Polymer Matrix Composite Laminates Research Articles

Application of the size effect law to the determination of R-curves for transverse cracking in polymer matrix composite laminates using single edge notched bend specimens

The R-curves for transverse cracking could be determined based on the size effect law using SENB specimens, where the R-curves determined by the size effect law were consistent with those determined by the compliance method. The crack growth resistance in the steady-state and the crack extension at the onset of the steady-state of carbon-fiber/epoxy laminates, T800S/2592, were determined to be 0.22 N/mm and 0.36 mm, respectively. The crack growth stability in SENB specimens depended not only on the load control method but also on the specimen geometry, whereas a unique R-curve could be obtained regardless of the crack growth stability.

Ramie Fiber Woven Composite: The Effect of Feedrate Variation on the Tensile Strength of the Open Hole in the Drilling

Composite with woven ramie as reinforcement is a combination of woven from hemp plant fibers with resin adhesive (matrix) which each has different characteristics, which with the combination will produce a new material with better properties. The purpose of this study is to determine the magnitude of the influence of federate variations on the tensile strength of open holes in drilling, with the test method carried out with reference to ASTM D 5766/D 5766M-02 (Standard Test Method for Open Hole Tensile Strength of Polymer Matrix Composite Laminates). The tensile test speed used is 5 mm/minute. The data taken is the maximum tensile strength when the specimen breaks. The results of this study indicate that the change in feed rate affects the tensile strength of the ramie composite. The greater the feed rate used is in grading the ramie fiber composite, the smaller the composite tensile stress value becomes. In this study, the highest tensile strength is obtained from composites with a feed rate of 0.05 mm/rev and the lowest at a feed rate of 0.15 mm/rev. The change in spindle speed also affects the magnitude of the tensile strength in the ramie composite. As with the feed rate speed, the greater the spindle speed used to grind the composite, the lower the tensile strength of the composite. In this study, the maximum tensile strength value tends to be obtained by a composite with a spindle speed of 88 rpm and the lowest at a spindle speed of 1500 rpm. This study uses the type of chisel "brad and spur" with three kinds of diameter variations. The larger the diameter of the drill chisel used, the smaller the tensile strength of the composite obtained.

Effect of Scarf Repair Geometry on the Impact Performance of Aerospace Composites.

This experimental study investigates the effect of scarf geometry in restoring the impact response of scarf-patched 3 mm thick glass-fiber reinforced polymer (GFRP) matrix composite laminates. Traditional circular along with rounded rectangular scarf patch configurations are considered repair patches. Experimental measurements revealed that the temporal variations of force and energy response of the pristine specimen are close to that of circular repaired specimens. The predominant failure modes were witnessed only in the repair patch which includes matrix cracking, fiber fracture, and delamination, and no discontinuity in the adhesive interface was witnessed. When compared with the pristine samples, the top ply damage size of the circular repaired specimens are larger by 9.91%, while that of the rounded rectangular repaired specimens is larger by 434.23%. The results show that circular scarf repair is a more suitable choice of repair approach under the condition of a 37 J low-velocity impact event even though the global force-time response is similar.

Auxetic Composite Laminates with Through-Thickness Negative Poisson's Ratio for Mitigating Low Velocity Impact Damage: A Numerical Study.

Auxetic materials are those that exhibit negative Poisson’s ratios. Such a unique property was shown to improve the indentation and impact resistances. Angle-ply composite laminates can be designed to produce negative Poisson’s ratio at the laminate level due to the large anisotropicity of the individual layer and the strain mismatch between adjacent layers. This paper investigates the effect of through-thickness negative Poisson’s ratio on the low velocity impact behaviors of carbon fiber reinforced polymer matrix composite laminates, including the global impact behaviors, as well as the delamination, and the fiber and matrix damage. Results from numerical investigations show consistently reduced fiber and matrix tensile damage in the auxetic laminate in all plies, in comparison to the non-auxetic counterpart laminates (up to 40% on average). However, the auxetic laminate does not present a clear advantage on mitigating the delamination damage or the matrix compressive damage.

A Study on the In-Plane Shear-after-Impact Properties of CFRP Composite Laminates.

Impact loading on carbon fiber reinforced polymer matrix (CFRP) composite laminates can result in a significant reduction in their residual properties, and the (ShAI) properties of the composite material are essential to obtain the material allowable values of the shear dominated composite structures. In order to obtain the ShAI properties of the composite material in pure shear stress at a coupon level, this study presents theoretical, experimental, and numerical methods and analysis work on the in-plane shear and ShAI properties of the composite laminates. Theoretically, a method of sizing the composite specimen loading in shear is developed through comparing the load values due to buckling and the material failure. Following this, both impact tests using the drop-weight method and ShAI tests using the picture frame test method are conducted, and the influences of the impact energies on the impact damage and the residual ShAI values are evaluated. Moreover, a progressive failure finite element model based on the Hashin’s failure criterion and the cohesive zone model is developed, and a two-step dynamic analysis method is performed to simulate the failure process of the composite laminates under impact loading and ShAI loading. It is found that the impact damage with the cut-off energy, 50 J, causes a 26.8% reduction in the residual strength and the residual effective shear failure strain is about 0.0132. The primary reason of the shear failure is the propagation of both the matrix tensile failure and interlaminar delamination. It can be concluded that the proposed theoretical, experimental, and numerical methods are promising factors to study the ShAI properties of the composite materials.

Coupled thermo-mechanical modeling of drilling of multi-directional polymer matrix composite laminates

The influence of in-situ cutting temperature on machining induced damage and machining forces during drilling of multi-directional carbon fiber reinforced polymer (MD-CFRP) composites has been examined using a coupled thermo-mechanical finite element (FE) framework. The MD-CFRP laminate has been modeled ply-by-ply as an equivalent homogeneous anisotropic material (EHM) using temperature dependent laminate elastic and fracture properties. Stress-based criteria has been adopted for element deletion simulating the drilling process. The intralaminar damage model for simulating various composite machining induced damage modes was implemented in the FE framework via a user material subroutine. A new composite damage criterion is proposed that accounts for the out-of-plane drilling damage behavior along tool feed direction. Additionally, a fracture mechanics approach has been used to simulate interlaminar delamination onset using surface based cohesive elements at the drill exit plies. The current numerical model predictions show a good agreement with drilling experiments for thrust force, delamination damage, and in-situ cutting temperature.

Mitigation of notch sensitivity by controlled alignment of carbon nanotubes in epoxy using electric field application

A novel process design methodology for mitigating notch sensitivity in CNT/epoxy nanocomposite plates containing rectangular filleted notches has been presented in this work. Multi-wall carbon nanotubes (MW-CNTs) were selectively oriented in target zones around the notch using a controlled transient non-uniform electric field to alleviate stress concentration effects during tensile loading. The improvement in overall tensile strength of the notched nanocomposite plates with three different orientations (0°, 45° and 90°) with respect to the loading direction is demonstrated. A maximum improvement in tensile strength of ~ 55% in comparison to neat epoxy resin was observed in case of 45° notch orientation by employing this technique. Full-field strains obtained using digital image correlation (DIC) during testing provide a detailed look at the deformation progression around the notch. Fractography analysis was performed to identify the mechanisms in support of the observations made. This study has wide ranging applications to polymer matrix composite laminates with notches.

Ultrasonic inspection of hybrid polymer matrix composites

Polymer-matrix composite (PMC) materials used for a wide variety of engineering applications are often manufactured as hybrid carbon- and glass-fibre-reinforced laminates to exploit the respective properties of each material. From the exterior, hybrid PMCs are visually deceptively similar to monolithic laminates, but just as their mechanical, electrical and thermal properties differ, so their acoustic properties vary due to hybridisation. In this article, the mechanical and structural properties of hybrid PMC laminates pertinent to acoustic measurements and that affect sound propagation, such as: material density, stiffness, and laminate layup sequence, and their influence on ultrasonic defect detection, are explained via a detailed analysis of the ultrasonic waveforms, experimental inspection data, and analytical modelling.

Experimental and Numerical Validation of Unmanned Aerial Vehicle Structure Fabricated using Graphene based Polymer Matrix Composites

This paper describes the investigation of the polymer matrix composite laminate of epoxy resin systems and graphene oxide (GO) reinforced with glass fiber. The laminates of epoxy glass fiber reinforced with GO has been fabricated by hand layup method and the fabricated laminate is further cut into test specimens as per ASTM standards and tested for their strength and stiffness. As per the experimental studies, the strength to weight ratio is increased. An attempt has also been made to observe how the different volume addition (1.5%, 3%, 4.5% and 6%) of GO to epoxy matrix has affected the tensile strength, Young’s modulus and % elongation of the laminate made of composite. The outcome of the experimental characterization of the composites has encouraged further choosing epoxy / GO (1.5% by volume) towards fabricating a simplified version of UAV. Laminate code EPWM12, an epoxy / GO woven mat 12-layer composite, has the satisfying peak load carrying capacity as well as three-point flexural strength as opposed to other four materials considered in this study. The Monte Carlo simulation showed that likelihood of EPWM12 material being safe for UAV is 96%.

Experimental evaluation of mechanical properties of polymer matrix composites reinforced with date palm frond fibers from Oman

In this study, date palm fronds (DPF) were collected from Sultanate of Oman and treated with NaOH solution. Polymer matrix composite laminates reinforced with DPF fibers of different weight ratio were prepared using vacuum bagging technique. These laminates were subjected to several tests to study their mechanical properties like tensile strength, bending strength, impact strength and hardness. The optimum process parameters for producing the composites with improved mechanical properties were found out by employing the Taguchi method as optimization technique. The scanning electron microscopy (SEM) images of tensile test fractured specimens were studied to interpret the characteristics of DPF fibers.

Analytical model for determining effective stiffness and mechanical behavior of polymer matrix composite laminates using continuum damage mechanics

The present paper proposes a new analytical model for predicting the effective stiffness of composite laminates with fiber breaks and transverse cracks. The model is based on continuum damage mechanics and the classical laminate theory. We derived damage variables describing stiffness reduction due to fiber breaks and its maximum value during ultimate tensile failure from the global load-sharing model. Furthermore, a simplified analytical model is presented for obtaining two damage variables for a cracked ply subjected to transverse tensile loading or in-plane shear loading. This model was developed assuming that the displacement field of the longitudinal direction can be expressed in the form of a quadric function by loosening the boundary condition for the governing differential equation. For verifying the developed model, the elastic constants of damaged composite laminates were predicted for cross-ply and angle-ply laminates and compared with the finite element analysis results. As for the appropriate expression of the effective elastic stiffness matrix of the damaged ply, we verified four types of effective compliance/stiffness matrices including the Murakami, Yoshimura, Li, and Maimí models. We found the Maimí model to be the most appropriate among these four models. Moreover, we successfully simplified the expressions for damage variables in the complicated infinite series obtained in our previous study. We also proved that this could contribute toward improving the accuracy of our analysis. After verifying the present model, the stress–strain response and failure strength of carbon- or glass-fiber-reinforced plastic cross-ply laminates were predicted using Maimí’s compliance model and the simplified damage variables.

A three-dimensional stochastic progressive damage simulation model for polymer matrix-based laminate composites

This article proposes a three-dimensional (3D) stochastic progressive damage simulation model for the fiber-reinforced polymer matrix composite laminates. Constituents’ strength and fracture energy of each lamina were accounted as spatially varying random fields by 3D Karhunen–Loeve expansion method. Damage mechanisms modeled by continuum damage mechanics include internal damages of matrix and fiber. An anisotropic damage model was used for damage initiation and evolution of each lamina. By the proposed model, we investigated influences of variabilities in the lamina strength properties, and fracture energies along with delamination damage to the damage progression, strength, and post-failure behavior.

Mechanics of delamination-free drilling in polymer matrix composite laminates: A review

There is a critical limit of thrust force during drilling operation in a composite laminate below which no delamination takes place, which is known as the “critical thrust force”. In this paper, various critical thrust force models have been discussed in detail for circular- and elliptical-shaped delaminations around the drilled hole. Critical thrust force models for circular-shaped delamination for isotropic composite laminates and anisotropic composite laminates for different loadings like point load, uniformly distributed load, triangular load, and their combinations using different drill geometries have been discussed. With elliptical-shaped delamination, critical thrust force models for anisotropic composite laminates are discussed for: point load, uniformly distributed load, combined point plus distributed load, and point load for antisymmetric composite laminates. At several locations, graphs have been created to illustrate the dependence of various parameters on the critical thrust force. These graphs will be of use for practising engineers while selecting tool or/and machining parameters during drilling of polymer matrix composites. A tool designer can get good insight from these graphs while designing an optimal drilling tool. The paper highlights the importance of load distribution across the drill causing deflection leading to damage due to delamination in composite laminates. Special drill geometries help in better distribution of thrust forces towards periphery and improve the critical thrust force for the prevention of damage due to delamination during drilling in composite laminates.

Wear behaviour of hybrid polymer matrix composites using Taguchi technique

This work aims at developing new hybrid polymer matrix composites with epoxy resin as matrix material, kevlar, carbon and glass fibers as reinforcements. The fiber reinforced polymer matrix composite (FRP) laminates were prepared by hand layup method. The samples were prepared and tested by pin on disc wear tester for evaluating the wear properties, using Taguchi’s Design of Experiments approach – L9 Orthogonal Array. By increasing the thickness of hybrid polymer matrix composite laminate, which can be used in many applications in the automotive industry and in engineering structures, better wear properties have been achieved. Finally, from the experimentation, sample 3 sequence (CKCKC) has given lower wear rate than other samples.

Dynamic Instability Analysis of Multifunctional Composite Structures

A dynamic instability analysis of fiber reinforced composite cantilever beams has been carried out in this study. Both experimental and numerical studies are performed to estimate the flutter speeds. Three different types of composite beams [namely, glass fiber reinforced plastics, aluminum fiber reinforced (glass reinforced aluminum), and multifunctional carbon fiber reinforced composites] have been considered in the analysis. A graphite fiber reinforced polymer matrix composite laminate with dimensions of is used in the experiments. The fibers are oriented along 0 deg: that is, along the direction of major dimension of the laminate. The experiments are conducted on three such beams by clamping one end of the beam to a heavy steel frame and leaving the other end free. The natural frequencies, mode shapes, and structural damping characteristics of each beam are estimated using the modal analysis through the fast Fourier transform analyzer. Variation of the damping and the frequency with wind velocity for each beam is illustrated through the and plots. The modal assurance criterion is also verified. Experiments are further continued to perform a dynamic instability analysis by clamping the beam inside the test chamber of a low-speed suction-type wind tunnel. The beam response at various wind speeds is captured through an accelerometer mounted at the tip. Based on the experiments, the flutter speed of the tested beams is estimated to be around . A numerical analysis framework is developed using the ZAERO code to perform the modal and flutter analyses. Numerical results are compared to the experimental results and are found to be in excellent agreement. Therefore, the numerical framework has been further extended to carry out the flutter analysis of the multifunctional composite beams, such as glass reinforced aluminum and plastic lithium–ion battery embedded composite beams. The multifunctional laminated composite beams are observed to have better dynamic stability as compared to the glass fiber reinforced polymer composite beams.

Nanocellulose-coated carbon fibers towards developing hierarchical polymer matrix composites

In this research, 0.1, 0.25 and 0.5 wt% MFC aqueous suspensions were used to impregnate carbon fiber fabrics via aspersion and immersion routes to build a cost-effective hierarchical polymer matrix composite laminates with enhanced load carrying capacity. Mechanical performance improvements of 28 and 21% were obtained in terms of ultimate tensile strength for 0.1 wt% MFC suspension via aspersion and immersion routes, respectively. The same impregnation conditions provided increments in tensile toughness of 52 and 31%, respectively, showing the positive role of the nanostructure as a strong interfacial agent. MFC solution aspersion was determined as the best impregnation procedure towards strengthening and toughening of the final product.

Effect of fiber lay-up configuration on the electromagnetic interference shielding effectiveness of continuous carbon fiber polymer-matrix composite

Continuous carbon fiber polymer-matrix multifunctional structural composites capable of electromagnetic interference (EMI) shielding are needed for electronics and radiation sources. The laminate's fiber lay-up configuration affects the shielding effectiveness, as shown in this work for unmodified conventional carbon fiber polymer-matrix composite laminates with high-strength PAN-based carbon fiber and a polyamide thermoplastic matrix. The radiation is normal-incidence unpolarized plane wave, as commonly used. The shielding is dominated by absorption rather than reflection – more so for crossply composites than unidirectional composites. Due to the electrical conductivity longitudinal-to-transverse ratio of 930 for a lamina, the absorption-loss/thickness longitudinal-to-transverse ratio is 30 at 1.0 GHz. This factor of 30 means that the contribution of the fibers transverse to the electric field to absorption is negligible compared to that of the fibers parallel to the electric field. The ratio of absorption-loss/thickness for the crossply composite to that for the unidirectional composite with the same number of laminae is ∼4, and the ratio of the reflection loss for the crossply composite to that for the unidirectional composite is ∼2. The values of these ratios are consistent with electromagnetic theory for unpolarized radiation. This work strengthens the science base for the design of continuous fiber composites for shielding.

The effects of fiber orientation and adhesives on tensile properties of carbon fiber reinforced polymer matrix composite with embedded nickel-titanium shape memory alloys

Tensile tests of Nickel-titanium (NiTi) shape memory alloys (SMA) embedded within carbon fiber reinforced polymer matrix composite (CFRP/PMC) laminates were evaluated with simultaneous monitoring of modal acoustic emissions (MAE). Three different layup configurations utilizing two different thin film adhesives were applied to bond the materials. Ultimate tensile strengths, strains, and moduli were obtained along with cumulative AE energy of events and specimen failure location. Scanning electron microscopy was used to examine the break areas of the specimens post-test. Microscopy was used to validate failure locations revealed from MAE analysis. A unique finding within this research showed that 90° plies in the outer ply gave the strongest acoustic signals as well as the cleanest fracture of the specimens tested. Overlapping 0° ply layers surrounding the SMA was found to be the best scenario to prevent failure of the specimen itself.

Probabilistic strength based matrix crack evolution model in multi-directional composite laminates under fatigue loading

A model to predict the matrix crack evolution in multi-directional (MD) polymer matrix composite laminates under in-plane fatigue loading is presented in the current work. Unlike matrix crack evolution under static loading, the matrix cracks in off-axis plies do not form tunneling cracks under fatigue loading; rather, they initiate and grow with increasing load cycles. A probabilistic strength based criterion for matrix crack initiation in off-axis plies based on a Weibull distribution for in situ ply strength variation has been used. An oblique co-ordinate based shear lag analysis has been used to estimate the stresses in the cracked laminate. Smith Watson Topper (SWT) parameter has been used to model the number of cycles to initiate the first matrix crack, and log-normal probability distribution has been used to handle the scatter in crack initiation life. The matrix crack growth rate has been modeled using Paris law based on mixed mode effective stress intensity factor. Using the crack initiation curve and strength degradation based on Palmgren-Miner damage rule, new crack initiation has been simulated. Few parameters needed for the threshold stress intensity and saturation crack spacing have been identified from a reference stress data of cross-ply laminate. The crack density evolution has been simulated for cross-ply and MD-laminates under various constant amplitude in-plane fatigue stress levels. The matrix crack density evolution and its stiffness degradation predictions with the number of cycles have been compared with existing experimental values. A good correlation is found to exist between the experimental data and predictions for both cross-ply and MD-laminates.

Identification of failure modes of composite thin-ply laminates containing circular hole under tension by acoustic emission signals

Composite thin-ply laminates have been reported to exhibit superior performance in various loading conditions than standard-ply laminates due to positive size effects. However, the ultimate tensile strength of the thin-ply (<0.125 mm) laminates containing circular hole was lower than that of the thick (>0.125 mm) or standard-ply (0.125 mm) laminates with same size of the hole. Besides, fracture morphologies showed a transition from a combined mode of matrix crack, delamination and pull-out at 45° and −45° ply in the thick and standard-ply laminates to a quasi-brittle fracture in the thin-ply laminates. In order to explain the experimental phenomena, acoustic emission was used in this paper to identify and distinguish the failure modes of laminate specimens containing circular hole with different ply thickness, and finite element simulation was adopted to investigate the cause of lower tensile strength in the thin-ply specimen. Carbon fiber reinforced polymer matrix composite laminate specimens were prepared using prepregs with different ply thicknesses (0.02 mm, 0.055 mm and 0.125 mm). In tensile test, higher initial stress of damage, lower ultimate strength and quasi-brittle fracture morphology could be observed in the thin-ply laminate specimens with an open hole. The results of acoustic emission analysis demonstrated that the matrix damage and delamination were suppressed in the thin-ply laminates, and superior damage suppression and crack-propagating resistance in the thin-ply laminates lead to quasi-brittle fracture morphology. Besides the more homogeneous micro-structure and isotropic behavior of the thin-ply laminates leaded to higher initial damage stress compared to the laminates with thick plies. However, according to finite element analysis, the thin-ply laminates exhibited much stronger stress concentration after initial damage until ultimate failure of the specimens, leading to lower ultimate strength under tensile loading.