrast to previous designs, this design does not require spatial filtering (no pinhole or lenses) to create the reference beam externally. In addition, the overlap area between the fields of view, as well as the off-axis angle between the sample and reference beams, can be fully controlled. As we demonstrate experimentally, this approach is useful for quantitative phase microscopy of extended stationary and dynamic samples, such as cancer cells during rapid flow and beating cardiomyocytes.

Effects of off-axis angle on shear progressive damage of 3D woven composites with X-ray micro-computed tomography

This paper presents the influence of the off-axis angles on the shear progressive damage of three-dimensional (3D) woven carbon/epoxy composites. Five kind of samples with different angles, 0°, 30°, 45°, 60° and 90°, of the weft and warp yarn orientation are experimentally tested via short beam shear method. X-ray micro-computed tomography (Micro-CT) techniques are employed to identify the internal damage initiation/evolution of 3D woven composites. Results indicate that the off-axis angles have significant effects on the mechanical behaviors, damage change and final failure mechanisms. Furthermore, the ultimate strength of on-axis samples are mainly influenced by the yarn tensile fracture and delamination, whereas those of off-axis samples are largely governed by the debonding and yarn pull-out breakage.

Off-axis bending behaviors and failure characterization of 3D woven composites

This paper presents the influence of the off-axis angles on the flexure behaviors of three-dimensional (3D) woven carbon/epoxy composites. Four kind of samples with different angles, 0 degree, 30 degree, 45 degree and 90 degree, are experimentally tested via three-point bending method. The immersion focused ultrasound imaging and micro-computed tomography (Micro-CT) techniques are employed to investigate the deformation and damage mechanisms in the specimens fractured in bending. Results indicate that the stress-deflections of on-axis (0 degree and 90 degree) samples exhibit obvious quasi-brittle behaviors, whereas those of off-axis (30 degree and 45 degree) samples show important ductile features. Furthermore, the dominant failure mechanism of on-axis samples are identified to be inter-ply delamination and fiber bundle fractures, whereas those of off-axis samples are matrix cracks and tows debonding.

Thermomechanical investigation of unidirectional carbon fiber-polymer hybrid composites containing CNTs

In this research, the thermoelastic response of unidirectional carbon fiber (CF)-reinforced polymer hybrid composites containing carbon nanotubes (CNTs) are analyzed using a physics-based hierarchical micromechanical modeling approach. The developed model consists of a unit cell-based scheme along with the Eshelby method which can consider random orientation, random distribution, directional behavior, non-straight shape of CNTs and interphase region generated due to the non-bonded van der Waals interaction between a CNT and the polymer matrix. The predictions are compared with the experimental data available in the literature and a quite good agreement is pointed out for the fibrous polymer composite, CNT-polymer nanocomposite and fiber/CNT-polymer hybrid composite systems. The influences of several factors, including volume fraction, aspect ratio, off-axis angle and arrangement type of CFs as well as CNT volume fraction on the thermoelastic behavior of CF/CNT-polymer hybrid composites are examined in detail. The results indicate that the transverse CTE of a unidirectional CF-reinforced composite is significantly improved due to the addition of CNTs, while the hybrid composite CTE in the longitudinal direction is negligibly affected by the CNTs. Also, it is found that the role of CNT in the hybrid composite thermoelastic behavior becomes more prominent as the CF aspect ratio decreases.

Failure conditions of solid wood on off-axis compression testing

Abstract Off-axis compression tests (OACT) were conducted on solid wood from six tree species, and the relationship between the off-axis compressive strength (OACStr) and the off-axis angle was predicted under the conventional Hill-type quadratic failure conditions, off-axis special failure conditions, and under a condition proposed in this study, which contains terms of interaction between the normal and shear stresses. The latter was an effective approach for accurately predicting the OACStr, although the physical meaning of the interaction terms is not yet clear. Under the off-axis specialized conditions, the approach was simple and accurate for predicting the OACStr, which includes the 45° off-axis angle.

Microscopic modeling and effective properties evaluation of glass/epoxy plain woven composites

In this study, the description of a micromechanical method to estimate the effective elastic constants of woven composites with polymer matrix is presented. To this end, woven composites are discretized to a series of unidirectional laminas. For validating the microscopic mechanical method, the calculated effective moduli of the unidirectional lamina are compared with other literatures. In addition, the fiber off-axis angle effects on longitudinal modulus, transversal modulus and Poisson’s ratio are further discussed by employing the coordinate transformation formula. It can be concluded that minimum longitudinal modulus will be acquired when the off-axis angle of 60° is considered. Combining with the classic laminate theory and 3D high-fidelity generalized method of cells, the elastic constants of E-glass/epoxy woven composites are predicted. By comparisons, it demonstrated that the proposed method is capable of mechanical modeling for plain woven composites.

Nonlinear Material Model for Quasi-Unidirectional Woven Composite Accounting for Viscoelastic, Viscous Deformation, and Stiffness Reduction.

To clarify the individual contribution of viscoelastic and viscous deformation to the global nonlinear response of composites, multilevel cyclic loading-unloading recovery tensile tests were carried out. The experimental results show that there is a linear relationship between the viscous strain and viscoelastic strain of composites, regardless of the off-axis angle or loading stress level. On the basis of experimental results, a coupled damage-plasticity constitutive model was proposed. In this model, the plasticity theory was adopted to assess the evolution of viscous strains. The viscoelastic strain was represented as a linear function of viscous strains. Moreover, the Weibull function of the effective stress was introduced to evaluate the damage variables in terms of stiffness reduction. The tensile stress-strain curves, predicted by the proposed model, showed a good agreement with experimental results.

The effect of off-axis angles on the mesoscale deformation response and failure behavior of an orthotropic textile carbon-epoxy composite

The deformation response and failure behavior of an orthotropic textile carbon-epoxy composite were investigated under off-axis tensile loading. Digital image correlation (DIC) was utilized to effectively capture the full-field and mesoscale strain distribution. The macroscale mechanical performance was strongly sensitive to the fiber bundles orientation relative to the loading direction. Based on the experimental data, a quantitative relation between the rotation angle and off-axis angle was established, and a negative correlation between the failure strength and the rotation angle was observed. The underlying failure mechanisms of the specimens with different off-axis orientations were analyzed using scanning electron microscopy (SEM) and DIC techniques. The load-bearing mechanisms were different between the on- and off-axis cases. High local shear strain eventually resulted in the brushy shear-type fracture in the off-axis case, and the local micro cracks developed during the loading caused the reduction and imbalance of local load-bearing capacity.

The effect of matrix cracking on mechanical properties in FRP laminates

BackgroundFiber Reinforced Polymer (FRP) laminates have properties, which are highly dependent on the ply fiber orientations and which can be designed for optimum laminate performance. The purpose of this study is to investigate the effect of matrix cracking on the mechanical properties of FRP laminates with various off-axis angles, and to provide a critical test for an analytical solution using variational stress analysis.MethodsCarbon and glass fiber reinforced polymer laminates (CFRP and GFRP) are tested. FRP prepregs are cured by using autoclave method to form laminates with layups [θm/ φn]s. The laminates are then loaded monotonically and cyclically to obtain their mechanical properties and the effect of matrix cracks on the properties. Some of the effects include reduction of laminates’ stiffness and residual strains after unloading. In order to obtain higher crack densities in specimens, artificial cracks method was introduced in this study, where notches were made at the edges of some specimens before tested in tension. Cracks observation for CFRP laminates is done by using the X-ray technique, while for GFRP laminates a DSLR camera is used.ResultsThe measured stiffness reduction as a function of the crack density is compared to an analytical prediction for cracked angle-ply laminates based on a variational stress analysis. The experimental results for stiffness reduction agree well with the analytical results.ConclusionUnderstanding the behavior of damaged laminates with simple configurations, as performed in this study, is of high importance for prediction of damage effects on laminates with more complex configuration, e.g. with quasi-isotropic layups.

Anisotropic in-plane mechanical behavior of square honeycombs under off-axis loading

Square honeycombs show a strong anisotropy when loaded in different orientations. In this paper, a new theoretical approach is proposed to describe the in-plane yield strengths of the square honeycombs in different directions. The analytical solutions are validated by the finite element simulations and the experiments. The results indicate that the in-plane strengths of the square honeycombs show great anisotropy, which can be expressed as functions of the in-plane off-axis angles. The square honeycombs show high yield strengths in the principal directions and low yield strengths in the in-plane off-axial directions. However, the yield strengths in the principal directions under shear loading are much lower than those in the in-plane off-axial directions. In addition, four typical deformation processes are observed both in experiments and numerical simulations when the honeycombs are compressed in different directions. An interesting rotating deformation mechanism is observed in the in-plane off-axial direction compression with small angles. The results of this study are hoped to contribute to develop the in-plane off-axis mechanical properties of honeycombs for the engineering applications.

Failure of cross-ply NCF composites under off-axis compressive loads - An experimental study and a new strength prediction model including fibre bundle waviness

Abstract The design of reliable and efficient mechanical joints with non-crimp fabric (NCF) composites depends on several factors but knowledge on actual loading direction and an accurate compressive strength prediction is essential. Motivated by this, the current study is focused on the compressive strength of cross-ply NCF composites and the influence of fibre orientation in relation to the loading direction. Possible influence of stacking sequence on the compressive strength is also studied. Compression tests of cross-ply NCF composite laminates that are loaded at various off-axis angles are performed and the failure mechanisms are identified. An analytical semi-laminar based model for strength prediction of NCF composite laminates loaded in compression is then suggested. The model take in- and out-of-plane bundle waviness into account. Good agreement between the proposed model and experiments is observed.

Inter-fibre failure of through-thickness reinforced laminates in combined transverse compression and shear load

Extensive studies have been reported on the improvement of through-thickness reinforcement to inter-laminar performance of composite laminates; current understanding on the in-plane performance is relatively limited, although it is also concerned in industrial application. The influence of through-thickness reinforcement (Z-pinning) on the inter-fibre failure in compression of unidirectional laminates was investigated. Both unpinned and Z-pinned laminates were tested at four different off-axis angles, representing different combinations of transverse compression and in-plane shear stress. It was found that the stiffness of Z-pinned laminates decreased significantly in all off-axis angles. The failure strain and strength were reduced in shear dominated failure modes, while improved in the compression dominated failure modes by the presence of the Z-pins. A further investigation on the angle of failure plane was carried out and a comparison with analytical failure models is presented.

Growth, stress, and defects of heteroepitaxial diamond on Ir/YSZ/Si(111)

Basic understanding of the fundamental processes in crystal growth as well as the structural quality of diamond synthesized by chemical vapour deposition on iridium surfaces has reached a high level for samples with (001) orientation. Diamond deposition on the alternative (111) surface is generally more challenging but of appreciable technological interest, too. In the present work, heteroepitaxy of diamond on Ir/YSZ/Si(111) with different off-axis angles and directions has been studied. During the growth of the first microns, strong and complex intrinsic stress states were rapidly formed. They restricted the range of suitable temperatures in this study to values between 830 °C and 970 °C. At low-stress conditions, the maximum growth rates were about 1 μm/h. They facilitated long-time processes which yielded pronounced structural improvements with minimum values of 0.08° for the azimuthal mosaic spread, 4 × 107 cm−2 for the dislocation density and 1.8 cm−1 for the Raman line width. This refinement is even faster than on (001) growth surfaces. It indicates substantial differences between the two crystal directions in terms of merging of mosaic blocks and annihilation of dislocations. Crystals with a thickness of up to 330 μm have been grown. The correlation of photoluminescence and μ-Raman tomograms with topography data also revealed fundamental differences in the off-axis growth between (001) and (111) orientation. Finally, the analysis of the microscopic structures at the growth surface provided the base for a model that can conclusively explain the intriguing reversal of stress tensor anisotropy caused by a simple inversion in sign of the off-axis angle.

Physics potentials with the second Hyper-Kamiokande detector in Korea

Hyper-Kamiokande consists of two identical water-Cherenkov detectors of total 520~kt with the first one in Japan at 295~km from the J-PARC neutrino beam with 2.5$^{\textrm{o}}$ Off-Axis Angles (OAAs), and the second one possibly in Korea in a later stage. Having the second detector in Korea would benefit almost all areas of neutrino oscillation physics mainly due to longer baselines. There are several candidate sites in Korea with baselines of 1,000$\sim$1,300~km and OAAs of 1$^{\textrm{o}}$$\sim$3$^{\textrm{o}}$. We conducted sensitivity studies on neutrino oscillation physics for a second detector, either in Japan (JD $\times$ 2) or Korea (JD + KD) and compared the results with a single detector in Japan. Leptonic CP violation sensitivity is improved especially when the CP is non-maximally violated. The larger matter effect at Korean candidate sites significantly enhances sensitivities to non-standard interactions of neutrinos and mass ordering determination. Current studies indicate the best sensitivity is obtained at Mt. Bisul (1,088~km baseline, $1.3^\circ$ OAA). Thanks to a larger (1,000~m) overburden than the first detector site, clear improvements to sensitivities for solar and supernova relic neutrino searches are expected.

Static Bending and Free Vibration Analysis of Hybrid Fuzzy-Fiber Reinforced Nanocomposite Beam-A Multiscale Modeling

Static and free vibration multiscale analysis of fuzzy-fiber-reinforced composite (FFRC) beam is investigated using a three-dimensional micromechanical model together with two-dimensional elasticity macromechanical theory. In the hybrid nanocomposite, aligned carbon nanotubes (CNTs) are radially grown on the circumferential surfaces of carbon fibers. Influence of the carbon fiber orientation, volume fraction and arrangement; CNT volume fraction and interphase region characteristics on the FFRC beam deflection and natural frequencies are studied. Good agreements are reported for the presented results compared with available experiments and the other modeling strategies at both micro and macro levels. The results reveal that the FFRCs properties are strongly dependent on the carbon fiber off-axis angle. By increasing the off-axis angle from [Formula: see text] to [Formula: see text], the FFRC beam deflection sharply increases up to [Formula: see text] fiber angle and then its value decreases. It is shown that the growth of CNTs on the carbon fiber surface leads to the highest decrease in the beam deflection for 90[Formula: see text] coupon. Also, increasing the interphase thickness decreases the beam deflection and increases the natural frequencies, especially for [Formula: see text] coupon. Moreover, the increasing the interphase Young’s modulus gives maximum 1.74% increase in the natural frequencies.