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This study concerns the importance of curing kinetic models for the prediction accuracy of the thermal overshoot in the curing process of thick polymeric composite plates. An adaptive activation energy (AAE) method was proposed to determine an accurate curing kinetic model with adaptive activation energy (CK‐AAE). Then the temperature field model of the autoclave curing process was established based on the CK‐AAE equations for predicting the curing thermal overshoot of thick polymer‐matrix composite plates. The prediction accuracy of the curing degree using the CK‐AAE model was improved greatly compared with the common curing kinetic models. And the predicted curing thermal overshoot of thick polymeric composite plates yielded good agreement with the measured results from the autoclave curing experiments. Moreover, it was observed that the curing thermal overshoot was more susceptible to the laminate thickness and less affected by the stacking sequence. [ABSTRACT FROM AUTHOR]

• The influence of fiber cutting at the composite grid intersection on the compressive behavior of laminate is studied. • The varied compressive performance of laminate induced by different fiber cutting methods is considered. • The reduction in compressive strength and dominant failure modes are accurately predicted and revealed. For thick composite grid structure, automated fiber placement (AFP) must be adopted to alternating cut fiber at the composite grid intersection to avoid out-of-plane fiber bending. In the present work, an experimental and numerical study has been carried out to understand and predict the influence of different cutting methods at the composite grid intersection on the compressive failure performance of laminate. Five kinds of test specimens with different cutting ratios were firstly manufactured and tested. A maximum of 67% drop in the compressive strength was recorded for the most severe cutting ratio. A High-speed camera was used to clarify the compressive failure progress of cut specimens. The dominant failure mechanism was classified into fiber fracture failure and inter-ply delamination. Further, numerical simulations were carried out to inform the deformation and failure mechanism of cut specimens. The FEM results correlated well with experiments in terms of location of dominant failure mode and strength knockdown for five different cutting configurations. These findings offered certain practical reference for the design and manufacture of thick AFP composite grid structures. [ABSTRACT FROM AUTHOR]

• A layered pre-compaction scheme has been developed for curing ultra-thick composite laminates. • A novel uniaxial test method for ultra-thick composite laminates is proposed, and a heavy-duty compression test device is built. • High-modulus specimens have lower strength than low-modulus specimens due to premature delamination. • The test and simulation data of ultra-thick laminates are valuable reference for the design of ultra-thick structure. The damage mechanism of ultra-thick laminates widely used in aerospace and marine industries was obviously different from that of thin laminates. However, compression testing and simulation methods were generally limited to relatively thin laminates. To explore the compressive failure behavior of ultra-thick laminates, Firstly, a layered pre-compaction scheme was proposed to ensure the curing quality of ultra-thick laminates. A heavy-duty compression test equipment (accuracy reached 0.001 mm) was then developed, and a novel compression test method for ultra-thick composite laminates was proposed. The results showed that delamination played a key role in the failure behavior of ultra-thick laminates. The low interlaminar normal strength of ultra-thick laminates (55% of the 2 mm thin laminate) led to premature delamination, and wrinkle defects seriously reduced the compressive strength (11%). The compressive behavior for the matrix-dominant failure specimen predicted by the Puck criterion was the smallest (0.07%), while Tsai-Wu 3D predicted the smallest error (5.1%) for the delamination-dominant specimen. Finally, these findings are helpful for the design of ultra-thick composite structures. [Display omitted] [ABSTRACT FROM AUTHOR]

• A new method to improve the OHT strength of laminates by controlling different fine Z-pin arrangement angles was proposed. • The influence of Z-pins size parameters and the arrangement directions were investigated by experiments and simulations. • The tensile strength of fine Z-pin can reach 3500 Mpa without pore defects. • Fine Z-pins aligned 45°to the loading orientation improve open-hole tensile strength by up to 10%. The damage to structural performance caused by cut-out or holes is inevitable. In this paper, a new method to improve the tensile strength of open-hole laminates by using ultrasound-guided machine to control different fine Z-pin arrangement angles was proposed. The influence of systematically changing size parameters (0.11 mm, 0.28 mm and 0.5 mm diameters) and the direction of arrangement (unenhanced, parallel, vertical and 45° to the loading direction, respectively) were investigated by experiments and simulations. The production process of Ø 0.11 mm Z-pin with tensile strength up to 3500Mpa is firstly proposed. Z-pins with larger diameters have a certain inhibition effect on the depth of delamination damage, the connected resin-rich area seriously reduces the open-hole tensile strength when increasing the volume contents. In contrast, Ø 0.11 mm Z-pins can effectively reduce the strain level around the notch compared with the unpinned specimen. Ø 0.11 mm Z-pins aligned at 45° to the loading direction resulted in a 9% increase in open-hole tensile strength and a 54.1% reduction in delamination damage area. Finally, the simulation optimization is used to find that the 30° alignment has a better effect of suppressing delamination. [Display omitted] [ABSTRACT FROM AUTHOR]

• TE-GDQ method as the solver of highly coupled partial differential equations of motion. • FSDT theory to approximate the displacement field of composite conical shell. • Generalized Maxwell constitutive law for modeling the magnetorheological elastomer matrix. • Modified rule of mixture and Halpin–Tsai micromechanical rule to numerical homogenize the composite media. • Tunable dynamic and damping of structures by using the MRE materials in the composites. This study explores the dynamic behavior of axially loaded conical shells composed of magnetorheological elastomer composites (MRECs). The investigation focuses on analyzing the impact of compressive loads on the frequencies and loss factors of these composites. The MRECs consist of laminates reinforced with fibers, enabling tunable viscoelastic properties through the utilization of magnetic fields. The equivalent mechanical characteristics of the MREC are calculated using the modified Voigt and Halpin–Tsai micromechanical rules. By employing the first-order shear deformation theory and Sanders-based strains, the kinematics of the conical shell are accurately modeled. A semi-analytical analysis, combining trigonometric expansion and the generalized differential quadrature (GDQ) methods, is employed to solve the system's highly coupled partial differential equations. Two consecutive analyses are performed. Firstly, the critical buckling load of the MREC conical shell is obtained through a stability analysis. Subsequently, the frequencies and loss factors of the shell in the pre-buckling zone are computed. Parametric analyses are conducted to study the impact of key factors, including magnetic field strength, compressive load magnitude, composite properties, geometric parameters, and boundary conditions. The proposed methodology is rigorously validated through meticulous accuracy and convergence analysis. The outcomes provide valuable insights into the dynamic response of axially loaded magnetorheological elastomer composite conical shells, highlighting their potential in adjustable dynamic and damping systems. [ABSTRACT FROM AUTHOR]

[Display omitted] • A geometric reconstruction approach based on consolidation and sweeping formation is proposed to characterize gap geometry. • A mechanical model on effects of AFP gaps is developed to study delamination failure of curved laminates. • The effect of AFP gaps on the bending strength of curved laminates varies with gap orientations. • 45°oriented gaps in spatial distribution greatly reduce the bending resistance of laminated panels. Automated placement technology has been widely used due to its excellent processing adaptability for large composite components with complex geometric structures. Whereas, it still poses challenges to study the effect of manufactured gaps induced by automated placement on curved composite parts. This study proposes a new geometric reconstruction approach based on consolidation and sweeping formation to model manufactured gaps. Additionally, a mechanical model incorporating the reconstructed geometry and the cohesive layer method is established to predict the physical behaviors of curved laminates. The micrograph of automated placement-induced gaps with 90° orientation was used to verify the rationality of the geometric reconstruction approach of gaps forming in the preparation process of composite materials. According to predictions of the proposed mechanical model, the effect of − 45° oriented gap defects on curved laminates was validated via four-point bending tests that confirmed alignment between predictions and experimental results for peak load, crack propagation, and failure patterns. Experimental results show that due to the differences in spatial local geometric features, orientations of gap defects would reduce the bending strength to different degrees and significantly affect the failure pattern of curved laminates. Furthermore, curved laminates with wider gaps experience a more considerable reduction in load-bearing capacity. [ABSTRACT FROM AUTHOR]

Z-pinning is an effective method to improve the delamination resistance of composite laminates. The microstructure and manufacturing parameters have a great influence on the properties of z-pin composite laminates. In order to explore the influence of microscopic characteristic parameters on material properties and damage analysis, a parameterized RVE finite element model algorithm for automatic establishment of z-pin reinforced composites was proposed. The algorithm involves avoiding in-plane fibers to pin, generating fiber waviness, and assembling pin-fiber–matrix. Moreover, the statistical distribution of fiber misalignment angle can also be controlled. The developed program can generate RVE models with different parameters efficiently and quickly, such as fiber volume fraction, pin volume fraction, pin diameter, RVE size and fiber waviness. The statistical verification of the distribution of fiber misalignment angle can satisfy the probability distribution modeling of fiber angle. The generated model is divided into meshes, and finite element calculation can be realized. This work is of great significance to study the effects of microscopic characteristics on the properties and to optimize the design of z-pin reinforced composites. [ABSTRACT FROM AUTHOR]

The compressive strength drops sharply within 30 mm thick, but slowly when exceeding 30 mm thick. Delamination and fiber misalignment dominate the failure mechanism of ultra-thick laminate. Fiber waviness and voids contribute to the effect of thickness change on compressive strength. Higher interlaminar stresses S13 and S33 at the free edge induced premature delamination. As ultra-thick laminates are widely used in the field of aerospace and marine as the main load-bearing structure, extreme service conditions lead to increasing thickness of composite structures. However, the effect of the increase in thickness on the compressive properties of ultra-thick laminates is still unclear. Herein parameters including fiber volume fraction, fiber waviness, void content and free edge effect that affect the compressive strength with increasing thickness are studied. The results show that the fiber volume fraction of ultra-thick laminates does not change significantly with the increase of thickness due to the adoption of the zero-bleeding process, while the fiber waviness and void contribute to the thickness effect on compressive strength. On the other hand, the high interlaminar stress of the free edge contributes to the premature delamination of the specimen, which dominates the compressive strength of the ultra-thick laminate. Finally, compared with the thin laminate (2 mm), the compressive strength of ultra-thick laminate drops sharply (nearly 28%), but when the thickness increases from 30 to 70 mm, the drop of compressive strength is not obvious (only 10%). When the material and curing process are consistent, the weak interlaminar properties of ultra-thick laminates does not change significantly with the increase of thickness, which leads to the insignificant decrease in compression strength of ultra-thick laminates with the increase of thickness. The proposed empirical relationship between the compressive strength and thickness of quasi-isotropic laminates can provide important theoretical basis and experimental reference for the design of ultra-thick composite structures. [Display omitted] [ABSTRACT FROM AUTHOR]