The fracture processes of the constant/variable stiffness composite laminate (CSCL/VSCL) subjected to uni-axial tension is investigated using the phase-field method. The main objectives of this work ...are: (a) to study the crack propagation path and (b) to investigate the influence of the fiber-matrix interface on the crack path. In particular, the emphasis is to explore the role played by the orientation of the fiber and the inter-fiber spacing on the fracture pattern in the composite. From the numerical study, it is inferred that: (a) the cracking pattern of the composite is significantly influenced by the orientation of the fiber and (b) the load carrying capacity of the composite enhances with the increase in the orientation of the fiber. For a larger inter-fiber spacing, the load-displacement curve does not alter significantly for different orientations of the fiber. Furthermore, a novel approach to predict the load-displacement curve of the composite using an equivalent homogenized orthotropic material is presented, showing a very good agreement between them. It is seen that the location of the crack in the VSCL influences the failure load.
In the present article, Reddy shear deformation plate theory is employed to investigate the free vibration of vertical laminated composite plates coupled to sloshing liquid. Two different types of ...composite plate are considered; hybrid composite laminate (HCL) plate, which consists of two types of fiber, and variable stiffness composite laminate (VSCL) plate, which is made of curvilinear fibers. The applied Reddy shear deformation theory introduces a nonlinear through-thickness distribution for the transverse shear stress, and it satisfies the zero stress conditions at the bottom and top surfaces of the plate. The sloshing fluid, which is partly in contact with the plate, is modeled as ideal, and the bulging and sloshing modes related to that are calculated using the fluid velocity potential. The interaction between fluid and solid is modeled through the continuity equation and boundary conditions at the fluid–solid interface. To extract the vibrational characteristics of the structure coupled to fluid, a polynomial approximation based on the Rayleigh-Ritz method is employed. After validating the proposed methodology, a parametric study is conducted to show the effects of various parameters associated with the fluid and structure on the natural frequencies of the system.
In many structural applications, such as marine, aircraft and so on, structures are designed to withstand high impact loading, because they may be subjected to impact of the projectiles with high ...velocity 1,2 . Fabrics become good choice to resist impact of ballistic 3 because of light weight and high specific strength .
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•Impact behavior of bio-inspired helicoidal laminates with non-linear rotation angle.•Proposing three types of non-linear helicoidal configurations.•An effective model to predict ...damage development of fiber, matrix and delamination.•Revealing damage of helical fiber, matrix cracking path and enhancing mechanism.
Through evolutionary process, special biological structures (e.g. micro- or macro-scale helicoidal laminated structures) are formed naturally to resist natural enemies. With some bionic inspirations, anti-impact design of composite laminates applied for aerospace, vehicle, etc. can be stimulated by helicoidal biological structures. In the work, the Non-Linear Rotation Angle (NLRA) based bio-inspired helicoidal layups are designed to enhance the impact resistance capacity of composite laminate. Four types of helicoidal configurations are proposed including Quasi-isotropic (QI), Helicoidal-Recursive (HR), Helicoidal-Exponential (HE) and Helicoidal-Semicircular (HS). The failure behaviors of material are investigated with the progressive damage model. Damage development of fiber, matrix and delamination interface is conducted with stress-based failure criteria, fracture energy criteria and stiffness degradation method. The impact damage behaviors of carbon/epoxy composite laminates with QI and NLRA helicoidal layups are studied and compared. Further, effects of coefficients in each layup formula are discussed. Numerical results show that predicted load-time curve and damage modes for QI correlate well with experimental results. It is revealed that both the maximum resistance load and threshold load for the initial matrix damage and delamination increase with the increase of each coefficient. As compared with QI layup, HR and HE layups with large rotation angles can improve the capacity of impact resistance.
Impact resistance and damage tolerance are of great significance in the design of composite structures. This study investigated the damage and failure mechanism of thin composite laminates under ...low-velocity impact and compression-after-impact (CAI) loading conditions. Four levels of impact energy were included in the test matrix. Delamination induced by low-velocity impact was captured using ultrasonic C-scan, and a three-dimensional (3D) digital image correlation (DIC) system was employed to measure full-field displacement during the CAI tests. Infrared thermography was also used to online monitor the thermal field variation of the test specimen during the impact and CAI process. The cross sections of typical tested specimens were inspected using an optical microscope and a scanning electron microscope (SEM). A 3D damage model that considers both interlaminar and intralaminar damage was proposed to study the complex damage and failure mechanism. Excellent correlation was obtained between the experimental results and the numerical results. The experimental results obtained from various tests and the results from the numerical simulation were combined to provide a new and deep insight of damage evolution and failure mechanisms under low-velocity impact and CAI loading conditions.
Composite laminates (CFRP, GFRP, and fiber metal composite laminates) are attractive for many applications (such as aerospace and aircraft structural components) due to their superior properties. ...Usually, mechanical drilling operation is an important final machining process for components made of composite laminates. However, composite laminates are regarded as hard-to-machine materials, which results in low drilling efficiency and undesirable drilling-induced delamination. Therefore, it is desirable to improve the cost-effectiveness of currently-available drilling processes and to develop more advanced drilling processes for composite laminates. Such improvement and development will benefit from a comprehensive literature review on drilling of composite laminates. This review paper summarizes an up-to-date progress in mechanical drilling of composite laminates reported in the literature. It covers drilling operations (including conventional drilling, grinding drilling, vibration-assisted twist drilling, and high speed drilling), drill bit geometry and materials, drilling-induced delamination and its suppressing approaches, thrust force, and tool wear. It is intended to help readers to obtain a comprehensive view on mechanical drilling of composite laminates.
•Guided ultrasonic wavefield measurements performed on quasi-isotropic CFRP laminate.•Scattering at artificial, ellipse delamination, located at an asymmetric depth.•Wave trapping on top of ...delamination and forward scattered wave verified.•Numerical, Finite Element simulations validated from experiments.•Parameter study of guided wave scattering at different delamination shape and depth.
Carbon fibre composite laminates are increasingly being used for aerospace structures due to their low weight and improved mechanical performance. Impact damage can cause delaminations below the visible surface of the structure due to limited interlaminar strength. Guided ultrasonic waves can detect and characterize delaminations in composite laminates. The scattering of the A0 Lamb wave mode at an artificial delamination, located at an asymmetric depth in a quasi-isotropic laminate, was investigated. Full field non-contact laser measurements were used to visualise wave trapping and scattered waves. A three-dimensional finite element model was developed and validated against the experiments. The influence of delamination shape and depth on guided wave scattering were studied. Small variations in delamination shape significantly affected the interference pattern on top of the delamination, but had limited effect on the scattered wave outside the delamination. Delamination depth was found to strongly influence the angular direction and amplitude of scattered waves. Implications for structural health monitoring were discussed.
Reversible deformable structures manufactured by four-dimensional (4D) printing have potential applications in numerous fields, such as actuators, intelligent mechanisms, and soft robots. In this ...study, a novel low-cost approach for realizing reversible structural deformation by fused deposition modeling (FDM) 4D printing is proposed, which combines the thermodynamic properties of an elastomer material (thermoplastic polyurethane, TPU) and a shape-memory material (polylactic acid, PLA). PLA with stored pre-strain (which has a storage modulus that changes greatly with temperature) was used as the active layer, while TPU (which has a stable storage modulus) was used as the passive layer. A mathematical model was established to analyze the versatility of this combination of materials and clarify the requirements of the related materials. The experimental deformation results of the composite laminate structures (whose properties were controlled by the printing parameters and structural parameters) were consistent with the simulation results, and the deformation trends were consistent with the trends obtained by the mathematical model. A variety of models were manufactured using the composite laminate, which can realize reversible complex deformation with simulation pre-programming. This strategy is scalable, and the basic design principles have broad application prospects in reversible 4D printing.
