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• A series of new irregular architected materials is generated from diverse stretch- and bending-dominated building blocks. • An end-to-end deep learning strategy is innovatively developed to achieve stiffness prediction and inverse design of irregular architected materials. • We provide mechanical interpretations for irregular architected materials with programmable anisotropic stiffness. • The deep learning strategy can accurately and efficiently hit the targeted stiffness beyond the dataset. Incorporating biological materials-inspired irregularity into architected materials is potential to unfold a wider property or new function space, while the inverse design of irregular architected materials (IAMs) for targeted properties is still challenging, owing to the intricate structure–property bidirectional relationships. Accordingly, here, a data-driven framework is originally developed to design new irregular architected materials with programmable stiffness. In detail, a robust dataset of IAMs, which are constructed from diverse stretch- and bending-dominated building blocks, is created by a randomized strategy, and an end-to-end deep learning model is established, including a forward and an inverse network. The forward predictions reveal that IAMs exactly achieve a wide space of programmable stiffness, especially, including extremely high or low dominant elastic stiffness C 11 , C 22 and C 66. More importantly, the deep learning-driven inverse design flexibly and precisely realizes the generation of IAMs, fulfilling the customized stiffness targets. Especially, various stiffness tensors, including isotropic, orthotropic, and anisotropic types, are successfully achieved. The remarkable advantage of the inverse design is that solely through adjusting the frequency hints of building blocks, without mandatory geometrical symmetry, IAMs present the exclusive ability to hit the targeted stiffness. Overall, this work fills the gap in the inverse design of irregular architected materials with programmable stiffness and paves the way for material design via deep learning. [ABSTRACT FROM AUTHOR]

This study introduces an ultrasonic vibration assisted resin transfer molding (RTM) technique as an innovative approach to address the inherent challenges associated with traditional methods for producing CFRP laminates. It investigates the mechanism of void formation in CFRP composites under ultrasonic vibration using 3D X-ray microscopy. Numerical calculations and simulation analyses are also employed to validate the impact of ultrasonic vibration on mechanical properties of CFRP. The findings indicate that ultrasonic vibration results in CFRP laminates with more uniform thickness, leading to a substantial increase in fiber volume fraction up to ∼16 %. Concurrently, there are significant improvements in flexural strength (∼20 %) and fracture energy (∼90 %). Ultrasonic vibration also effectively reduces CFRP porosity by at least 25 %, resulting in a more consistent distribution of voids, primarily consisting of small circular voids. This porosity reduction is attributed to the cavitation effect and enhancing wettability, consequently improving the mechanical properties of CFRP. Moreover, simulations and numerical calculations demonstrate the significant occurrence of cavitation effect within the resin under specific process conditions. The intensity of cavitation is influenced by factors such as the initial bubble radius, acoustic pressure amplitude, and static pressure of the resin. The ultrasonic-assisted RTM process is proved as a promising method for producing CFRP laminates with superior properties. [ABSTRACT FROM AUTHOR]

Additive manufacturing technology has been increasingly applied to fabricate continuous fiber reinforced thermoplastic composites for its potential in fabricating complex structures. Owing to the limited thermal and mechanical properties of the matrix, it is a critical trend to develop high-performance thermoplastics to widen engineering applications. This study aims to comprehensively investigate the properties of the prepared CCF/PEEK filaments together with their printed composites. The filaments were fabricated via a thermo-mechanical coupling process and were characterized by micromorphology observation, thermal and mechanical test. It was found that the impregnation behavior, thermal stability and mechanical performance of the filaments were improved with the increase of mold temperature and decrease of traction speed. The performance of printed specimens was evaluated by mechanical test and fracture analysis. It was concluded that the additive manufacturing process promoted the secondary impregnation behavior of the filaments. Higher nozzle temperature and bed temperature together with lower layer thickness and printing speed enhanced the tensile strength of printed specimens with maximum value reached 509.56 MPa. Besides, the analysis of failure mechanism indicated that filament fracture, horizontal cracks and filament pullout together with fiber breakage, fiber pullout, unimpregnated fibers and pores were the dominant failure modes for all printed specimens. [ABSTRACT FROM AUTHOR]

Machining strategy can significantly influence surface integrity when producing holes in CFRP laminate, which has drastic impact on mechanical behavior and service life of related structures. Therefore, it is vital to understand the effect of defects caused by machining on cracking/splitting initiation, propagation and final failure modes. In this paper, the influence of four different machining processes used to produce 6.0 mm diameter holes in CFRP was investigated in relation to mechanical behaviour under tensile loading. The processes involved were high power fiber laser cutting, abrasive waterjet machining, conventional drilling and ultraviolet laser multiple-pass machining. The complex strain distributions around the holes were analyzed using digital image correlation (DIC) method, while crack propagation was studied using high speed imaging technique. The correlation between initial surface integrity and mechanical behavior was developed. Stress concentrations and machining defects around holes accelerated damage accumulation with final failure modes highly related to fiber orientations rather than initial surface damage. [ABSTRACT FROM AUTHOR]

Pre-tension is well known as an effective approach to suppress forming defects caused by excessive shearing in manufacture process of the fabric reinforced composites. While, the coupling between shear and pre-tension of the fabrics is not thoroughly understood. Here, this work aims to explore and understand the meso/macro scale response of the comingled glass-polypropylene 2-2 twill woven fabric under shear pre-tension coupling. A self-developed picture frame fixture including a concise approach to apply pre-tension in shear experiments of the fabric was originally developed. Then, systematical shear experiments confirm that the critical shear angle of the fabric is 40°, as the fabric suffers in-plane complex deformations when the shear angle is above 40°. Additionally, the pre-tension significantly enlarges the shear force when the shear angle is lower than critical value of 40°. In view of mesoscopic scale, the pre-tension suppresses the undulation of the un-sheared fabric surface, revealing an enhancement of the coupling effect at the initiation of the shear deformation. Besides, the pre-tension also reduces the variation of yarn width. While, these mesoscopic effects caused by pre-tension are not pronounced when it is higher than 1.2 N/mm. The devised picture frame fixture and the exploration of the shear pre-tension coupling behavior provide an important experimental basis to the purpose of suppressing forming defect and to raise the manufacture efficiency of the fabric reinforced composites. [ABSTRACT FROM AUTHOR]

Due to suffering the thermal and mechanical loadings simultaneously, metamaterials integrating with the customizable coefficient of thermal expansion (CTE) and high mechanical performances are desirable to ensure the thermal and structural stabilities in engineering devices. Hence, various multi-phase metamaterials with programmable CTEs and mechanical performances were developed. Specifically, inspired by the mixture of multiple phases in composites and the rigid rotations of framework structures in materials with negative CTE, a typical pyramid unit was introduced. Additionally, two series of metamaterials were systematically designed, which were constructed in batches from different units through the matrix transformation method. The CTEs of the metamaterials were theoretically established and analyzed. Besides, mechanical performances, including relative density, stiffness and strength were also calculated and discussed. The results suggest that the directionality and magnitude of CTEs are determined by the constructing principle of multi-fold rotations. In addition, the large ranges of programmable CTEs and high load-bearing capacity are available in the devised metamaterials by reasonably modulating the geometrical parameters. The thermal expansion and mechanical performances of the metamaterials could be synchronously programmed. The diversity of the phase configurations and geometrical architectures in the metamaterials offers the opportunity to satisfy manifold requirements in different applications. [ABSTRACT FROM AUTHOR]

Abstract Current integrated thermal protection systems (ITPS) are generally devised with single layer metal sandwich panel and uniform insulation material, inevitably leading to limited thermal insulation effect and high risk of buckling failure. By contrast, here, ITPS, which incorporates graded insulation materials and multilayer ceramic matrix composite cellular sandwich panels, is devised to raise both thermal insulation effect and buckling strength. The effective thermal and mechanical properties are theoretically established. Transient heat transfer characteristics are numerically calculated. The results reveal that ITPS with specific graded insulation materials can present lower temperature and better temperature distribution uniformity than those of ITPS filled with uniform insulation material, demonstrating that graded insulation layers can firmly enhance the insulation effect. Besides, the insulation effect of ITPS, in which the densities and thermal conductivities of graded layers are taken arranged from low to high, is much better than those of ITPS which have opposite sequence. Moreover, the buckling strength is demonstrated to be significantly improved through the approach of integrating multilayer sandwich panels. The thermal short effect can be also suppressed, since it is demonstrated that the multilayer sandwich panels in the ITPS can reduce the temperature on bottom facesheet and raise the temperature distribution uniformity. [ABSTRACT FROM AUTHOR]

Tailoring thermal expansion of structures is in urgent need in engineering applications where the structures are susceptible to suffer large temperature fluctuation. Here, a method to reconstruct 3D truss structures is developed to obtain large positive, zero and even negative coefficient of thermal expansion (CTE). As the basis, theoretical analysis and numerical verification of the bi-material pyramid and tetrahedron lattice cells explicitly reveal that with thick members, the influence of the cross section on the CTEs should be well considered, and the CTEs should be accurately calculated by the solid model. Furthermore, two kinds of 3D lattice structures with isotropic tailorable CTEs are originally devised. Moreover, bi-pyramid and bi-tetrahedron units are devised, and a reconstruction method, which can reconstruct an arbitrary 3D truss structures to obtain specific target CTE, is originally developed. Typical supporting structure and platform used in satellites are reconstructed by the proposed method, and near zero thermal expansion, which is urgent needed in satellite, can be flexibly obtained. The analysis and proposal of three dimensional lattice structures and reconstruction method provide a new approach to develop structures with light weight and tailorable CTEs. [ABSTRACT FROM AUTHOR]

The engineering materials and structures, which usually suffer both temperature variation and mechanical loading, motivate the urgent need of the multifunctional metamaterials with simultaneously programmable coefficient of thermal expansion (CTE) and Poisson's ratio (PR). Whereas, the current 3D metamaterials can not continuously program the CTE and PR. Herein, a class of 3D metamaterial is originally devised by an exclusive geometrical methodology. The explicit expressions of the CTE and PR are theoretically established and are also verified by the numerical modeling. The analysis confirms that the CTE can be widely tailored by varying the geometrical parameters and selection of the constituents. Besides, the controllable PR can be also easily obtained by adjusting the geometrical parameters. Moreover, the devised 3D metamaterial gives paired tailorable CTE and controllable PR, including especially negative CTE + negative PR. An arrangement rule is developed to construct a series of hierarchical cells which can program CTE and PR in multi principle axes and can be periodically arrayed for obtaining the 3D cellular metamaterials. The devised 3D metamaterials are capable of realizing the widely coupled programmability of both CTE and PR and provide a strategy of shape morphing stimulated both by temperature variation and mechanical loading. [ABSTRACT FROM AUTHOR]