Through-thickness Direction Research Articles

Forced vibration analysis of anisotropic curved panels via a quasi-3D model in orthogonal curvilinear coordinate

The present work involves a quasi-3D model in curvilinear coordinate to analyze time-dependent transversal deflection in aragonite curved nano-size panels. Eringen nonlocal deferential model has supported the small-scale phenomenon in nano-sized structures. To predict the effective elastic matrix ingredients in functionally graded aragonite panels, a function reported for anisotropic materials with an exponential variation in elastic properties through-thickness direction are utilized. Then, governing motion equations accounting for fourfold coupled (axial-shear-bending–stretching) components are gained on the basis of Hamilton statement and solved for simply-supported curved panel analytically. Ultimately, the sensitivity of transversal deflection and stresses to exponential factor, geometrical conditions, different curves, and nonlocality versus time are discussed in detail This work also supports a comparison between anisotropy and isotropic approximation to quantify the accuracy of replacing models to decrease the complexity; the differences in central deflection can grow up to 15%.

The effects of compaction and interleaving on through-thickness electrical resistance and in-plane mechanical properties for CFRP laminates

The electrical conductivity of carbon fibre reinforced polymer (CFRP) laminates has previously been shown to be significantly improved by using different electrically functionalized interleaves - Functional Interleave Technology (FIT), particularly in through-thickness direction. Here, the mechanism of FIT is explored via the influence of compaction and interleaving of nickel plated polyester non-woven veils (NPVs) on through-thickness electrical conductivity and in-plane mechanical properties for the CFRP laminates are investigated. The through-thickness electrical property is found to be dominated by the electrically conductive network elements (carbon fibres) and components (carbon fibre layers and NPV layers), which, in turn, is strongly affected by compaction. By using the highly conductive NPVs, the through-thickness resistivity for cured FIT laminates was consistently lowered from 9.3 Ω⋅m to 0.48 Ω m and 1.54 Ω⋅m to 0.016 Ω m for 56% and 64% carbon fibre volume fraction laminates, respectively. The conductive mechanism of FIT specimens follows the series-resistor model, providing the potential to predict the through-thickness electrical conductivity (TTEC) value by interleaving the desired number of NPV layers. Investigation of in-plane mechanical properties indicates the flexural properties and interlaminar shear strength (ILSS) are less affected by compaction. Meanwhile, a 20% reduction of ILSS for FIT laminates is detected because of the lower intra-ply shear resistance of NPV layers.

Degradation mechanisms in carbon fiber–epoxy laminates subjected to constant low-density direct current

This paper reports on an experimental investigation on the mechanical degradation of carbon fiber reinforced composites (CFRP) subjected to long-term exposure of low-density electric field by passing direct current (DC) through cross-ply laminates. In this study, an in-house fabricated experimental setup is used to study the effects of long-duration electrical conduction through cross-ply CFRP laminates. The experiments are conducted under constant current conditions. The change in laminate resistance is measured by monitoring the voltage across the specimen. Meanwhile, the effects of Joule heating are measured by monitoring the surface temperature across the length of the composite sample. Both voltage and temperature measurements are made continuously through the duration of the experiment. Experiments are conducted for continuous three (3) and twenty-four (24) hour duration and for cyclic three-hour repeated duration. Combined loading-compression (CLC) mechanical testing, ultrasonic pulse-echo test and dynamic mechanical analysis (DMA) is performed after electrical degradation to quantify mechanical and thermo-physical changes in the material. It is found that the electrical degradation leads to a 13%–15% reduction in compressive strength , 6%–7% reduction in Young’s modulus in thickness direction, 3%–4% decrease in glass transition temperature , and 41%–45% increase in tan δ . Post-degradation electrical resistivity change in through-thickness and in-plane directions is also correlated to damage. Comparison of change in resistivities of electrically degraded samples to thermally loaded samples indicates that the primary degradation is in the form of delamination caused by Joule heating and localized dielectric breakdown of epoxy near the carbon fiber–epoxy interface. Additionally, X-ray computed tomography (CT) images confirm that damage accumulated in electrically degraded samples is a combination of thermal damage due to Joule heating and dielectric degradation between plies due to passage of electric current.

A composite electrode model for lithium-ion batteries with silicon/graphite negative electrodes

Silicon is a promising negative electrode material with a high specific capacity, which is desirable for commercial lithium-ion batteries. It is often blended with graphite to form a composite anode to extend lifetime, however, the electrochemical interactions between silicon and graphite have not been fully investigated. Here, an electrochemical composite electrode model is developed and validated for lithium-ion batteries with a silicon/graphite anode. The continuum-level model can reproduce the voltage hysteresis and demonstrate the interactions between graphite and silicon. At high states-of-charge, graphite provides the majority of the reaction current density, however this rapidly switches to the silicon phase at deep depths-of-discharge due to the different open circuit voltage curves, mass fractions and exchange current densities. Furthermore, operation at high C-rates leads to heterogeneous current densities in the through-thickness direction, where peak reaction current densities for silicon can be found at the current collector–electrode side as opposed to the separator–electrode side for graphite. Increasing the mass fraction of silicon also highlights the beneficial impacts of reducing the peak reaction current densities. This work, therefore, gives insights into the effects of silicon additives, their coupled interactions and provides a platform to test different composite electrodes for better lithium-ion batteries.

Thermal Diffusivity Measurement in Through-Thickness Direction of Dielectric Film With Metal Substrate

Thin polymer films are widely used as dielectrics in devices operating in the field of electrical engineering, and thermal diffusivity <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${D}$ </tex-math></inline-formula> in through-thickness direction is one of their crucial thermophysical parameters concerned with heat dissipation within the involved devices. However, there exist some difficulties in precisely measuring the thermal diffusivity of micron-thick dielectric film. Considering that the measuring principle of thermal pulse method (TPM) for mapping space charge profile is strongly related to the thermal diffusivity of the film sample, a novel method is proposed to retrieve the coefficient based on the data analysis of the thermal response current of thin polymer dielectric film with a thermally conductive substrate. Experimental results of presentative polymer products biaxially oriented polypropylene (BOPP) and polyimide (PI) films with thickness of several micrometers show well consistency with the data in the literature, demonstrating the feasibility of the proposed method.

In-situ high-energy X-ray diffraction and crystal plasticity modeling to predict the evolution of texture, twinning, lattice strains and strength during loading and reloading of beryllium

Deformation behavior of beryllium during compressive loading and cross-reloading is studied using in-situ high energy synchrotron X-ray diffraction microscopy and crystal plasticity modeling. The evolution of texture, twinning, elastic lattice strains, and flow stress are measured and compared with the predictions of an advanced elastic-plastic self-consistent (EPSC) crystal plasticity model. The model is initialized with the experimentally measured texture and residual stress produced by a simulation of cooling and calibrated to establish a set of model parameters using a portion of the measured data. The rest of the measured data is used for validation of the model. It is shown that the model is sufficiently flexible to reproduce the particularities pertaining to the complex strain-path-change and strain rate sensitive deformation of the material including the evolution of texture, twinning, lattice strains, transients in the stress-strain response, and anisotropic hardening with great accuracy using a single set of model parameters. From the comparison of the experimental data and predictions, we infer that the shifts in active deformation mechanisms between the slip systems from soft to hard and vice versa as well as between twinning to de-twinning are primarily responsible for drastic changes in the flow stress from one path to another. In particular, deformation twins form during compressive in-plane loading followed either by de-twinning during compressive cross-reloading in the through-thickness direction or by forming additional twin variants with some de-twinning of the existing variants during a compressive cross-reloading in another in-plane direction. The shifts in active deformation mechanisms are a consequence of changes in texture relative to the compression direction mediated with the deformation history and strain rate dependent dislocation density evolution governing hardening. The secondary effects improving the predictions come from accounting for residual stress, slip system-level backstress, and latent hardening.

Constraint effect on fracture toughness resistance curves of an X60 pipe steel

The fracture toughness resistance curve (e.g. J-R curve and crack tip opening displacement (CTOD) or δ-R curve) is important in facilitating strain-based design and integrity assessment of oil and gas pipelines, where influence of ground movements and presence of planar weld flaws must be accounted for. In this paper, duplicate single edge bend (SE(B)) and clamped single edge tension (SE(T)) specimens with two different initial crack sizes were prepared from an X60 pipe steel. The longitudinally-oriented specimens were notched in the through-thickness direction and experimentally tested at room temperature. In general, the results showed the expected trends of higher resistance curves for both shallow-cracked versus deeply-cracked specimen types and tension versus bending loading modes. Eleven constraint parameters (i.e. QHRR, QSSY, QLM, QBM, A2, A2BM, h, Tz, Cp, Ap, Vp) were calculated based on three-dimensional (3-D) finite element analyses (FEA) for various tested SE(B) and SE(T) specimens.The results and analysis indicated that the shallow-cracked SE(B) specimens exhibited a constraint condition similar to the intrinsically low-constraint deeply-cracked SE(T) specimens. Among all of the constraint parameters, the Ap parameter based on the normalized equivalent plastic strain contour was found to have the most promising trend in terms of correlating the material’s toughness to constraint level for currently tested specimens. Further on-going investigations are underway to extend the evaluation to resistance curves for specimens made from X100, X80 and X70 pipe steels to allow for the characterization of strain hardening effect, as well as the evaluation of their associated weld metals and heat affected zones (HAZs).

Crack suppression in glass epoxy hybrid L-bend composites through drawdown coating technique using nano and micro fillers

L-bend composite laminates are fundamentally weak against the crack growth in the through-thickness direction, particularly at the curvature region. To deal with this problem, an effort was made to suppress the crack growth by incorporating MWCNT, Al2O3, and SiC Micro fillers at the interface of unidirectional (UD) Glass fiber lamina, using a draw-down coating technique. The L-Bend Glass-Epoxy (GE) laminates were manufactured with the aid of a Hot pressing machine with a holding time being 10 min. The laminates were prepared with a manufacturing temperature of 130 °C and a pressure of 10 kg/cm2. GE curved laminates added with Nano and Micro fillers in the range of 0.5–2 wt% were manufactured. Four-point bending fixtures were designed and manufactured to facilitate the holding and loading of the specimen in the uni-axial tensile machine. Tests were conducted in accordance with ASTM D6415 and load-displacement plots were carefully recorded.GE laminates added with 0.5 wt% fillers greatly influence Curved Beam Strength (CBS) and interlaminar stresses for delamination as compared to pristine GE laminates. The laminates loaded with 0.5 wt% SiC exhibited higher interlaminar radial stresses (108.6 MPa) compared to other GE laminates.

Characterization of Anisotropic Mechanical Properties of X70 Spiral Welded Steel Pipes

Abstract Anisotropic tensile and compressive properties of base metals and girth welds of two API X70 spiral welded pipes have been investigated in this study. Spiral welded pipes exhibit different characteristics of anisotropy from UOE pipes, as the anisotropic property is determined by the thermo-mechanical rolling process of plates and coils produced for pipes. Spiral pipe steels have the lowest strengths in the pipe's transverse direction, contrary to UOE pipes with high strengths in the transverse direction. Yield strengths measured from tensile and compressive tests and their anisotropic characteristics are comparable, although tensile yield strengths are somewhat greater. The results of compressive tests also indicate an anisotropy in the pipe's through-thickness orientation as well as in the longitudinal orientation; yield strengths are highest in the through-thickness direction for both base metals and girth welds of the two pipes.

Effect of heat transfer channels on thermal conductivity of silicon carbide composites reinforced with pitch-based carbon fibers

In this study, silicon carbide (SiC) composites reinforced with pitch-based carbon fibers and composed of heat transfer channels were fabricated by combining chemical vapor infiltration and reactive melting infiltration method. It was observed that the internal heat conduction skeleton of pitch-based carbon fibers was sequentially formed. The thermal conductivities from room temperature to 500 °C along through-thickness direction and in-plane direction were investigated. The results showed that Cpf/SiC composites with heat transfer channels possessed excellent thermal conductvity in two directions, and the thermal conductivity increased with increasing volume content of heat transfer channels. The thermal conductivity in through-thickness direction reached 38.89 W/(m·K), and that for in-plane direction reached 112.42 W/(m·K). Theoretical calculations were empolyed to study the temperature dependence of the Cpf/SiC composites. The variations in slope A′ and intercept B′ values of fitted curves were in good agreement with the experimental results. To verify the reliablilty of the theoretical model, the Cpf/SiC composites were heated at 1650 °C for 2 h and the thermal conductivity exhibited further improvement due to the formation of more perfect crystalline structure. Thermal conductivity through thickness direction improved to 43.49 W/(m·K), and that in in-plane direction improved to 142.49 W/(m·K), which could be identified by the theoretical model. Finally, the leading edge model was established by using ABAQUS finite element analysis software to evaluate the potential application of the composites. Owing to the outstanding thermal conductivity, the leading edge obtained by using Cpf/SiC composites in this study exhibited lower temperature gradient and a more uniform temperature distribution. Moreover, less thermal stress and displacement were generated during heating process.

Electrical properties of 3D printed continuous carbon fibre composites made using the FDM process

Fused deposition modelling (FDM) is an additive manufacturing process for the 3D printing of continuous fibre-thermoplastic composite laminates. The electrical conductivity of continuous carbon fibre (CF)-nylon filaments and laminates printed with a Markforged MarkTwo® FDM machine is experimentally investigated. The axial electrical conductivity of single filaments measured before, during and following the FDM process reveal a large reduction (∼40%) due mostly to breakage of carbon fibres. The electrical conductivity of 3D printed laminates made by the layer-by-layer deposition of the single filaments were determined in the longitudinal, transverse and through-thickness directions, and compared to the electrical properties of a hot moulded composite with a near-equivalent carbon fibre content. The longitudinal conductivity of the 3D printed laminate was only ∼50% that of the hot moulded composite, and this was due mostly to fibre breakages caused by the FDM process. However, the transverse and through-thickness electrical conductivities of the 3D printed laminate were higher (∼13 times and ∼3 times, respectively) than the hot moulded composite due to higher fibre waviness causing increased fibre-to-fibre contact which aids the flow of electrical current in these two directions.

Prediction method for propagating crack length of carbon-fiber-based composite double cantilever beam using its electromechanical behavior and particle filter

Prognostics and health management (PHM) algorithms to predict the electromechanical behavior of double cantilever beam (DCB) composites were proposed using the particle filter method, which is a physics-based prognostics tool. The composites consisted of carbon fibers and carbon-glass hybrid fibers, whose warp and weft were carbon and glass fibers, respectively. The electrical resistance was changed by mechanical deformation as the cracks propagated. Finite element analysis (FEA) supported the empirical data in that mechanical stress along the through-thickness direction of each section and a detour of the electrical path via the crack tip caused resistance changes. Previous prognostics research which used data-driven or physics-based prediction were limited to predict future material behavior in real time due to long calculating time or high dimensional physical model. To develop the real time prognostic tool, the particle filter required sectioning and guiding, even though it only analyzed numerical values with a given physical equation. The sectioning and guiding processes were based on the empirical analysis and the FEA results. The handling was optimized by controlling the number of sections and coefficients of the physical equation. Therefore, this study successfully extracted the remaining useful lifetimes of composites within 4.54% and 5.71% of prediction error for carbon fiber and carbon-glass hybrid fiber based DCB composites, respectively.

Toward Elucidating the Physiological Impacts of Residual Stresses in the Colorectum.

Irritable bowel syndrome afflicts 10-20% of the global population, causing visceral pain with increased sensitivity to colorectal distension and normal bowel movements. Understanding and predicting these biomechanics will further advance our understanding of visceral pain and complement the existing literature on visceral neurophysiology. We recently performed a series of experiments at three longitudinal segments (colonic, intermediate, and rectal) of the distal 30 mm of colorectums of mice. We also established and fitted constitutive models addressing mechanical heterogeneity in both the through-thickness and longitudinal directions of the colorectum. Afferent nerve endings, strategically located within the submucosa, are likely nociceptors that detect concentrations of mechanical stresses to evoke the perception of pain from the viscera. In this study, we aim to: (1) establish and validate a method for incorporating residual stresses into models of colorectums, (2) predict the effects of residual stresses on the intratissue mechanics within the colorectum, and (3) establish intratissue distributions of stretches and stresses within the colorectum in vivo. To these ends we developed two-layered, composite finite element models of the colorectum based on our experimental evidence and validated our approaches against independent experimental data. We included layer- and segment-specific residual stretches/stresses in our simulations via the prestrain algorithm built into the finite element software febio. Our models and modeling approaches allow researchers to predict both organ and intratissue biomechanics of the colorectum and may facilitate better understanding of the underlying mechanical mechanisms of visceral pain.

Polyaniline doped graphene thin film to enhance the electrical conductivity in carbon fiber-reinforced composites for lightning strike mitigation

Multifunctional carbon fiber-reinforced polymer (CFRP) composites are promising structural materials for lightweight applications. However, the low conductivity in the through-thickness direction of the composites limits its applications in the fields that require the high stability of composite against lightning strikes. This work presents the study on the synergetic effect of conducting polymer, polyaniline (PANI), and graphene nanoplatelets (GNP) for increasing the electrical conductivity of CFRP composites. PANI doped GNP flexible film is fabricated with the aid of compatible polymer polyvinylpyrrolidone (PVP), and its effect on the electrical conductivity of CFRP composites has been studied. About 250% in through-thickness conductivity has improved with 11 wt% GNP as a function of the composite. The incorporation of conductive film not only increases the conductivity of the CFRP laminates but also enhances the resistance against lightning strikes. Scanning Electron Microscopy (SEM), Thermogravimetric Analysis (TGA), three-point bending tests were used to analyze the morphology, thermal stability, and mechanical strengths of the composites. Finally, the observation of post-strike damage confirms the importance of through-thickness conductivity for mitigating the lightning strike damage.

Dispersion of guided-waves in heterogeneous and anisotropic elastic plates: A probabilistic approach

In this paper, we present a new approach to study Lamb-type waves of anisotropic elastic plates in a probabilistic framework. The study and analysis are carried out on an elastic plate whose randomly varied elastic properties in the through-thickness direction. By introducing a stochastic model for quantitative description of heterogeneous elastic properties in the plate, the effect of material heterogeneity on Lamb modes may be investigated from a stochastic point of view. To the our best knowledge, this study is the first to investigate Lamb-type waves in a probabilistic framework. Different plate thicknesses are considered and associated dispersion curves are computed. A sensitivity study is performed, highlighting effect of the uncertainty of elasticity properties on the fluctuation of Lamb modes via phase velocities, energy velocities and modes shapes. Next, we discuss the relevance of introducing random media to identify branches associated with experimental dispersion curves.

Free vibration analysis of carbon nanotube RC nanobeams with variational approaches

There is not enough mixed finite element method (MFEM) model developed for dynamic analysis of carbon nanotube reinforced (CNTRC) composite beams in the literature. In the present study, free vibration analysis of functionally graded carbon nanotube reinforced composite (FG-CNTRC) nanobeams is carried out in the framework of variational formulations. The rule of mixture is employed to estimate the effective material properties of single-walled CNT reinforced nanobeams. Four kinds of CNT distribution of un-axially aligned reinforcement material are investigated in the through-thickness direction of the nanobeams. There are the uniform distribution (UD) and functionally graded distributions FG-O, FG-X and FG-Ʌ of CNTs in the thickness direction of the nanobeams (z axis direction) are assumed here for the analysis. The Hamilton

Simulated lightning strike investigation of CFRP comprising a novel polyaniline/phenol based electrically conductive resin matrix

Traditional carbon fiber reinforced plastics (CFRPs) have been reported to exhibit lower electrical conductivity in the through-thickness direction, and have since paved the path for developing new resin systems to improve the through-thickness electrical conductivity and functionality of CFRP laminates. This study designs and investigates a novel Polyaniline (PANI)/Phenol resin, which possesses high electrical conductivity and mechanical strength. The CFRP manufactured by this PANI/Phenol resin with an addition of up to (~23.30%) phenol resulted in 0.6 S/cm through-thickness conductivity and demonstrated flexural strength and modulus values of 477 MPa and 59.2 GPa, respectively. We further evaluate the effectiveness of lightning strike protection of PANI/Phenol-based conductive CFRP laminates with a simulated lightning strike test. In essence, this research reports on PANI/Phenol-based CFRP's effectiveness as a material for lightning suppression without applying traditional metal-based lightning strike protection (LSP) systems.

Characterization of inhomogeneous microstructure and mechanical property in an ultra-thick duplex stainless steel welding joint

Ultra-thick duplex stainless steel welding plates are widely used in various industries. However, one of the significant concerns is the inhomogeneous microstructure and mechanical properties along the thickness, which reduces welding efficiency and degrade service performance. In this study, a 55 mm thick duplex stainless steel welding joint with an X-type weld groove was prepared to study the variation of microstructure and mechanical properties along the through-thickness direction by both the miniature tensile specimen and cross-weld tensile specimen. The correlation between the microstructure and mechanical property was also studied. The results showed that the weld metal was characterized by abundant columnar grains with decreasing austenite content from surface to mid-thickness. Besides, the total fraction of low angle grain boundaries increased more than one-fold, while the total fraction of high angle grain boundaries decreased from 48.03% to 4.52% with increasing depth to the mid-thickness. Furthermore, substantial substructured grains and recrystallized grains were dominated in the weld metal and base metal. Along the thickness direction, the mechanical strength almost decreased and the elongation of welding joint increased with the increasing distance from the surface. Microhardness had a similar trend to that of strength, which all can be attributed to the variation of austenite content and grain boundary character distribution. Along the transverse direction, weld metal had the highest strength of 597.67 MPa, followed by the heat-affected zone of 549.42 MPa and base metal of 510.20 MPa, while the trend of elongation was opposite to that of strength. The microhardness distribution was not consistent with that of strength and had a maximum at the heat-affected zone.

Compressive responses of snap-fit Ti-6Al-4V octet-truss lattices in structure’s stiffest direction

A snap-fit method has been designed to establish octet-truss lattice for which the through-thickness direction coincides with structure’s stiffest (crystallographic) direction. Sheet Ti-6Al-4V alloy of a single thickness was used as the starting material for the assembly of lattices which were subsequently brazed in vacuum to bond the nodes. Ambient temperature uniaxial compressive responses of the manufactured lattices have been investigated quasi-statically as a function of the lattice relative density, and are shown to be consistent with micromechanics predictions and finite element simulations. Analytical study reveals anisotropic-shaped biaxial failure loci in principal stress space, which expand anisotropically with an increasing relative density, and demonstrate greater structural strengths under tensile-tensile and compressive-compressive loading states. An assessment of structural efficiency has shown that the present snap-fit route is superior to our previously reported methodology in acquiring mechanically robust lattice performance for applications where maximum rigidity of octet-truss structure is sought. The present work has relaxed the plausible assumption that truss-plane-orthogonality relation must be satisfied for a specific topology to realize its snap-fit construction; incremental types of topology are thus feasible for snap-fit production characterized by versatility in material selection, cost-effective, and scale-up production capability.

Fatigue behavior of REBCO coated conductors under through-thickness tensile stress

Fujikura Ltd has developed production techniques of REBa2Cu3O X (REBCO, RE = rare earth) coated conductors (CCs) using large-area ion-beam-assisted-deposition and hot-wall type pulsed-laser-deposition. We have provided high-performance REBCO CCs with long length and high homogeneity of critical current. The CCs are required to maintain their superconducting properties under mechanical stresses for a long-term. Therefore, it is important to evaluate the fatigue properties of the CCs. Although there are many investigations on cyclic tensile fatigue in the longitudinal direction of the CCs, few studies on fatigue properties in the through-thickness direction have been reported. In the case of the through-thickness stress, i.e. delamination stress, the stress is applied to the REBCO ceramic layer without substrate reinforcement, static fatigue fracture may occur by subcritical crack growth peculiar to ceramics. In this work, we carried out dynamic fatigue tests under delamination stresses at room temperature (RT) and liquid nitrogen (LN2) temperature 77 K to determine the fatigue coefficient N characterizing the static fatigue. As a result, we found that the N-value was relatively low (N ∼ 20) at RT, while the N-value was extremely high (N ∼ 150) at LN2 temperature. This result shows that the crack growth of the REBCO layer under the through-thickness tensile stress is extremely slow at low temperatures as well as that reported for bulk ceramics such as SiO2 glass. Therefore, it is expected that the static fatigue in the through-thickness direction of REBCO CC hardly occurs at low temperatures.