Laminate Structure Research Articles

Exploring the coupled effects of interfaces and grain size gradients in heterogeneous laminate and gradient structures via a multiple mechanism based constitutive model

Abstract As two promising types of heterogeneous materials, gradient structures and heterogeneous laminates possess superior mechanical properties, such as a combination of high strength and exceptional ductility, which can be attributed to back stress strengthening and strain hardening arising from their heterogeneous microstructures. Recent efforts have been made to combine these two unique microstructures to further improve their properties and performance. However, how heterogeneous interfaces and grain size gradients interplay with each other remains unknown. Therefore, this work aims at exploring the coupled effects of interfaces and grain size gradients in copper–bronze heterogeneous laminate and gradient samples via multiple mechanism-based constitutive modeling incorporating statistically stored dislocations, geometrically necessary dislocations, back stress and deformation twinning. It is revealed that different grain size gradients have profound influence on the deformation mechanisms and mechanical behaviors of the material: a monotonic grain size gradient in the copper layers strengthens the material yet reduces its ductility as a result of diminished back stress hardening due to weakened interface effects; a symmetric grain size gradient in the bronze layers leads to an increase in ductility and a decrease in strength; only by introducing a symmetric grain size gradient into the copper layers can the strength and ductility of the material be improved simultaneously, which is accredited to stronger back stress and grain boundary strengthening due to the synergistic effects between the interfaces and the grain size gradients. In addition, the distinct propensities for twinning in the copper and bronze layers can be attributed to both their different stacking fault energies and grain sizes.

Characteristics of Lamination in Deep Marine Shale and Its Influence on Mechanical Properties: A Case Study on the Wufeng-Longmaxi Formation in Sichuan Basin

The extensive development of lamination structures in shale significantly influences its mechanical properties. However, a systematic analysis of how laminae affect the macroscopic mechanical behavior of rocks remains absent. In this study, field emission scanning electron microscopy (FE-SEM), thin section observation, X-ray diffraction (XRD), triaxial compression and Brazilian tests were carried out on the deep marine shale of the Wufeng-Longmaxi Formation in Sichuan Basin. The results reveal four distinct laminasets: grading thin silt–thick mud (GSM1), grading medium thick silt–mud (GSM2), grading thick silt–thin mud (GSM3) and alternating thick silt–thin mud (ASM). GSM3 and ASM laminasets exhibit the weakest mechanical properties and the simplest fracture patterns, while GSM2 demonstrates moderate mechanical properties and more complex fracture patterns. GSM1 shows the highest mechanical strength and the most intricate fracture patterns. Mechanical properties are positively correlated with siliceous mineral content and negatively correlated with clay mineral content and scale of laminae development (average density and thickness), revealing that lamination plays a key role in fracture behavior, with more intensively developed laminasets leading to the concentrated distribution of brittle silty minerals, facilitating microcrack propagation. Moreover, microstructure has an important effect on both mechanical properties and fracture pattern. In grain-supported structures, closely packed silty brittle mineral grains reduce the energy required for crack extension. In matrix-supported structures, widespread silty brittle mineral grains increase energy requirements for crack extension, leading to more irregular and complex fracture networks. This study enhances the understanding of the effects of lamination on the rock mechanical behavior of shales, optimizing hydraulic fracturing design in shale reservoirs.

Input-optimized physics-informed neural networks for wave propagation problems in laminated structures

Accurate prediction of wave propagation characteristics in laminated structures is crucial for engineering applications, such as ultrasonic examination and composite material optimization. This study develops a novel framework based on extended physics-informed neural networks (XPINNs) to enable the analysis and prediction of wave propagation in laminated structures. The XPINNs with domain decomposition are extended to model multilayered laminated structures, with each sub-PINN governing an individual component layer. An innovative hybrid-handed coordinate system is proposed to address compatibility conditions among layers and unify all inputs of sub-PINNs, developing an input-optimized framework named unified-input XPINNs (Uni-XPINNs). Three types of errors, including the relative root mean square error, the relative absolute error, and the mean square error, are utilized to assess the performance of the proposed framework against analytical solutions and finite element simulations. Based on the obtained prediction models, the study investigates the impact of body forces on wave propagations in laminated structures. Numerical results demonstrate high accuracy in predicting wave propagation in laminate structures, with a maximum error of 3.063% for all cases discussed. It is observed that body forces significantly affect wave propagation when they exceed a specific threshold. Below this threshold, their impacts are minimal. This research explores the application of machine learning methods to solve wave propagation problems, offering alternatives to traditional theoretical methods and numerical simulations.

Quality prediction and process optimization in abrasive waterjet cutting of ultra‐thick carbon fiber reinforced polymer

AbstractSurface roughness and delamination extent are key indicators for assessing the surface quality of machined carbon fiber reinforced polymer (CFRP) laminates. This study conducted an in‐depth investigation on the uncontrollable surface quality of abrasive water jet (AWJ) machining of ultra‐thick CFRP. Considering the sensitivity of the laminate structure to the jet impact angle, an optimized response surface methodology was used to analyze the effects of process parameters on surface roughness. Additionally, the differences in surface roughness on both sides of the kerf under non‐orthogonal cutting were examined. Based on these analyses, a surface roughness prediction model was developed. Furthermore, the study comprehensively analyzed the effects of material mechanical properties and process parameters on delamination damage. Using dimensional analysis, a predictive model for the maximum delamination length, considering jet energy dissipation, was established. The novelty of this research is to reveal the difference in surface quality on both sides of the kerf under non‐orthogonal cutting, and to establish prediction models for surface roughness and delamination damage based on the energy dissipation characteristics of ultra‐thick CFRP AWJ machining. This research provides essential modeling foundations for enhancing the controllability of AWJ machining quality for ultra‐thick CFRP complex components.Highlights Surface roughness and delamination damage impact AWJ use for ultra‐thick CFRP. Non‐orthogonal cutting causes surface quality differences on kerf sides. A model for kerf surface roughness at any jet impact angle was established. The delamination mechanism in internal path cutting was analyzed. The delamination length model for ultra‐thick CFRP laminates was established.

Analysis of Tensile Failure Behavior of Metal Fiber Laminates Under Different Temperature Environments.

The tensile properties of fiber metal laminates were examined at temperatures ranging from 30 °C to 180 °C in this paper through the integration of numerical simulation techniques, experimental measurements, and digital image correlation techniques. The laminates were initially modeled using finite elements, and the failure behavior of porous basalt-fiber-reinforced aluminum alloy plates was numerically simulated. Consequently, metal fiber laminate stress-strain responses were varied by numerous tensile experiments conducted at varying temperatures. Simultaneously, a scanning electron microscope was used to scan a porous basalt-fiber-reinforced aluminum alloy laminate at different temperatures to determine the tensile mechanical behavior and micro-damage morphology. Lastly, the laminate's dynamic response to the tensile process was observed through digital image correlation technology. The stress distribution was determined to be concentrated around circular openings through analysis. The strain distribution graph exhibited a "band" shape as the number of perforations increased. The findings indicate that fiber metal laminates lose tensile strength as temperatures increase. The ultimate tensile strength of the laminate decreases as the number of perforations increases at the same temperature. Complex damage mechanisms, including matrix debonding, fiber withdrawal, and matrix fracture, can be captured through scanning electron microscopy at varying temperatures. The tensile behavior and damage mechanisms of laminates with hole-containing structures under thermal conditions are examined, and the results can be used to inform the design and utilization of laminate structures.

Evolutionary topology optimization with stress control for composite laminates using Tsai-Wu criterion

In this study, a topology optimization technique with stress control is proposed for the composite laminates. The bi-directional evolutionary structural optimization (BESO) method is selected to avoid the stress singularity. The technique expresses the failure index based on the Tsai-Wu criterion, thereby ensuring a comprehensive consideration of the anisotropy. To address the local nature of stress and multi-layer structure of laminates, a nested p-norm is employed, providing a global approximation of the local maximum failure index. To mitigate the highly non-linear stress behaviors, filter schemes are applied to both sensitivity numbers and design variables. Sensitivity numbers are derived via adjoint sensitivity analysis and Lagrange multipliers to address stress-based and stress-constrained problems. The proposed framework is validated through systematic numerical studies across various examples and conditions, offering insights into the topological behaviors of composite laminates. This study underscores the importance of considering distinct tensile and compressive strength in composite materials, which represents a key innovation. Additionally, the relationships among stiffness-based, stress-constrained, and stress-based designs are explored in depth.

Experimental study of the couple effects of internal and external cooling on double-wall laminate structure with novel slot and pin-fins

This study investigates the couple effects of internal and external cooling on double-wall laminate cooling (DWLC) structure with novel impingement jet, pin-fins, and slot hole. The distribution of film cooling effectiveness (FCE) and heat transfer coefficient (HTC) were measured using transient liquid crystal (TLC) and pressure sensitive paint (PSP) methods. In order to improve the accuracy of TLC method, a thermal inertia correction method based on radial basis function neural network (RBFNN) was proposed. It was found that the pin-fins would significantly affect the external film cooling characteristics. There is a counter-rotating vortex pair at the downstream of the pin-fins inside the coolant film. This leads to a higher FCE at the downstream region of pin-fins and a lower FCE at the region between the pin-fins. The internal heat transfer is minimally influenced by slot height and inclination angle. Increasing filling ratio greatly reduces the area-averaged FCE and changes the flow field at slot outlet. The DWLC structure in this study shows excellent cooling performance and is currently mainly used in the field of aero-engines. However, it can also be applied to the cooling design of gas turbines, electronics, and other fields after scaling the size. Additionally, the improved TLC experimental method can be widely used in heat transfer measurement in the aforementioned research fields.

Strong and Stable Woody Triboelectric Materials Enabled by Biphase Blocking.

Driven by the "Internet of Everything" (IoE) vision, the demand for smart materials is growing. Wood, one of the most abundant and renewable resources, has long been a staple in construction and furnishing applications. To further expand its application range, this study developed a high-strength, stable wood-based triboelectric material through a synergistic biphasic mechanism. The in situ growth of flame retardants and the formation of a dense char layer significantly enhanced the fire resistance of the wood-based triboelectric material, reducing the heat release rate (HRR) by 95.4% and total heat release (THR) by 94.2%. The dense laminate structure provided an excellent impact toughness (126 kJ m-2). As a smart sensor, the wood-based triboelectric material demonstrated the ability to recognize human motion states and trajectories, exhibiting great potential for applications in smart homes. This study provides valuable insights for exploring the potential applications of wood as a smart material.

Immobilization and coordination chemistry of Friedel’s salt (Ca/Al-LDHs) on heavy metals removal

Friedel’s salt (F’s salt, FS, Ca/Al-LDHs) was prepared via coprecipitation synthesis to remove Pb(II) and Zn(II). The adsorption of F’s salt on Pb(II) and Zn(II) was a physical adsorption process and could be well described by pseudo-second order kinetics. The adsorption process is mainly completed by surface adsorption of pore structure and interlayer structure. In addition, the crystal microstructure parameter, molecular structure and elemental spatial distribution analysis results demonstrated that Pb(II) and Zn(II) could form new solid solutions such as Pb/CaAl-Cl-LDHs, CaZn/Al-Cl-LDHs and Zn/CaAl-Cl-LDHs via lattice replacement, and then effectively immobilized in F’s salt crystals. Unlike Pb(II), there are two fixed lattice substitution pathways for Zn(II), that is, Ca(II) and Al(III) can be used as replacement objects. Notably, the chemical bonding mechanism is more prominent for the solidification of Pb(II) than that of Zn(II) in F’s salt. Moreover, the superficial coordination chemistry analysis results revealed that the abundant OH groups distributed in the main layer laminate structure can also serve as the binding sites for Pb(II) and Zn(II). This study provides a theoretical basis and novel insights into the immobilization mechanism of Pb(II) and Zn(II) in F’s salt.

Emerin preserves stem cell survival through maintenance of centrosome and nuclear lamina structure.

Drosophila female germline stem cells (GSCs) complete asymmetric mitosis in the presence of an intact, but permeable, nuclear envelope and nuclear lamina (NL). This asymmetric division requires a modified centrosome cycle, wherein mitotic centrosomes with mature pericentriolar material (PCM) embed in the NL and interphase centrosomes with reduced PCM leave the NL. This centrosome cycle requires Emerin, an NL protein required for GSC survival and germ cell differentiation. In emerin mutants, interphase GSC centrosomes retain excess PCM, remain embedded in the NL and nucleate microtubule asters at positions of NL distortion. Here, we investigate the contributions of abnormal interphase centrosomes to GSC loss. Remarkably, reducing interphase PCM in emerin mutants rescues GSC survival and partially restores germ cell differentiation. Direct tests of the effects of abnormal centrosomes were achieved by expression of constitutively active Polo kinase to drive enlargement of interphase centrosomes in wild-type GSCs. Notably, these conditions failed to alter NL structure or decrease GSC survival. However, coupling enlarged interphase centrosomes with nuclear distortion promoted GSC loss. These studies establish that Emerin maintains centrosome structure to preserve stem cell survival.

A unified method to generate representative volume elements with tailored random fibre arrangements to estimate the shear and transverse behaviours of unidirectional continuous fibres composite plies

Axial compressible strength is a key design parameter of CFRP laminate structures, especially for Aerospace where maximum flexure on wings is driven by the global margin of safety on compressive loads. One of its main limiting contributors is the non-linear shear behaviour of the unidirectional ply. This shear response can be predicted by using generated (quasi-)random microstructures set within representative volume elements (RVE). Different microstructures with or without clusters of fibres (resulting from manufacturing processes) are necessary to quantify the mechanical variability. The variability of the microstructures is characterised by the variation of the arrangement, the volume fraction and the misalignment of the fibres. This leads to significant variations in the mechanical performance, in particular for the shear behaviour. In this study, we propose a unified algorithm that makes it possible to generate all the different positions of fibres in microstructures with very high fibre volume fractions. The microstructural parameters responsible for variations in mechanical behaviour are identified to establish a correlation between fibre distribution and the mechanical response. Finally, a composite cross-section is analysed to estimate the local non-linear shear behaviour as well as the compressive strength as an example to illustrate the benefit of complex microstructures modelling.

Dual magnetoelectric antenna array with enhanced bandwidth and sensitivity for low-frequency communications

The magnetoelectric coupling effect demonstrated immense potential for miniaturizing antenna applications. However, due to the resonant nature of magnetoelectric (ME) antennas, their bandwidth tended to be relatively narrow. To address this limitation, our study introduced an array design based on coupled ME antennas. A tri-layer FeGa–PZT8–FeGa laminate structure was employed to construct the ME antennas, which utilized inter-array coupling to broaden the frequency range. Both the central frequency and sensitivity of the array structure were theoretically analyzed, and two methods for extending the frequency were proposed. By coupling two ME antennas of similar frequency in the series mode, the arrayed ME antennas exhibited enhanced sensitivity, increasing from 0.225 and 0.247 to 0.413 mV/nT, and an expanded bandwidth from 0.92–1.03 to 1.4 kHz, indicating improved performance through combined configuration. On the other hand, by coupling two ME antennas of different frequencies together in the series mode, a dual-frequency (97.8/98.97 kHz) ME antenna array was formed. The communication capabilities of the ME antenna array under weak magnetic fields were demonstrated using amplitude shift keying and frequency shift keying modulation methods. The designed array of ME antennas elevated low-frequency communication performance and possessed excellent magnetic field detection capabilities, thereby offering a cost-effective technological pathway for bioelectronic and marine communication design.

A one-step integrated forming and curing process for smart thin-walled fiber metal laminate structures with self-sensing functions

This study proposes and analyzes a novel one-step integrated forming and curing (IFC) process for thin-walled fiber metal laminates (FMLs) structures embedded with fiber Bragg grating (FBG) sensors, and have achieved both high-performance properties and self-sensing functions in the formed structures. A prototype machine and testing setup have been developed to validate the process's feasibility by manufacturing high-performance FMLs flat and curvature parts with effective self-sensing capabilities for real-time manufacturing and in-service monitoring. Numerical models considering curing-induced deformation and heat transfer during manufacturing have also been developed to support the analysis and validation of the self-monitoring capabilities of the intelligent FMLs parts. The results reveal that with proper control of pressure (e.g., 0.6 MPa) and time during forming and curing, high tensile and impact performance of FMLs can be maintained with embedded FBG, with less than a 3 % loss. Additionally, the IFC process can effectively lead to an apparent reduction of springback deformation in the formed FMLs (more than 80 %). The validation of the self-sensing function during the manufacturing process has been achieved by comparing the strain monitoring results with finite element (FE) simulation results during curing, with a minimum discrepancy of 2.0 %. For the in-service self-sensing function, comparison between FE analysis and surface-fixed strain gauges during the compression instability test confirmed the efficacy of FBG sensors, with a minimum discrepancy of 4.3 %. The results show that the proposed novel IFC process enables the successful manufacture of smart thin-walled FMLs parts with high shape accuracy and mechanical properties in a single step and holds significant promise for manufacturing self-sensing smart structures in the aerospace and aviation industries.

Quantitative analysis of the impact of wrinkle defects on the strength of wind turbine blade main spars

Abstract Understanding the impact of wrinkle defects on the main spar of wind turbine blades is crucial for maintaining structural integrity and ensuring operational efficiency. This paper focuses on a quantitative analysis to determine how varying severities of wrinkles affect the structural strength of wind turbine blades. First, the study employed infrared nondestructive testing technology to inspect in-service wind turbine blades, identifying wrinkle characteristics. Based on these detected characteristics, finite element models were established to simulate the structural behavior. The Hashin failure criterion was employed to forecast the initiation of intralaminar damage, while a cohesive model with a bilinear traction-separation criterion was used to evaluate the interlaminar stress state and damage behavior of the laminates. Last, to achieve accurate simulation, a VUMAT subroutine was developed and executed in the ABAQUS software environment. The simulation results for ultimate tensile strength at different ratios of amplitude to wavelength were found to be within 10% of the experimental values. This level of accuracy underscores the reliability of the models used. The study revealed that as the ratio of amplitude to wavelength increases from 0.4 to 0.69, the ultimate tensile strength of the laminate structure decreases to one-fourth of its original value. This significant reduction highlights the severe impact that wrinkle defects can have on structural performance.

Numerical and experimental frequency analysis of damaged fiber‐reinforced metal laminated composite

AbstractThis research numerically evaluated the eigenvalue responses of the damaged fiber metal laminate (FML) structure. The current numerical model is delved into including crack‐type damage effect on the structural integrity/ stiffness via frequency response. In this regard, a complete mathematical model of FML has been derived through higher‐order shear deformation kinematics for computational purposes. The mathematical model is converted to computer code in the MATLAB platform to predict the eigenvalue responses of FML components with and without damage. The damage influences are considered via circular meshing of finite element steps associated with the isoparametric element (nine nodes and nine degrees of freedom for each node). The solution consistency is checked via convergence, and the results are compared with data available in the open domain. Further, an experimental test is carried out to improve confidence using an in‐house test rig. The experiment was conducted by varying the length of the FML in 0.1 m increments. The results showed good agreement between the numerical and experimental data, with the lowest deviation being 0.29% and the highest 8.97%. The developed numerical model is extended to analyze the influences of design parameters such as geometry shape, aspect ratio (a/b), thickness ratio (a/h) ratio, curvature ratio, and fiber layup sequence on the natural frequency response.

Investigations of three-dimensional fiber orientation on mechanical impact behavior of short glass-fiber-reinforced PEEK composites

This work presents experimental and numerical investigations of three-dimensional (3D) fiber orientation on mechanical impact behavior of short glass-fiber-reinforced polyether ether ketone (SGFR PEEK) composites. The incorporation of short fibers significantly enhances the stiffness and strength of the composites while reducing the ductility, thereby, making the study of their impact response essential. To this end, we firstly manufactured the composite components using injection molding, and used the micro-computed tomography (µCT) to measure the fiber orientation distribution in 3D space for mechanical behavior prediction. Then, by studying the molded components across the thickness based on the actual observation, a distinct laminate structure with seven layers was quantitatively evaluated. A representative volume element (RVE) micromechanical computational method was developed and compared with the experimental results. Furthermore, homogenization method with the periodic boundary condition was implemented to evaluate the effective mechanical properties of the molded components. Finally, the phenomenological Johnson Cook (JC) model with fracture behavior was conducted to analyze the impact response of the injected components with different fiber orientation distributions. The new framework is demonstrated by acceptable energy absorption capability prediction of the SGFR PEEK composites.

Estimates of natural frequencies for nuclear vibration, and an assessment of the feasibility of selective ultrasound ablation of cancer cells

Selective ablation of cancer cells by ultrasound would be transformative for cancer therapy, but has not yet been possible. A key challenge is that cancerous and non-cancerous cells typically have similar acoustic impedance and are thus indistinguishable as materials in their responses to ultrasound. However, in certain cancers, cytoskeletal and nuclear lamin structures differ between healthy and malignant cells, opening the possibility of exploiting structural differences that manifest as different vibrational responses. To assess the possibility that the nuclei of certain cancerous cells might vibrate at different frequencies, we measured sizes and effective indentation moduli of a range of cancerous and non-cancerous cells from several cell lines and regions of the brain, and estimated the natural frequencies for nuclear vibration. Results suggest a potential difference in natural frequency for nuclear vibration between certain cancerous and non-cancerous cells, on the order of tens of kHz. This gap is potentially sufficient for selective ablation and motivates future experimentation on these specific cell types.

Analyses and control of interphase structures and adhesion properties of epoxy resin/epoxy resin for development of CFRP adhesion systems

In the adhesion of carbon fiber reinforced plastics (CFRP), the boundary regions were composed of only epoxy resins of CFRP matrix and adhesives, and their similar epoxy structures pose significant difficulty in studying the adhesion mechanism. Herein, we focused on structure and properties of laminates of epoxy resin substrates and adhesives with different curing conditions of substrates. We prepared laminates using deuterated epoxy adhesives or fluorinated epoxy adhesives, and their boundary regions were identified through confocal Raman scattering measurements. The regions were distributed into “penetration” and “interphase”. In particular, the penetration phase is a key of the adhesion properties. The penetration behaviors strongly depended on the crosslinking densities of the adherends, suggesting that the penetration regions would be directly impacted by the curing conditions of the substrates and molecular size of epoxy adhesive precursors. Our findings provide insights into novel designs of the reliable adhesion-based manufacturing systems of CFRP.

A bimodal and heterogeneous laminate structure with alternately distributed copper-base and nickel-base alloys via multi-material laser powder bed fusion (MM-LPBF) additive manufacturing

A micro-laminated bimodal heterostructure with alternately distributed copper-base and nickel-base alloys was additively manufactured via the multi-material laser powder bed fusion (MM-LPBF) technique. The high melting point elements such as nickel act as the heterogeneous nucleation sites for the copper melt, promoting the generation of ultrafine grains and forming a multi-layered structure with alternating coarse and fine grains. The differentiated grain size, shape and orientation in the bimodal heterostructure lead to the diversity of deformation mechanisms in different localized areas, which helps to achieve the internal stress gradient distribution and plastic deformation harmonization, thereby overcoming the strength-ductility trade-off for the overall structure. This work provides a novel fabrication path and experimental basis for understanding bimetallic laminated heterostructures.

Strength Lab AI: a mixture-of-experts deep learning approach for limit state analysis and design of monolithic and laminate structures made of glass

The demand for transparent building envelopes, particularly glass facades, is rising in modern architecture. These facades are expected to meet multiple objectives, including aesthetic appeal, durability, quick installation, transparency, and both economic and ecological efficiency. At the heart of facade design, particularly for structural glass elements, lies the assurance of structural integrity for ultimate and serviceability limit states with a requisite level of reliability. However, current structural engineering assessments for glass and glass laminate designs, especially in the geometrically non-linear setting, are time-consuming and require significant expertise. This study develops a customized Mixture-of-Experts (MoE) neural network architecture to overcome current limitations. It calibrates it on synthetically generated stress and deformation data obtained via parametrized Finite-Element-Analysis (FEA) of glass and glass laminate structures under both geometrically linear and nonlinear conditions for several joint support and loading conditions. Our findings reveal that the MoE model outperforms baseline models in predicting laminate deflections and stresses, offering a substantial increase in computational efficiency, compared to traditional linear and non-linear FEA, at high accuracy. The MoE is integrated within a novel web-based glass design and verification tool called Strength Lab AI and provided to the engineering public for future use. These results have profound implications for advancing engineering practice, offering a robust tool for the intricate structural design and analysis of glass and glass laminate structures.