Off-axis Angle Research Articles

Mechanical properties of phenolic foam composite meta-aramid honeycomb under various directional loads and thermal environments

To enhance the mechanical properties of honeycomb structures, a phenolic foam composite meta-aramid honeycomb core (PFAH) was developed. Experimental, simulation, and theoretical analyses revealed that PFAH increased out-of-plane energy absorption by 89.47% without altering the specific energy absorption of aramid honeycomb, maintaining smooth plastic deformation. At 150 °C, it retained 90.7% of mechanical properties. In the in-plane direction, PF raised plateau stress by 798.73%. The study identified the critical spinodal for off-axis angle deformation modes and established a theoretical relationship between PFAH strength and off-axis angle, demonstrating superior resistance to shallow-angle oblique loading compared to unfilled honeycomb.

Optimizing tensile strength and failure prediction in hemp fiber composites: Coupling effects of microfibril angle and fiber orientation under off-axis loading

In response to environmental concerns associated with synthetic fiber-reinforced materials, plant fiber-reinforced composites are increasingly recognized as a more sustainable alternative. However, predicting the mechanical properties of these composites remains challenging due to the unique microstructure of plant fibers. This study proposes an optimized Tsai-Hill failure criterion that incorporates the microfibril angle (MFA) and fiber orientation to enhance failure predictions. The MFA of hemp fibers was measured using X-ray diffraction (XRD), and the failure mechanisms of unidirectional hemp fiber composites under off-axis tensile stresses were thoroughly analyzed. Experimental results reveal a 10.69 % increase in tensile strength at a 5° off-axis angle compared to the fiber direction. As the off-axis angle increases, the failure mode transitions from fiber fracture and pull-out to matrix tearing and interlayer shear failure. For angles above 10°, the failure stress aligns with both the maximum stress and Tsai-Hill criteria. For angles below 10°, integrating MFA into the Tsai-Hill criterion significantly improves prediction accuracy. These findings offer critical insights for optimizing the tensile performance of hemp fiber composites and predicting their behavior under off-axis loading conditions. Consequently, this study can support the use of hemp fiber composites in a broader range of applications.

The Effects of Loading Angles on the Failure of Cross-Ply Notched Bio-Basalt Composites

A cross-ply basalt V-notched butterfly specimens were subjected to pure tension, combined tension-shear, and shear stress-strain state using a modified Arcan test fixture with loading angles from 0° to 90° with 15° increment. Multiaxial stress and strain states were studied using the principal stress and strain ratio, from which the principal angle was determined and used to represent principal states in the gauge section. The quasi-elastic to non-linear transition stresses were determined for each loading angle. In biaxial stress-strain states and pure shear, the deformation and consequently the shear-induced damage start to accumulate significantly. Also, in biaxial stress-strain states between 15°-75°, the shift from tension-shear to pure shear was observed after the transition to the non-linear part of the stress-strain curve. The digital image correlation (DIC) images and microscopic evaluation show that a large extent of damage is the consequence of the shear deformation after the rotation of 0° clamped fibres, while the 90° fibres maintained their original straight form. In off-axis tests, the principal strain axis rotates towards the weakest material axis even at small off-axis angles. This causes a transition from a tension-shear biaxial state in the linear loading part to shear in the non-linear part, leading to irreversible damage beyond the transition point.

Atmospheric Response for MeV γ Rays Observed with Balloon-borne Detectors

The atmospheric response for MeV γ rays (∼0.1–10 MeV) can be characterized in terms of two observed components. The first component is due to photons that reach the detector without scattering. The second component is due to photons that reach the detector after scattering one or more times. While the former can be determined in a straightforward manner, the latter is much more complex to quantify, as it requires tracking the transport of all source photons that are incident on Earth’s atmosphere. The scattered component can cause a significant energy-dependent distortion in the measured spectrum, which is important to account for when making balloon-borne observations. In this work, we simulate the full response for γ-ray transport in the atmosphere. We find that the scattered component becomes increasingly more significant toward lower energies, and at 0.1 MeV, it may increase the measured flux by as much as a factor of ∼2–4, depending on the photon index and off-axis angle of the source. This is particularly important for diffuse sources, whereas the effect from scattering can be significantly reduced for point sources observed with an imaging telescope.

Effects of off-axis angles of 4H-SiC substrates on properties of β-Ga2O3 films grown by low-pressure chemical vapor deposition

In this work, β-Ga2O3 films with (−201) preferred orientation were heteroepitaxially grown on SiC substrates with off-axis angles of 0°, 4° and 8° by low-pressure chemical vapor deposition (LPCVD). It is found that the crystal quality, surface morphology, electrical properties of the β-Ga2O3 films of the film are significantly sensitive to the off-axis angle of SiC substrates. The crystal quality and surface morphology of the film were significantly improved when the 4° off-axis substrate was used, of which the FWHM (Full width at half maximum) was as low as 0.169° and the Ra (Roughness Average) of the smooth surface was 1.98 nm. Due to the improvement of crystal quality, the Hall mobility of the films deposited on 4° off-axis substrates was increased to 50.88 cm2/V·s. The photoluminescence peak intensity of the film increases first and then decreases with the increase of the off-axis angle of the substrate. However, the use of the off-axis substrate has no obvious effect on the oxygen vacancy ratio of the films. The results of this study demonstrate the significance for the preparation of high quality heteroepitaxial β-Ga2O3 films on SiC substrate for the promising applications in power electronic and optoelectronic devices.

Off-axis mechanical behavior and dynamic characteristics of UHMWPE composite laminates

An understanding of the off-axis mechanical behavior and failure mechanisms of ultra-high molecular weight polyethylene (UHMWPE) cross-ply laminates subjected to quasi-static and dynamic loadings is developed, with focus on the influence of off-axis angle and strain rate. For off-axis tension, UHMWPE laminates exhibit polymer shear response characteristics. An orientation-hardening phenomenon is captured, as fiber rotation leads to local increment of load capacity along the loading orientation. The failure strength presents an evidentially descending trend with off-axis angle from 0° to 45°. A non-monotonic variation of strength with strain rate is further observed: increasing with strain rate up to 500 s−1 but decreasing above, which is attributed to failure mode switching from plastic failure to brittle failure. The Tsai-Wu failure criterion, on homogenized cross-ply laminae, is experimentally modified with rate dependence. Further investigation on detailed information of the unidirectional properties should be conducted with the backing-out scheme to establish unidirectional failure criterion.

Characterization on fibre kinking fracture of laminated composites under combined compression and shear at high loading rate

This paper presented a novel method to characterize the fracture toughness and cohesive law of laminated composites under combined compression and shear at high loading rate. Compact compression specimens with off-axis fibres which introduce the in-plane shear stresses were conducted on the uniaxial bidirectional electromagnetic Hopkinson bar system and the displacement field and strain field were recorded by the high-speed camera for the digital image correlation analysis and J-integral calculation. The results reveal that the in-plane shear stresses bring the increase of fracture toughness at crack initiation and propagation and advance the damage initiation of the specimens. The fracture surfaces indicate that the shear stresses cause the fibre bundles' shear failure during the formation of the kink band, accompanied by more energy dissipation with the increase of off-axis angle.

A 3D Elastoplastic Constitutive Model Considering Progressive Damage Behavior for Thermoplastic Composites of T700/PEEK.

Due to their excellent mechanical properties, the carbon fiber-reinforced polymer composites (CFRPs) of thermoplastic resins are widely used, and an accurate constitutive model plays a pivotal role in structural design and service safety. A two-parameter three-dimensional (3D) plastic potential was obtained by considering both the deviatoric deformation and the dilatation deformation associated with hydrostatic stress. The Langmuir function was first adopted to model the plastic hardening behavior of composites. The two-parameter 3D plastic potential, connected to the Langmuir function of plastic hardening, was thus proposed to model the constitutive behavior of the CFRPs of thermoplastic resins. Also, T700/PEEK specimens with different off-axis angles were subjected to tensile loading to obtain the corresponding fracture surface angles of specimens and the load-displacement curves. The two unknown plastic parameters in the proposed 3D plastic potential were obtained by using the quasi-Newton algorithm programmed in MATLAB, and the unknown hardening parameters in the Langmuir function were determined by fitting the effective stress-plastic strain curve in different off-axis angles. Meanwhile, the user material subroutine VUMAT, following the proposed constitutive model, was developed in terms of the maximum stress criterion for fiber failure and the LaRC05 criterion for matrix failure to simulate the 3D elastoplastic damage behavior of T700/PEEK. Finally, comparisons between the experimental tests and the numerical analysis were made, and a fairly good agreement was found, which validated the correctness of the proposed constitutive model in this work.

On asymmetric failure in additively manufactured continuous carbon fiber reinforced composites

Due to a filament-by-filament and layer-by-layer structure produced by an additive manufacturing (or namely 3D printing) technique, mechanical properties of 3D printed materials diverge considerably from those of carbon fiber reinforced polymer (CFRP) composites made by traditional processes. This study aims to experimentally characterize their mechanical properties through the off-axis tensile, compressive and V-notch shear tests. Advanced imaging techniques, such as digital image correlation (DIC), scanning electron microscopy (SEM) and computed tomography (CT), are used to investigate anisotropic nature of materials and failure mechanisms of the 3D printed CFRP composites. The applicability of conventional failure criteria to the 3D printed CFRP composites, including Tsai-Wu, Tsai-Hill, Hoffman, Maximum Stress, Hashin, Puck and LaRC05, is assessed systematically. The experimental results divulge that the filament-by-filament and layer-by-layer features intrinsic to 3D printed CFRP composites lead to an uneven yet organized distribution of voids. This characteristic contributes on the development of claw mark strain patterns, parallel track inter-fiber failure patterns, and distinct compression failure modes such as delamination and interlayer crack under loading perpendicular to the fiber direction. The voids in the 3D printed CFRP materials are partially responsible for the significant asymmetry when off-axis angle increases. Notably, the conventional failure criteria exhibit limited capability for predicting the off-axis tensile strength accurately. This phenomenon can be attributed to the redistribution of inherent fiber waviness as the fiber encounters tensile loads. Based on the experimental results, the inter-fiber failure as per the LaRC05 is modified to obtain an enhanced failure criterion for predicting the off-axis tensile strength. This study is expected to provide fundamental understanding of structural characteristics and mechanical properties for 3D printed CFRP composites.

Coupling effect of temperature and off-axis angle on the compressive properties of needled carbon/quartz fiber-reinforced phenolic resin composite

Studying high temperature off-axis compression of composites is key for advancing aerospace, optimizing designs, and developing innovative materials. For this objective, the impact of temperature and off-axis angle (denoted as θ) on the compressive properties of needled carbon/quartz fiber-reinforced phenolic resin (CF-QF/PF) composite has been explored. Initially, the thermal behavior of the materials was assessed through thermogravimetric (TG) analysis, followed by 25 sets of static compression tests across five off-axis angles at five temperatures. Subsequently, a model was applied to predict the strength and modulus under high temperature off-axis compression, with an average error of less than 1 %. The coupling failure mechanisms were then analyzed through various microscopic observations. The findings indicate that when T = 400 °C, temperature exposure reduces modulus and strength to 0.43 and 0.32 of their normalized values, respectively. Such findings suggest temperature has a more significant impact on strength. Meanwhile, TG results provide evidence for the significant property loss when T = 400 °C. A specific combination of temperature and off-axis angles will lead to a more pronounced reduction in strength and an increase in failure strain, while such an effect on modulus is less significant. Post-mortem analysis reveals that temperature contributes to matrix softening and weakening of the fiber-matrix interface. Compared to specimens with θ = 90°, others exhibit more frequent fiber bundle cracks and microcrack propagation along the fiber-matrix interface, adversely affecting their high temperature performance.

Sn-doped β-Ga2O3 thin films grown on off-axis sapphire substrates by LPCVD using Ga-Sn alloy solid source

Adopting low pressure chemical vapor deposition (LPCVD), Sn-doped β-Ga2O3 thin films were heteroepitaxially grown on c-plane sapphire substrates with off-axis angles towards 〈11–20〉 direction. The influences of off-axis angle on crystal structures, electrical properties, surface morphology, and chemical compositions were thoroughly investigated. As a result, the crystallinity of the β-Ga2O3 films is improved with increasing off-axis angles because in-plane rotational domains are effectively suppressed, demonstrating a full width at half maximum (FWHM) down to 0.64°. Correspondingly, the Hall carrier mobility is promoted from 4.7 to 17.9 cm2/V·s at carrier concentration of 9 × 1017 cm−3, which is believed highly competitive among reported Sn-doped β-Ga2O3 films by LPCVD. These results demonstrate an alternative pathway to heteroepitaxially grow high electrical quality n-doped β-Ga2O3 films for the advancement of Ga2O3 materials and devices.

Multiaxial yield behavior of 2D re-entrant auxetic cellular materials

A series of re-entrant honeycombs (RH) with different off-axis angles and perturbation parameters are constructed and utilized to numerically explore the multiaxial yield behavior for 2D auxetic cellular materials. The off-axis angle significantly affects the anisotropic properties and Poisson's ratio of RH. The effects of microstructural irregularity on the multiaxial yield surfaces are also evaluated for all of the topologies. Simulation results under principal stress space, mean stress-effective stress space and normal stress-shear stress space reveal that the unique microstructure of auxetic cellular materials makes its mechanical properties significantly different from conventional cellular materials with positive Poisson's ratio. Furthermore, a pressure-dependent anisotropic phenomenological yield criterion is proposed for 2D auxetic cellular materials, which can effectively capture the multiaxial yield behavior of RH with different topologies in principal stress space. The present conclusions provide fresh insights into the microstructural design of auxetic cellular materials and pave the way for their future engineering applications.

Experimental Investigation of Mechanical Properties and Failure Mechanisms in Jute-Polyester Composite Laminates under Off-Axis Tensile Loading

Abstract This study focuses on the experimental investigation of the mechanical properties and failure mechanisms of jute-polyester composite laminates under off-axis tensile loading. Various off-axis tests were conducted to analyze the effects of different fiber orientations (0°, 15°, 30°, 45°, 60°, 75°, and 90°) with respect to the load direction. The experimental results revealed a decrease in both off-axis strength and elastic moduli as the off-axis angle increased. Notably, the 45° off-axis tests exhibited the lowest tensile strength and modulus, indicating a more ductile behavior with the highest failure strain. The tensile stress-strain relationship exhibited a nonlinear behavior during off-axis tension loading. Failure analysis was performed using the Tsai-Wu criteria, considering various values of the interaction coefficient F12. The tensile strength and modulus predicted by the Tsai-Wu criteria demonstrated a good correlation with the experimental results. Consequently, the Tsai-Wu criterion proves effective for analyzing the failure properties of woven fabric composites under multiaxial stress conditions.

Fatigue Behavior of Carbon Fiber Woven Composite Laminates with Different Off-Axis Angles Studied by Combining Infrared Thermography

Fatigue Behavior of Carbon Fiber Woven Composite Laminates with Different Off-Axis Angles Studied by Combining Infrared Thermography

Anti-reflection coating with mullite and Duroid for large-diameter cryogenic sapphire and alumina optics.

We developed a broadband two-layer anti-reflection (AR) coating for use on a sapphire half-wave plate (HWP) and an alumina infrared (IR) filter for the cosmic microwave background (CMB) polarimetry. Measuring the faint CMB B-mode signals requires maximizing the number of photons reaching the detectors and minimizing spurious polarization due to reflection with an off-axis incident angle. Sapphire and alumina have high refractive indices of 3.1 and are highly reflective without an AR coating. This paper presents the design, fabrication, quality control, and measured performance of an AR coating using thermally sprayed mullite and Duroid 5880LZ. This technology enables large optical elements with diameters of 600mm. We also present a thermography-based nondestructive quality control technique, which is key to assuring good adhesion and preventing delamination when thermal cycling. We demonstrate the average reflectance of about 2.6% (0.9%) for two observing bands centered at 90/150 (220/280) GHz. At room temperature, the average transmittance of a 105mm square test sample at 220/280GHz is 83%, and it will increase to 90% at 100K, attributed to reduced absorption losses. Therefore, our developed layering technique has proved effective for 220/280GHz applications, particularly in addressing dielectric loss concerns. This AR coating technology has been deployed in the cryogenic HWP and IR filters of the Simons Array and the Simons observatory experiments and applies to future experiments such as CMB-S4.

Research on Off-axis Aberration Optimization Model for Bifocal Glass Lens

Presbyopia entails the gradual deterioration of the eye’s ability to focus, and bifocal lenses have become a common remedy to alleviate blurred near vision and counteract eye strain induced by prolonged usage. The refractive index and Abbe number of these lenses play a crucial role in precisely correcting focal points within the near vision range. Nevertheless, when light rays approach the lens at off-axis angles or with tilts, aberrations occur, often with uneven distribution across real glass materials. The amalgamation of bifocal lenses further compounds the complexity of these aberrations. To enhance the correction of aberrations in bifocal glass lenses, distortion and astigmatism aberration serve as input parameters to calculate the optical quality assessment of the lenses. This study introduces a novel approach to optimize the pairing of bifocal glass lenses through the Taguchi method and fuzzy inference. The experimental design involves the application of the LS9 orthogonal array, streamlining the number of experiments while upholding the reliability of experimental data. The objective is to refine the selection of glass lenses and successfully devise an optimized design model that can be effectively applied to the configuration of bifocal glass lenses.

Characterizing damage patterns and evolution in Multi-Hole GLARE laminates under tensile load via integrated AE and DIC techniques

In this study, a combined numerical simulation and experimental approach was employed to investigate the mechanical behavior and damage mechanisms of multi-hole GLARE laminates with varying off-axis angles under static tensile loading. Digital image correlation techniques were used to monitor changes in the strain field near the open hole region. The acoustic emission parameters were used to recognize damage patterns and evolution. The progressive damage evolution processes of various GLARE components were investigated using a 3D finite element model (FEM) based on the Hashin strain criterion and cohesive zone modeling. The results indicate that GLARE experiences damage modes such as aluminum alloy breakage, matrix cracking, fiber/matrix debonding, delamination, and fiber breakage. The frequency ranges associated with the five damage modes are as follows: [0–50 kHz], [100–175 kHz], [175–220 kHz], [220–300 kHz], and [300–400 kHz]. The dominant damage mode throughout the tensile phase is matrix cracking, but the ultimate failure of the specimen is determined by aluminum alloy breakage and fiber breakage. In addition, increasing the off-axis angle of the multi-hole leads to a shift in the final failure mode from tensile-dominated to tensile shear-dominated, while also slightly reducing the overall initial stiffness of the specimen.

Study on tensile performance of welded seams of PVC coated fabric membrane under uniaxial cyclic load

The mechanical performance degradation of welded seams under cyclic loading may lead to the failure of membrane structures. To investigate the influence of the off-axis angle and the the welded width on mechanical performance, the elastic modulus, ratcheting strain, residual strain and strain energy were studied based on the uniaxial cyclic tensile tests of welded seams. The results show that the elastic modulus of the welded seam specimens shows obvious anisotropy under cyclic loading, and the welded width has the greatest influence on the elastic modulus of the welded seam specimens with 15° and 75° off-axis angles, under which off-axis angle the welded seam specimens have good recoverability. The irreversible plastic strain of the axial welded seam specimens is close to that of the membrane specimen. The plastic development of the specimen is obvious under large off-axis angles (30°, 45°, 60°), and the final residual displacement of the welded seam specimens reach 3%–4%.

Distribution of basal plane dislocations in 4-degree off-axis 4H-SiC single crystals

The basal plane slip model in 4H-SiC was developed to investigate the effects of off-axis angles on total resolved shear stress. The results showed that the TRSS changed from 6-fold to 4-fold symmetry with the increasing off-axis angles.

Comprehensive study of the off-axis mechanical behaviors of a Polytetrafluoroethylene‐ coated fabric after 23 Years of service at Shanghai stadium

Coated fabrics can experience mechanical performance degradation due to environmental factors and long-term stress during service. Hence, studying the mechanical behaviors of these materials after aging is crucial. While PTFE (polytetrafluoroethylene)-coated fabrics are more commonly used than PVC (polyvinyl chloride)-coated fabrics, limited research exists on their performance after aging in practical engineering applications. PTFE-coated fabrics are primarily used in large-span fabric structures, where their mechanical performance under tensile-shear stress is crucial. This study aims to investigate the mechanical behaviors of PTFE-coated fabrics after practical aging under tension-shear stress. Test materials included decommissioned Saint-Gobain Sheerfill-II PTFE-coated fabrics, which had served for 23 years at Shanghai Stadium, and identical new fabrics. Monotonic tensile, central tearing, and cyclic tensile tests were conducted at seven different off-axis angles to compare the mechanical properties of aged fabrics with new fabrics, including tensile strength, tearing strength, modulus of elasticity, and ratcheting strain. Additionally, this study explored changes in failure mechanisms, tearing mechanisms, applicability of strength criteria, and suitability of the orthotropic model after aging. This provides a comprehensive understanding of the mechanical behaviors of aged PTFE-coated fabrics and valuable insights for engineering design.