Lamination Direction Research Articles

A Study on the Damage Evolution Law of Layered Rocks Based on Ultrasonic Waves Considering Initial Damage

The damage evolution process of layered rock is influenced by its fine structure, lamination direction, and confining pressure, exhibiting significant anisotropic characteristics. This study focuses on shale as the research object, employing indoor tests and theoretical analysis to define damage variables and initial damage based on ultrasonic wave velocity. This research investigates the damage evolution law of layered rock under varying confining pressures and dip angles. The findings reveal that damage variables defined using transverse wave velocity effectively reflect the damage evolution process. Additionally, confining pressure significantly affects damage evolution, with increasing pressure causing a rightward shift in the damage variable–strain curve and an increase in initial damage. The slab inclination angle also influences damage evolution; samples with 45° and 60° inclinations are more susceptible to damage, with initial damage showing a trend of increasing and then decreasing. To accurately describe the relationship between damage variables and strain during the loading process, this paper establishes a segmented damage evolution equation characterized by wave velocity. Initially, an inverse proportional function is employed to characterize the strain before crack closure. Subsequently, a logistic function represents the curve from crack strain to peak strain. This combined approach provides a comprehensive depiction of the damage evolution. This study underscores the importance of considering confining pressure and laminar inclination in the analysis of rock stability and integrity. These results provide critical insights into the damage evolution characteristics of layered rocks, offering valuable references for engineering safety assessments.

Effects of interfacial debonding on the stability of finitely strained periodic microstructured elastic composites.

Predicting failure initiation in nonlinear composite materials, often referred to as metamaterials, is a fundamental challenge in nonlinear solid mechanics. Microstructural failure mechanisms encompass fracture, decohesion, cavitation, compression-induced contact and instabilities, affecting their unconventional static and dynamic performances. To fully take advantage of these materials, especially in extreme applications, it is imperative to predict their nonlinear behaviour using reliable, accurate and computationally efficient numerical methodologies. This study presents an innovative nonlinear homogenization-based theoretical framework for characterizing the failure behaviour of periodic reinforced hyperelastic composites induced by reinforcement/matrix decohesion and interaction between contact mechanisms and microscopic instabilities. Debonding and unilateral contact between different phases are incorporated by employing an enhanced cohesive/contact model, which features a special nonlinear interface constitutive law and an accurate contact formulation within the context of finite strain continuum mechanics. The theoretical formulation is demonstrated using periodically layered composites subjected to macroscopic compressive loading conditions along the lamination direction. Numerical results illustrate the ways in which debonding phenomena, in conjunction with fibre microbuckling, may influence the critical loads of the examined composite solid. The sensitivity of the results obtained through the proposed contact-cohesive model at finite strain with respect to its implementation is also explored. This article is part of the theme issue 'Current developments in elastic and acoustic metamaterials science (Part 1)'.

Residual strength and failure mechanism of CF/PPS composites with delamination damage

AbstractDelamination is one form of damage in composite laminates. The effects of delamination damage locations (thickness direction of laminates) on the residual compressive strength and failure mechanism of carbon fiber/polyphenylene sulfide (CF/PPS) composites are studied by damage morphology, full‐field strain and finite element simulation. The closer the delamination is to the center of the composite, the lower the residual compressive strength. The failure mode of composites is dominated by 0° fiber fracture, which is divided into bulging, delamination propagation, and fracture. The delamination locations significantly affect the first two stages.Highlights Constructing delamination damage in composites by interlayer preset defects. Simulation and damage analysis to reveal the mechanism of compression failure. The relationship between delamination depth and damage stage is revealed.

Structural and Mechanical Properties of Hot Rolled CuAlBe Non-Spark Alloy Explosion

Explosion protection is of particular importance for safety as explosions also endanger the health of workers due to the uncontrolled effects of flames and pressure, the presence of harmful reaction products and the consumption of oxygen in the ambient air breathed by workers. CuAlBe alloy is proposed as a solution for mechanical actuators such as gears that work in environments with possible explosive atmosphere. Made of CuBe master alloy and pure aluminum in a induction furnace the material present large grains in melted state. After the hot rolling (heated 600s at 900°C) of the ingots small variation of chemical composition was observed based on the oxidation of the material, appearance of small cracks on the edges and a preferential orientation of the grains along the lamination direction. Scanning electron microscopy (SEM) was used to characterize the microstructural states of CuAlBe as laminated and heat treated states.

Design of dissimilar material joint for defect-free multi-material additive manufacturing via laser-directed energy deposition

Additive manufacturing technology has advanced beyond creating optimized features, from strengthening materials to make them lightweight to fabricating multi-material combinations that offer functionalities beyond the capabilities of individual materials. In this study, a lamination method for laser-directed energy deposition (LDED) is developed to achieve dense multi-material features, and a design that combines different and dissimilar materials is developed. To evaluate these novel developments, two materials—AISI 316L stainless steel and Inconel 625—are introduced. Tensile specimens, fabricated via multi-material additive manufacturing using LDED, are subjected to tensile tests that are recorded on video for digital image correlation. After the tests, fracture surface analyses of the fractured specimens are performed via scanning electron microscopy, and optical monitoring analyses are performed on the specimens that are not subjected to the tensile tests. The results indicate that the specimens demonstrate varied mechanical properties due to the influence of lamination direction and order, which affect the formation of critical cracks and pores.

Analytical Assessment of Composite L Angle Strength Under Internal Fuel Pressure in Composite Wing

The Interspar (IS) box stores the turbine fuel in the composite wing of an Aircraft. The filled fuel is under pressure that induces out-of-plane stresses on all the wing’s structural members around the fuel tank’s boundary. The wing is designed using carbon fiber reinforced plastic (CFRP) with the co-curing of the bottom skin and its stringers along with front and rear spars. A suitable number of cut-outs are made on the top and bottom sides of the IS ribs for the stringer to pass through them. The global finite element analysis showed that the stringer cut-out regions in the IS ribs are highly stressed, as they are subjected to out-of-plane load due to internal fuel pressure, which induces transverse tensile stress in the cut-out region. Resin is the weakest material in the composite laminate, but it has to resist the high-stress component due to out-of-plane loads. The top and bottom flanges of the ‘C’ section IS ribs geometrically form an L angle section with a stringer cut-out made in it. At the L angle location, the IS ribs are critical from both the strength and stiffness point of view. Strength and stiffness at the interface of the fastener joint are essential factors in maintaining the composite wing’s overall structural integrity under internal fuel pressure. The authors adopted the same standalone finite element (FE) modelling approach developed for the Bond Energy Method and carried out appropriate analytical studies to ascertain the safety and structural integrity of the composite wing under internal fuel pressure. This article presents the analytical study carried out on the standalone FE model of an L angle with the stringer cut-out introduced at its appropriate position. The static stress analysis is carried out by enforcing the global displacement on this standalone FE model and extracting three force components in CBAR beam elements representing the resin property in the transverse direction of the composite laminate. The stresses are calculated outside the analysis deck using Excel® spreadsheets. The maximum Normal Stress (σn) in the L angle flange is found to be 13.25 MPa, which is well within the resin or transverse tensile strength of the composite laminate 53 MPa, and the shear stress is found to be 11.10 MPa, which is less than the resin shear strength property of 23 MPa. Hence the study showed that the L angle is safe for carrying internal fuel pressure of 12.5 PSI. The study also showed that the strain and displacement values distribution in the standalone FE model are comparable with that of the global wing box model within the range of (8-10) % and (4-5) % difference, respectively.

Surface-Wetting Characteristics of DLP-Based 3D Printing Outcomes under Various Printing Conditions for Microfluidic Device Fabrication.

In recent times, the utilization of three-dimensional (3D) printing technology, particularly a variant using digital light processing (DLP), has gained increasing fascination in the realm of microfluidic research because it has proven advantageous and expedient for constructing microscale 3D structures. The surface wetting characteristics (e.g., contact angle and contact angle hysteresis) of 3D-printed microstructures are crucial factors influencing the operational effectiveness of 3D-printed microfluidic devices. Therefore, this study systematically examines the surface wetting characteristics of DLP-based 3D printing objects, focusing on various printing conditions such as lamination (or layer) thickness and direction. We preferentially examine the impact of lamination thickness on the surface roughness of 3D-printed structures through a quantitative assessment using a confocal laser scanning microscope. The influence of lamination thicknesses and lamination direction on the contact angle and contact angle hysteresis of both aqueous and oil droplets on the surfaces of 3D-printed outputs is then quantified. Finally, the performance of a DLP 3D-printed microfluidic device under various printing conditions is assessed. Current research indicates a connection between printing parameters, surface roughness, wetting properties, and capillary movement in 3D-printed microchannels. This correlation will greatly aid in the progress of microfluidic devices produced using DLP-based 3D printing technology.

Investigations on the thermo-mechanical behaviour of densified veneer wood for cryogenic applications

ABSTRACT In this study, the thermo-mechanical behaviour of densified veneer wood (DVW) for cryogenic applications like load-bearing insulation elements for liquid energy sources is investigated. Mechanical tests with compression parallel and transverse to the veneer plane were performed after conditioning the material at five temperature levels: +60°C, +20°C, −40°C, −78°C (dry ice) and −196°C (liquid nitrogen). The investigations showed increasing compression moduli but also increasing brittleness with decreasing temperature. The compressive strength increased with decreasing temperature until about −30°C. Below this temperature, the strength slightly decreased again. The specific heat capacity was determined in the range of −150°C to +60°C and showed a linear dependency on temperature below +20°C. Above +20°C, a non-linear increase is observed due to evaporation of bound water. Finally, a technique is presented to mould DVW boards transverse to the lamination direction with a thermo-hygro-mechanical process in order to reduce waste material associated with commonly used chipping techniques.

Collaborative optimization for variable stiffness composite laminates using a fiber angle description method based on Archimedean spiral function

When optimizing the fiber orientation of multilayer composite laminates, with the increasing number of layers, the number of design variables increases sharply, resulting in a large amount of computational cost. To address this challenge, this paper proposes a novel discrete fiber angle optimization method based on the Archimedean spiral function and applies it to a collaborative design framework of topology and fiber orientation. The proposed method uses the normal distribution function as the angle selection function in every layer. To prevent convergence issues in optimizing the fiber angle, a new candidate angle weighting formula is proposed. Further, a discrete fiber angle parameterization method based on the Archimedean spiral function for the thickness direction of laminates is presented, which requires only one variable to represent the fiber angle of any two layers in the element. To circumvent the issue of local optima and expand the design space, a collaborative optimization strategy is employed to improve the discrete fiber angle optimization results. Finally, the numerical examples indicate that in comparison to conventional approaches, the correlation of the proposed method with initial values is significantly reduced (σ2=0.00188). Under identical initial conditions, this method can improve the structural stiffness by over 20% at maximum.

Hierarchical 3D Porous Hydrogen-Substituted Graphdiyne for High-Performance Electrochemical Lithium-Ion Storage.

Graphdiyne (GDY) has realized significant achievements in lithium-ion batteries (LIBs) because of its unique π-conjugated skeleton with sp- and sp2-hybridized carbon atoms. Enriching the accessible surface areas and diffusion pathways of Li ions can realize more storage sites and rapid transport dynamics. Herein, three-dimensional porous hydrogen-substituted GDY (HsGDY) is developed for high-performance Li-ion storage. HsGDY, fabricated via a versatile interface-assisted synthesis strategy, exhibits a large specific surface area (667.9 m2 g-1), a hierarchical porous structure, and an expanded interlayer space, which accelerate Li-ion accessibility and lithiation/delithiation. Owing to this high π-conjugated, conductive, and porous framework, HsGDY exhibits a large reversible capacity (930 mA h g-1 after 100 cycles at 1 A g-1), superior cycle (720 mA h g-1 after 300 cycles at 1 A g-1), and rate (490 mA h g-1 at 5 A g-1) performances. Density functional theory calculations of the low diffusion barrier in the lamination and vertical directions further reveal the fast Li-ion transport kinetics of HsGDY. Additionally, a LiCoO2-HsGDY full cell is constructed, which exhibits a good practical charge/discharge capacity of 128 mA h g-1 and stable cycling behavior. This study highlights the advanced design of next-generation LIBs to sustainably develop the new energy industry.

An investigation on ultrasonic wave velocity of laminated sandstone under freeze-thaw and salt crystallization cycles: Insights from anisotropy effects

In this study, the anisotropy effects on the P (Vp) and S (Vs) wave velocities are investigated in laminated sandstone subjected to freeze-thaw (FT) and salt crystallization (SC) processes. For this purpose, cylindrical core specimens were prepared from sandstone at angles (β) of 0°, 30°, 45°, 60°, and 90° to the lamination direction. Next, FT and SC tests were performed up to 60 cycles. After every 10 cycles, the specimens’ Vp and Vs were determined at various β values. The decay constant (λ), half-life (N1/2), and rate of loss (RL) were used to investigate the anisotropy effects on the Vp and Vs of specimens under FT and SC and compare the effects of FT and SC on the Vp and Vs. The results indicated that anisotropy is an important factor in the durability of the specimens against FT and SC. In this respect, the specimens with β = 0° and β = 60° had the least and the highest changes in the Vp and Vs, respectively. Also, it was found that the anisotropic behavior of the specimens is different at various cycles of FT and SC such that it is intensified at higher cycles. Overall, it was concluded that SC had more significant effects on the Vp and Vs compared to FT. Considering the β values, the effect of a single cycle of the SC test in decreasing the Vp and Vs of the specimens corresponds to 1.34 to 1.94 and 1.28 to 1.70 cycles of the FT test, respectively.

A deep learning approach to inverse scattering analyses: Recovering interfacial defects in laminated structures

We propose a deep learning (DL) regression strategy to solve inverse acoustic scattering problems. This strategy is capable of recovering heterogeneous defect fields in any interface and direction of composite laminates. The training procedure of the neural network (NN) model uses stochastic Gaussian fields as output, which are related to interfacial damage fields of the physical problem. We assume prior knowledge of the material properties of the ultrasound incident field and the elastic layers’ properties. Furthermore, we model the interfaces using the Quasi-Static-Approximation, a method that generates position-dependent interfacial stiffness matrices, composed of a set of uncoupled normal and tangential springs. We validate our approach and evaluate its performance for noisy input data and reduced-order models. Additionally, we also consider model errors at the composite interfaces. The obtained results show that the presented method is promising due to its generalization capability in recovering different defect field profiles, its robustness in relation to noisy data and model errors and its low computational cost, once the DL model is trained, in comparison to traditional inverse approaches (iterative).

The investigation on dynamic damage evolution and energy absorption of FML pin joints with different ply stacking sequences

With fiber reinforced composites widely applied in aerospace, the crashworthiness aspects for aircraft have been an important part of the design. Fiber metal laminate (FML) is a kind of hybrid composite fabricated by fiber reinforced plastic composites and metal layers, showing a potential application on energy absorption. In this work, the damage evolution and energy absorption of FML pin joints are investigated comprehensively. The configurations of FML pin joints with constant geometric parameters are designed to avoid net-tension damage failure in the experiments. The damage evolution processes of specimens are captured by a high-speed camera, and the surface strain is calculated by Digital Image Correlation (DIC) method. Abaqus/Explicit solver is adopted to simulate the mechanical responses of FML pin joint considering ductile damage of metal, damage evolution of composites, and delamination of the interface. The results indicate that the initial dynamic ultimate bearing strength of FML incorporate notable contribution from inertia effects. The average bearing strength associated with energy absorption efficiency is related to the ply stacking sequence of composites. The fiber direction of laminates should be perpendicular to the movement direction of pin as much as possible under the premise that the initial ultimate bearing strength satisfies the design requirement. The results obtained in this work provide comprehensive design guidance for the improvement of crashworthiness in the composite fuselage.

On the Possibility of Using 3D Printed Polymer Models for Modal Tests on Shaking Tables: Linking Material Properties Investigations, Field Experiments, Shaking Table Tests, and FEM Modeling

In this article, the possibility and the pertinence of using 3D printed polymeric materials for models in modal tests on shaking tables were recognized. Four stages of the research have been linked: The material properties investigation, the field experiment on the modal properties of the reinforced concrete chimney (a prototype), the shaking table tests on the modal properties of the 3D printed polymer model of the chimney, scaled according to the similarity criteria, and the numerical calculations of the FE model of the 3D printed mockup. First, the investigation of the properties of 3D printed polymer materials revealed that the direction of lamination had no significant effect on the modulus of elasticity of the material. This is a great benefit, especially when printing models of tall structures, such as chimneys, which for technical reasons could only be printed in a spiral manner with the horizontal direction of lamination. The investigation also proved that the yield strength depended on the direction of the lamination of the specimens. Next, the natural frequencies of the chimney, assessed through the field experiment and the shaking table tests were compared and showed good compatibility. This is a substantial argument demonstrating the pertinence of using 3D printed polymer materials to create models for shaking table tests. Finally, the finite element model of the 3D printed polymer mockup was completed. Modal properties obtained numerically and obtained from the shaking table test also indicated good agreement. The presented study may be supportive in answering the question of whether traditional models (made of the same material as prototypes) used in shaking table tests are still the best solution, or whether innovative 3D printed polymer models can be a better choice, in regard to the assessment of the modal properties and the dynamic performance of structures.

Research on 3D Printing Technology of Polylactic Acid

Additive manufacturing technology(3D printing) as a rapid development of rapid prototyping technology in recent years. However, the surface quality and mechanical properties of the molded parts are worse than those of traditional material reduction manufacturing due to the special bottom-up processing and forming principle. In this paper, the performance of FDM parts is improved by studying the process parameters. According to the actual research situation, this paper selected the filling density, printing speed, printing temperature, stratification direction for experimental research. Through orthogonal test and single factor method, the best strength combination is obtained as filling density 80%, printing speed 35mm/s, printing temperature 195℃. After range analysis, it is found that the filling density has the greatest influence on tensile strength, followed by printing speed and printing temperature. the lamination direction also has a significant influence on tensile strength.

Mode I fracture behavior of unidirectional bamboo laminate and its applications to the estimation of bamboo-steel-bamboo connections’ bearing capacities

Fracture caused by crack propagation is prevalent in bamboo laminate. Mode I fracture of bamboo laminate in which the fracture surface is composed of multilayer strips with fracture along the Tangential-Longitudinal (T-L) direction was studied. The load-crack opening mouth displacement (CMOD) curves of Mode I fracture, and the post-peak behavior of bamboo laminate were analyzed. The Mode I fracture toughness was calculated based on the modified beam theory. The effect of the bamboo node on fracture toughness was studied. The Mode I fracture toughness of bamboo laminate increases with the crack growth due to bamboo nodes. The toughening mechanism is the interlocking effect and fiber bridging on the uneven fracture surface. The mean value of the Mode I fracture toughness of unidirectional bamboo laminate panels along the y-x direction of the unidirectional bamboo laminate was suggested to be 225.7 J/m2 for the estimation of bamboo-steel-bamboo connections' bearing capacities. Based on the measured fracture properties of bamboo laminate and the fracture mechanics models, the brittle bearing capacities of the bamboo-steel-bamboo connections were discussed at the end of this research.

Numerical investigation on behaviors of composite laminates with initial delamination defects under impact and compression after impact

AbstractThe initial delamination defects may arise during the preparation of carbon fiber‐reinforced polymer (CFRP) composite laminates, so its effects need to be considered in the evolution of mechanical properties. In this article, the behaviors of composite laminates with initial delamination defects under impact and compression after impact (CAI) are investigated by numerical method. The simulation framework composed of the micromechanics of failure (MMF) theory and the mixed mode exponential cohesive zone model (ECZM) is constructed. The numerical analysis compares the effects of the interaction between four different initial delamination defects and impact loading on impact response and CAI strength at two impact velocity levels (1.336 and 2.314 m/s). Furthermore, the failure mechanisms of laminates with initial delamination defect are disclosed under CAI loading. The findings indicate that the difference in impact response is minor. The CAI strength is reduced from 250.5/173.5 to 191.5 MPa/139.1 MPa. The sufficient condition for the further significant reduction of CAI strength is that the initial delamination defects merge with the impact‐induced delamination cracks in the width direction of laminates. Moreover, the failure mechanism for CAI condition is mostly matrix damage and interlaminar crack propagation. This work provides a valuable reference for engineering failure analysis of composite laminates.

Statistical fatigue failure life of unidirectional CFRP under bending load

Our developed accelerated testing methodology (ATM) based on the matrix resin viscoelasticity for the failure life prediction of carbon-fiber reinforced polymers (CFRP) was applied for statistical prediction of long-term fatigue failure life under bending load for the longitudinal direction of unidirectional CFRP laminates, which is an important basic aspect of design for the durability of CFRP structures used for aircraft and other applications. First, the formulations for fatigue life prediction of FRP under cyclic loading are introduced. Second, the time-dependent and temperature-dependent viscoelasticity of matrix resin and the statistical flexural static strengths of CFRP laminates at various temperatures are introduced as the basic data of failure life prediction of CFRP laminates. Third, fatigue bending tests for CFRP laminates are performed at various load levels with various frequencies and temperatures. A master curve of non-dimensional fatigue strength versus number of cycles to failure (S-N master curve) is constructed by substituting data of the second and third steps into the formulations. Finally, the long-term fatigue strength data obtained under cyclic bending load for unidirectional CFRP laminates are compared with the long-term creep strength obtained in the previous paper.

A criterion for predicting delamination growth in composite laminates

To develop a simplified and physically sound delamination-failure criterion, this paper reports a joint experimental and numerical study in which out-of-plane quasi-static indentations with different indentation forces were applied to the centre of fully clamped rectangular carbon fibre-reinforced polymer (CFRP) laminates. The results show that two basic micro-delamination growth modes, which are separately dominated by opening and sliding microcracks, can be distinguished according to the fracture morphologies of the delaminations along the 0° fibre direction. Both are driven by the out-of-plane shear stress σ13, and the corresponding delamination failure threshold is the out-of-plane shear strength S13. Based on these results, a concise Hashin-type delamination-propagation criterion containing only a single stress component and single strength parameter is proposed, which, by incorporating it into the finite element model, the delamination growth along the fibre directions of multidirectional CFRP laminates can be precisely predicted; the prediction error is less than 10 %.

Assessment of Cryogenic Material Properties of R-PUF Used in the CCS of an LNG Carrier

Reinforced polyurethane foam (R-PUF), a material for liquefied natural gas cargo containment systems, is expected to have different mechanical properties depending on its stacking position of foaming as the glass fiber reinforcement of R-PUF sinks inside R-PUF under the influence of gravity. In addition, since R-PUF is not a homogeneous material, it is also expected that the coordinate direction within this material has a great correlation with the mechanical properties. So, this study was conducted to confirm this correlation with the one between the mechanical properties and the stacking position. In particular, in this study, R-PUF of 3 different densities (130, 170, and 210 kg/m3) was used, and tensile, compression, and shear tests of this material were performed under 5 temperatures. As a result of the tests, it was confirmed that the strength and modulus of elasticity of the material increased as the temperature decreased. Specifically, the strength and modulus of elasticity in the Z direction, which was the lamination direction, tended to be lower than those in the other directions. Finally, the strength and elastic modulus of different specimens of the material found at the bottom of their lamination compared to the specimens with these properties found at positions other than their lamination bottom were evaluated. Further analysis confirmed that as the temperature decreased, hardening of R-PUF occurred, indicating that the strength and modulus of elasticity increased. On the other hand, as the density of R-PUF increased, a sharp increase in strength and elastic modulus of R-PUF was observed.