Fiber Reinforced Polymer Composite Laminates Research Articles

Mechanical Characterization of Hybrid Steel Wire Mesh/Basalt/Epoxy Fiber-Reinforced Polymer Composite Laminates

Hybrid composite materials have been widely used to advance the mechanical responses of fiber-reinforced composites by utilizing different types of fibers and fillers in a single polymeric matrix. This study incorporated three types of fibers: basalt woven fiber and steel (AISI304) wire meshes with densities of 100 and 200. These fibers were mixed with epoxy resin to generate plain composite laminates. Three fundamental mechanical tests (tensile, compression, and shear) were conducted according to the corresponding ASTM standards to characterize the steel wire mesh/basalt/epoxy FRP composites used as plain composite laminates. To investigate the flexural behavior of the hybrid laminates, various layer configurations and thickness ratios were examined using a design of experiments (DoE) matrix. Hybrid samples were chosen for flexural testing, and the same procedure was employed to develop a finite element (FE) model. Material properties from the initial mechanical testing procedure were integrated into plain and hybrid composite laminate simulations. The second FE model simulated the behavior of hybrid laminates under flexural loading; this was validated through experimental data. The results underwent statistical analysis, highlighting the optimal configuration of hybrid composite laminates in terms of flexural strength and modulus; we found an increase of up to 25% in comparison with the plain composites. This research provides insights into the potential improvements offered by hybrid composite laminates, generating numerical models for predicting various laminate configurations produced using hybrid steel wire mesh/basalt/epoxy FRP composites.

Enhancing Flexural Strength of RC Beams with Different Steel–Glass Fiber-Reinforced Polymer Composite Laminate Configurations: Experimental and Analytical Approach

This study intended to measure the efficiency of different strengthening techniques to advance the flexural characteristics of reinforced concrete (RC) beams using glass fiber-reinforced polymer (GFRP) laminates, including externally bonded reinforcement (EBR), externally bonded reinforcement on grooves (EBROG), externally bonded reinforcement in grooves (EBRIG), and the near-surface mounted (NSM) system. A new NSM technique was also established using an anchorage rebar. Then, the effect of the NSM method with and without externally strengthening GFRP laminates was studied. Twelve RC beams (150 × 200 × 1500 mm) were manufactured and examined under a bending system. One specimen was designated as the control with no GFRP laminate. To perform the NSM method, both steel and GFRP rebars were used. In the experiments, capability, as well as the deformation and ductileness of specimens, were evaluated, and a comparison was made between the experimental consequences and existing standards. Finally, a new regression was generated to predict the final resistance of RC beams bound with various retrofitting techniques. The findings exhibited that the NSM technique, besides preserving the strengthening materials, could enhance the load-bearing capacity and ductileness of RC beams up to 42.3% more than the EBR, EBROG, and EBRIG performances.

Enhancing the Longitudinal Compressive Strength of Freeform 3D-Printed Continuous Carbon Fiber-Reinforced Polymer Composite Laminate Using Magnetic Compaction Force and Nanofiber Z-Threads.

Low fiber-direction compressive strength is a well-recognized weakness of carbon fiber-reinforced polymer (CFRP) composites. When a CFRP is produced using 3D printing, the compressive strength is further degraded. To solve this issue, in this paper, a novel magnetic compaction force-assisted additive manufacturing (MCFA-AM) method is used to print CFRP laminates reinforced with carbon nanofiber (CNF) z-threads (i.e., ZT-CFRP). MCFA-AM utilizes a magnetic force to simultaneously levitate, deposit, and compact fast-curing CFRP prepregs in free space and quickly solidifies the CFRP laminate part without any mold nor supporting substrate plate; it effectively reduces the voids. The longitudinal compressive test was performed on five different sample types. ZT-CFRP/MCFA-AM samples were printed under two different magnetic compaction rolling pressures, i.e., 0.5 bar and 0.78 bar. Compared with the longitudinal compressive strength of a typical CFRP manufactured by the traditional out-of-autoclave-vacuum-bag-only (OOA-VBO) molding process at the steady-state pressure of 0.82 bar, the ZT-CFRP/MCFA-AM samples showed either comparable results (by -1.00% difference) or enhanced results (+7.42% improvement) by using 0.5 bar or 0.78 bar magnetic rolling pressures, respectively.

Improving resistance to embedded delaminations by adding CNTs to epoxy in carbon/(epoxy + CNT) composites

Low-velocity impact on fiber-reinforced polymer (FRP) composites may cause subsurface interface delaminations. In the case of such multiple delaminations, neighboring delaminations may grow and coalesce into larger delamination under post-impact loading. The resistance to such growth is substantially influenced by the strength and stiffness of epoxy resins used in FRP composite laminates. Therefore, the current study attempts to determine how adding carbon nanotubes (CNTs) to epoxy might potentially enhance the resistance to such delaminations. A three-dimensional (3D) finite element analysis has been carried out for laminates having single embedded delamination as well as two neighboring embedded delaminations to determine the interlaminar stresses and strain energy release rate using virtual crack closure integral. Results from the current analysis show that while parameters like shape, size, and relative spacing of delamination influence the growth, however in all the cases, adding CNTs to epoxy significantly improves the resistance to the growth of both single and interacting delaminations. The effect is observed to be more pronounced when the delaminations are closely spaced and tend to coalesce into a large delamination.

A comparative study on the low velocity impact behavior of UD, woven, and hybrid UD/woven FRP composite laminates

This study is aimed at comparing the response and damage of unidirectional (UD), woven fabric (WF) and hybrid UD/WF fiber reinforced polymer (FRP) laminates subjected to low velocity impact. The unidirectional tape and/or woven fabric (plain weave) carbon/epoxy prepregs are laminated and hot-pressed to produce UD, WF and sandwich-like hybrid UD/WF specimens. Impact responses of specimens are determined through low velocity impact (LVI) tests with impact energies of 10 J, 17 J and 25 J. After the LVI tests, the damage of specimens is characterized and analyzed using a combination of visual inspection, ultrasonic phased-array inspection, micro-computed tomography (CT) inspection, cross-sectional microscopic observation, and thermal de-ply test. Also, the LVI damage mechanisms of the three types of specimens are quantitatively compared by using the inter fiber crack volume ratio, total delamination area and fiber fracture length. It is concluded that the fiber architecture plays an important role in determining low velocity impact behavior of composite laminates. Especially, for the sandwich-like hybrid UD/WF laminates whose surface is a WF layer and the core is a UD layer, the WF layer on the surface plays an important role in reducing matrix cracking, delamination and fiber fracture, thus improving its LVI resistance.

Fatigue damage mechanisms and evolution of residual tensile strength in CFRP Composites: Stacking sequence effect

This study explores the effect of fiber orientation on the fatigue resistance of carbon fiber reinforced polymer composite laminates. First, fatigue damage mechanisms of composite laminates with different stacking sequences at various stress levels are analyzed by utilizing digital image correlation (DIC) and scanning electron microscope (SEM) techniques. The findings highlight that the fiber orientation of the laminate has a significant effect on the fatigue life of the specimens. Prior to final fatigue failure, laminates with 0° fiber orientation experience only a 30 % reduction, while laminates with ± 45° fiber orientation show up to 93 % stiffness reduction. The fracture modes of laminates with a 0° fiber orientation vary depending on stress levels. Microscopic observations confirm that in the case of laminates with ± 45° fiber orientations under compressive loading, fiber flexion, and delamination are the predominant failure mechanisms. Further, the post-fatigue tensile tests reveal that the residual tensile strength of the laminates with ± 45° fiber orientations increases by 6.3 % after 15 % of the total cycles (7.2 × 104) at a 30 % stress level. The contribution of this study provides vital insights into the structural design of laminates and offers a pathway for improving their fatigue performance.

Study of the dynamic response and damage evolution of carbon fiber/ultra-thin stainless-steel strip fiber metal laminates under low-velocity impact

Two configurations of carbon fiber/ultra-thin stainless-steel strip fiber metal laminates (CUSFML) with differing metal volume contents (35.3% and 18.2%) and carbon fiber-reinforced polymer (CFRP) composite laminates were selected for tests. The impact response and the effect of metal volume content on the impact resistance of CUSFML were assessed via experiment and FEM. Inducing damage by drop-weight test within the impact energy range of 18.60–46.23 J, two types of CUSFML and CFRP composite laminates were compared. In particular, the bearing capacity, impact deflection, failure modes, and energy dissipation were considered. The impact modeling using the VUMAT subroutine refines the relationship between energy-dissipating mechanism and damage evolution. The results indicate that CUSFML are characterized by higher impact resistance than CFRP composite laminates under low-velocity impact. The effect of metal volume content on the impact resistance increases gradually with impact energy increasing. Under 46.23 J impact, the CUSFML with higher metal volume content exhibits more concentrated damaged area with severe penetration failure, which is more dominated by metal failure features with a higher proportion of plastic energy dissipation. For CUSFML with lower metal volume content, extensive delamination and damage expansion occurs under the dominance of fiber damage behaviors.

Hybrid effects and failure mechanisms of carbon/Kevlar fiber composite laminates under the bending-after-impact loading

The hybrid fiber design concept is widely used in the aerospace industry to improve the mechanical properties (stiffness, strength, elongation, energy absorption ability) of composite laminates. In the present work, an experimental method was employed to investigate the hybrid effects on the failure mechanism of carbon-Kevlar hybrid fiber-reinforced polymer (HFRP) composite laminates under bending-after-impact (BAI) loading conditions. Carbon/Kevlar FRP specimens with five different hybrid ratios and three different stacking sequences were designed and fabricated by the compression molding method. A series of three-point bending (3 PB) tests and BAI tests were conducted to characterize the degradation of the residual flexural properties of the laminates under low-energy impacts. Among the laminates designed with different hybrid ratios, the [K3C3] structure combined the advantages of the high strength of carbon fibers and the high toughness of Kevlar fibers; thus, it exhibited excellent residual bending properties. Among the laminates designed with different stacking sequences, the outermost Kevlar fiber layer in the [KCC]S structure effectively protected the inner carbon fiber layers on the compressed and stretched sides; thus, it yielded excellent residual flexural properties.

Integrated composite electrothermal de-icing system based on ultra-thin flexible heating film

Icing is a serious threat to the flight safety of aircraft. Lightweight and efficient electrothermal de-icing systems for carbon fiber reinforced polymer components are expected to contribute to the lightweighting and electrification of aircraft. This study presents the development and test of a novel, integrated, multifunctional composite electrothermal ice protection system. The system achieves this by incorporating a carbon-based ultra-thin flexible heating film into a carbon fiber-reinforced polymer composite laminate. T700 and M40 carbon fiber prepregs were used. The system composition and configuration were designed based on the anisotropic mechanical and thermal properties of the carbon fiber-reinforced polymer composite. The effects of ply stacking sequence, presence of insulation layer, ply angle, heating area, and prepreg type on thermal response and de-icing performance were investigated. Thermal response experiments were carried out in both room temperature and low temperature environments. A one-dimensional thermal response analysis model was developed for a representative heating structure. Comparative de-icing experiments were conducted on different samples in a low-temperature test chamber. A numerical model, based on the modified enthalpy-porosity method, was developed to simulate the de-icing process, and showed good agreement with the experimental results. Experiments and numerical calculations show that the arrangement of the heater close to the deicing surface improves the performance of the electrothermal deicing system while maintaining the overall mechanical properties of the multi-layer structure. While the insulation layer helps marginally with heat loss during de-icing, it significantly increases the system’s thermal inertia, which delays the de-icing’s start. It is recommended to minimize or eliminate insulation layer thickness. Rapid de-icing effects, combined with energy conservation, can be achieved through a short-term, high-power heating strategy.

Analysis of unidirectional polyethylene-glass fiber-reinforced phenolic polymer composite laminate

Analysis of unidirectional polyethylene-glass fiber-reinforced phenolic polymer composite laminate

Polysulfone nanofiber-modified composite laminates: Investigation of mode-I fatigue behavior and damage mechanisms

In this study, the fatigue properties of carbon fiber-reinforced polymer (CFRP) composite laminates were investigated, specifically focusing on the incorporation of 100-µm polysulfone (PSU) nanofibers as an interleaving material. The PSU nanofibers were produced using the electrospinning technique. Both quasi-static and fatigue tests were conducted on both the reference specimens and the modified specimens to evaluate their mode-I performance. The results revealed an 85% increase in fracture toughness (GIC) under quasi-static testing. The fatigue plots revealed a noteworthy reduction in the fatigue crack growth rate (da/dN) for the modified specimens due to new toughening mechanisms. Scanning electron microscopy (SEM) demonstrated that, the PSU nanofiber became melted and distributed in the interface, leading to phase separation and a sea-island structure. The presence of PSU microspheres caused crack deflection during delamination, which resulted in increased fracture and fatigue resistance.

Experimental study of the interfacial micromechanics of multifunctional unidirectional carbon fiber reinforced polymer composite laminates with copper mesh

The mechanical properties of a unidirectional carbon-fiber reinforced polymer (CFRP) laminate with Cu mesh layers were investigated for use in aerospace applications as a multifunctional structural and electromagnetic interference shielding component. Nanoindentation was used to study the fiber/PEEK and Cu/PEEK interfaces. A data analysis methodology is presented to assess the interfacial strength from plots of hardness and modulus versus distance from fiber/Cu edge. The results indicated that annealing resulted in enhanced adhesion at the fiber/PEEK interface. Additionally, indents near the Cu/PEEK interface indicated poor interfacial adhesion. Bulk mechanical testing was performed to determine the effect of adding Cu mesh layers on the mechanical properties of the laminate. Additional Cu mesh layers decreased the tension, shear, and bending strength/modulus, while the open hole compression strength increased. This indicates that the Cu/PEEK interfaces weaken the laminate and lower the tension, shear, and bending strength by delamination.

Deep reinforcement learning for stacking sequence optimization of composite laminates

Fiber reinforced polymer (FRP) composite laminates are increasingly used in a wide range of safety–critical products due to their excellent material properties. The stacking sequence of FRP composite laminates plays a critical role in the resulting part’s mechanical properties. Despite this, composite engineers still commonly fabricate parts with “classic” ply layups (e.g. four ply laminate with fiber orientation angles: [-45/0/45/90°]), which may have sub-optimal mechanical performance in the expected loading/use cases. Finding the composite stacking sequence that achieves the best material and mechanical properties possible is a challenging optimization problem characterized by the large domain space involved in solving an inverse design problem. This paper introduces a novel approach to optimizing stacking sequence for composite plate stiffness by applying off-policy deep reinforcement learning (DRL). We formulate the problem as a sequential decision making process. The state of the system is based on the stiffness of the composite for the currently selected stacking sequence and the action is to select a new stacking sequence using our reward function, formulated as the offset, normalized stiffness modulus. We compare our DRL model to two classical stacking sequences, a randomized baseline model, and a competitive genetic algorithm (NSGA-II). For maximizing longitudinal composite plate stiffness, the DRL model finds the optimum solution for all ply thicknesses and the genetic algorithm comes within 0.5% of the optimum. The DRL model determines the optimum stacking sequence significantly faster and is less sensitive to parameter tuning. The DRL model and the genetic algorithm both outperform the random baseline algorithm by over 5.7 standard deviations in the most conservative case. This research demonstrates the ability of DRL to effectively and efficiently optimize composite laminate stacking sequence.

An Overview of Angle Deviations of Fiber-Reinforced Polymer Composite Angular Laminates.

After manufacturing, fiber-reinforced polymer composite laminates may have residual stresses, resulting in warpage in flat structures and angle changes in angular sections. These shape distortions may cause fitting mismatch problems under high-level assembly, and extra efforts to fix these problems may be needed. The present paper only makes an overview of the angle deviation of angular composite laminates made of either thermoset matrix with autoclave curing or thermoplastic matrix with thermoforming. Depending on the positive or negative angle deviation, spring-back or spring-in behavior is observed. There are many parameters, including intrinsic and extrinsic parameters, that could affect the angle deviation. In the first part of this review paper, experimental results concerning the effects of the part angle, part thickness, lay-up sequence, corner angle, flange size, tool material, tool surface, and cure cycle are summarized. Spring-in angles are generally obtained in this part. In the second part, several prediction methods, such as simple equations and finite element methods, are compared to indicate the considered parameters. Some have good agreement and some have larger errors. The crucial differences may be dependent on the micromechanical theories and the input properties of the composite and the constituents.

Fabrication of Glass Fiber-Reinforced Polymer (GFRP) Composite Laminates by Wet Hand Lay-Up/Vacuum Bag (WLVB) Method

Fabrication of Glass Fiber-Reinforced Polymer (GFRP) Composite Laminates by Wet Hand Lay-Up/Vacuum Bag (WLVB) Method

Impact Property Characterization of Glass Fiber-Reinforced Polymer (GFRP) Composite Laminates

Impact Property Characterization of Glass Fiber-Reinforced Polymer (GFRP) Composite Laminates

Optimization Design and Nonlinear Bending of Bio-Inspired Helicoidal Composite Laminated Plates

Inspired by the bionic Bouligand structure, helicoidal carbon fiber-reinforced polymer composite (CFRPC) laminates have been proven to own outstanding out-of-plane mechanical properties. This work aims to further explore the excellent bending characteristics of helicoidal CFRPC laminated plates and find out the optimal helicoidal layup patterns. The optimization design of laminated plates stacked with single-form and combination-form helicoidal layup sequences are carried out by using the finite element method (FEM) and adaptive simulated annealing (ASA) optimization algorithm on the Isight platform. Then, the nonlinear bending responses of optimal helicoidal CFRPC laminated plates are investigated via the FEM for the first time. The helicoidal CFRPC laminated plates under three different types of boundary conditions subjected to transverse uniformly distributed load are considered. The numerical results reveal that the combination-form helicoidal layup sequences can decrease the dimensionless bending deflection of laminated plates by more than 5% compared with the quasi-isotropic plate and enhance the out-of-plane bending characteristics of CFRPC laminated plates effectively. The boundary conditions can significantly influence the nonlinear bending responses of helicoidal CFRPC laminated plates.

A novel damage evaluation of CFRPs under mode-I loading by using multi-instrument structural health monitoring methods

Mode-I fracture toughness test provides valuable information in the thickness direction of fiber reinforced polymer matrix composites. However, damage propagation under mode-I loading is dependent on the configuration of reinforcing material of the laminate. Understanding the damage types and their growth rate in mode-I fracture toughness test is a vital factor to obtain material allowable for safe design. In this study, mode-I tests are conducted on unidirectional, and twill woven carbon fiber reinforced polymer composite laminates. A new approach is proposed to interpret passive infrared thermography results based on correlating acoustic emission and thermography results in time whereby thermal activities can be classified into two main groups corresponding to matrix and fiber dominant failure types. It is demonstrated that matrix and fiber dominant failures lead to thermal activities with line-wise and point-wise form, respectively. Results show that four different damage types can be seen for mode-I fracture of both laminates. The temporal observations during thermoelastic cooling of the materials show that twill woven laminate releases relatively higher energies due to matrix dominant damage developments which means this configuration type is more prone for delamination failures.

Electrospun Polyvinylidene Fluoride Piezoelectric Fiber Glass/Carbon Hybrid Self-Sensing Composites for Structural Health Monitoring.

In this study, a polyvinylidene fluoride (PVDF)/graphene nanoplatelet (GNP) micro-nanocomposite membrane was fabricated through electrospinning technology and was employed in the fabrication of a fiber-reinforced polymer composite laminate. Some glass fibers were replaced with carbon fibers to serve as electrodes in the sensing layer, and the PVDF/GNP micro-nanocomposite membrane was embedded in the laminate to confer multifunctional piezoelectric self-sensing ability. The self-sensing composite laminate has both favorable mechanical properties and sensing ability. The effects of different concentrations of modified multiwalled carbon nanotubes (CNTs) and GNPs on the morphology of PVDF fibers and the β-phase content of the membrane were investigated. PVDF fibers containing 0.05% GNPs were the most stable and had the highest relative β-phase content; these fibers were embedded in glass fiber fabric to prepare the piezoelectric self-sensing composite laminate. To test the laminate's practical application, four-point bending and low-velocity impact tests were performed. The results revealed that when damage occurred during bending, the piezoelectric response changed, confirming that the piezoelectric self-sensing composite laminate has preliminary sensing performance. The low-velocity impact experiment revealed the effect of impact energy on sensing performance.

Assessment of two quasi-static approaches to mimic repeated impact response and damage behaviour of CFRP laminates

Full impact damage tolerance assessment requires the ability to properly mimic the repeated impact response and damage behaviour of composite materials using quasi-static approximations. To this aim, this paper reports an experimental investigation evaluating two quasi-static methods for mimicking repeated impact response and damage behaviour of Carbon Fibre Reinforced Polymer (CFRP) composite laminates. In this study, an 8.45-J single impact was repeated 225 times and mimicked with 225 times 6.51-J quasi-static (energy equivalent) indentations and with 225 quasi-static (force equivalent) indentations following the recorded impact peak force variation. Results show that the loading rate and the inertial effect are the two major factors affecting the responses of the composite laminates under out-of-plane concentrated loading. Both the energy- and force-equivalent quasi-static indentations failed to reproduce the impact responses greatly associated with high loading rate and inertial effect. The force-equivalent quasi-static indentations were performed in a semi-automatic way and induced damage states more similar to those of the repeated impacts than those of the energy-equivalent quasi-static indentations, whereas the latter can be better automated and has better reproducibility compared to that of the repeated impact responses, as it is less dependent on high loading rate and inertial effect.