Carbon Fiber Reinforced Plastics Composite Laminates Research Articles

Experimental and numerical studies of the open-hole compressive strength of thin-ply CFRP laminates

Thin prepregs with thickness of less than 0.06 mm support flexible lamination design because it is possible to apply various stacking sequences. The objective of this study is to elucidate the effects of the layer thickness and stacking sequence on the open-hole compressive (OHC) strength for thin-ply carbon fiber reinforced plastic composite (CFRP) laminates. Details of layer thickness and stacking sequence effects on the OHC strength for the thin-ply CFRP laminates were evaluated experimentally. Furthermore, finite element analyses incorporating Hashin’s 2-D failure criteria and a cohesive zone model were conducted to evaluate the damage progression behavior. Results demonstrated that the numerical model was useful for predicting the OHC strength of thin-ply CFRP laminates with various stacking sequences.

Novel orbital drilling and reaming tool for machining holes in carbon fiber–reinforced plastic (CFRP) composite laminates

Carbon fiber–reinforced plastics (CFRPs) have excellent mechanical and physical properties and are widely used to manufacture structural components and skins in aviation and aerospace. Industrial applications impose high requirements on the quality and efficiency of CFRP drilling. However, it is difficult to meet these requirements with conventional methods, such as drilling and orbital drilling. To improve hole processing quality, a novel cutting tool for orbital drilling was proposed in this research. Replacing the end mill in conventional orbital drilling (COD) with this novel cutting tool can enable an orbital drilling and reaming (ODR) machining process, which can suppress defects and reduce the thrust force when machining CFRP composite laminates. The thrust forces, tool wear, cutting temperatures, and hole quality in the ODR process presented in this paper were studied experimentally. The results indicated that machining with the novel ODR tool effectively reduced the thrust force and cutting temperature observed when machining with the general end mill. Moreover, the hole quality and tool life during ODR were exceedingly better than those during COD. The experimental results showed that processing with the novel tool has immense potential to replace existing processing methods for machining holes in CFRP composite laminates.

Terahertz scanning techniques for paint thickness on CFRP composite solid laminates

Terahertz ray (T-ray) scanning applications are promising tools. The use of T-ray for nondestructive evaluation was investigated on composite materials. In this characterization procedure, electromagnetic properties, such as the refractive index, were analyzed. The estimates of properties are in good agreement with known data. We successfully demonstrated the characteristics of T-ray propagating through Carbon fiber-reinforced plastic (CFRP) composites to acquire the refractive index by using the characterized material properties. A T-ray technique was developed for measuring paint thickness on CFRP laminates. Good results were obtained from tests performed on standard paint samples with thickness starting from approximately 100 μm. The method was based on reflection mode measurement with time of flight. Another method developed for measuring paint thickness using resonance frequencies was utilized to determine paint thickness on composite laminates. The paint thickness deduced from resonance frequencies agrees well with the result obtained directly from time-domain echoes.

Enhancing the thermal conductivity of carbon fiber reinforced polymer composite laminates by coating highly oriented graphite films

This paper focus on utilizing a simple and effective method that is coating highly oriented graphite films (HOGFs) on the surface of polyacrylonitrile-based (PAN-based) carbon fiber reinforced plastic (CFRP) composite laminates to improve the in-plane thermal conductivity of composite laminates. The thermal physical and mechanical properties of HOGF reinforced CFRP (HOGF-CFRP) composite laminates are measured. The measurement results show that HOGF greatly improves the in-plane thermal conductivity of hybrid HOGF-CFRP composite laminates. In-plane thermal conductivity of HOGF-T700/epoxy composite laminates increases to 50.7W/mK and enhances 14.1 times than that of T700/epoxy composite laminates. The in-plane thermal conductivity of HOGF-M55J/epoxy hybrid composite laminates is also up to 118.8W/mK and attains to the level of the aluminum alloys (nearly 120W/mK), which satisfy the requirement of engineering application in aircraft, aerospace and other high-end heat dissipation fields. Moreover, HOGF-CFRP composite laminates show the same low thermal expansivity as CFRP composite laminates. The mechanical results suggest that the HOGF-CFRP composite laminates not only have high in-plane thermal conductivity but also high specific mechanical property.

Trace-based stiffness for a universal design of carbon-fiber reinforced composite structures

A novel invariant-based approach to describe stiffness and strength of carbon-fiber reinforced plastic (CFRP) composites has recently been proposed in the literature. The approach is based on the trace of the plane stress stiffness matrix as a material property. The proposed method allows predicting strength and stiffness of the CFRP composite laminates within 1.5% error using [0] ply test only. The current study evaluates the use of the trace-based approach to set up a universal stress–strain relation among various materials and orthotropic laminates for composite structural components. One such stress–strain relation was evaluated for many CFRP composites using a beam subjected to in-plane and flexural loads. The current approach using the trace was found to be simple and accurate in the optimal design of composite structures once a geometric profile is defined by an isotropic material such as aluminum. Weight savings of composite laminates and structural components with various material and orthotropy combinations over aluminum can simply be determined with the current approach.

Machinability of drilling T700/LT-03A carbon fiber reinforced plastic (CFRP) composite laminates using candle stick drill and multi-facet drill

Carbon Fiber Reinforced Plastic (CFRP) composite laminates are widely used in aerospace and aircraft structural components due to their superior properties. However, they are regarded as difficult-to-cut materials because of bad surface quality and low productivity. Drilling is the most common hole making process for CFRP composite laminates and drilling induced delamination damage usually occurs severely at the exit side of drilling holes, which strongly deteriorate holes quality. In this work, the candle stick drill and multi-facet drill are employed to evaluate the machinability of drilling T700/LT-03A CFRP composite laminates in terms of thrust force, delamination, holes diameter and holes surface roughness. S/N ratio is used to characterize the thrust force while an ellipse-shaped delamination model is established to quantitatively analyze the delamination. The best combination of drilling parameters are determined by full consideration of S/N ratios of thrust force and the delamination. The results indicate that candle stick drill will induce the unexpected ellipse-shaped delamination even at its best drilling parameters of spindle speed of 10,000 rpm and feed rate of 0.004 mm/tooth. However, the multi-facet drill cutting at the relative lower feed rate of 0.004 mm/tooth and lower spindle speed of 6000 rpm can effectively prevent the delamination. Comprehensively, holes quality obtained by multi-facet drill is much more superior to those obtained by candle stick drill.

Effect of Surface Play on the Quality of the Hole when Drilling Multi-Directional CFRP Composites

The effect of surface ply on the quality of the hole produced when drilling multi-directional carbon fiber reinforced plastic (CFRP) composite laminates was investigated. A series of drilling experiments are performed using a carbide drill tool on two multi-directional CFRP composite laminates. The two composite laminates have similar stacking sequence except the surface plies, namely woven fabric and fiberglass scrim. The thrust force and torque was collected during the drilling process. The quality of the drilled hole was examined through surface roughness measurement, fiber pull out, and delamination. Thrust force was found to be higher for the composite laminate with woven fabric surface plies. The exit delamination factor measured from the holes with woven fabric surface plies found to be lower than the holes with fiberglass scrim surface plies.

Effect of Cutting Revolution Speed on Cutting Temperature in Helical Milling of CFRP Composite Laminates

CFRP (Carbon Fiber Reinforced Plastics) has higher specific strength, modulus of elasticity and so on. In the application for aviation industries, CFRP are remarkably used for many parts of airplane structures. It will be also widely applied for automobile parts in the future. CFRP is, however, well known as difficult-to-cut material which has very strong physical and mechanical characteristics. Drilling technique of CFRP which is one of the most important cutting operations is currently carried out in industrial factories. These manufactured parts have containing many precision holes for various purposes such as rivet holes. There are many typical problems in the precision drilling processes of CFRP plates which are burrs, chippings and delamination of composite materials, rapid wear of drilling tools and so on In our researches, it is found that drilled holes on CFRP plate by ball-nose end mill have good quality without any defections. By using the helical method with cemented-carbide ball end mill, high quality holes on the CFRP plates are obtained without burrs, chippings, and so on. However, cutting heat have negative effect on the strength of CFRP when it transcend heatresistant temperature of epoxy resin. In these researches, it is considered that the effect of the revolution speed to cutting heat on helical cutting of CFRP plates to improve the cutting processes. It is found that the cutting heat become lower by increasing revolution speed. Besides, because of shortening the cutting time, it is restrained the heat from transferring to the workpiece.

Pitch-catch ultrasonic study on unidirectional CFRP composite laminates using Rayleigh wave transducers

The importance of carbon fiber reinforced plastics (CFRP) has been generally recognized, and CFRP composite laminates have be- come widely used. Thus, a nondestructive technique would be very useful for evaluating CF/epoxy composite laminates. A pitch-catch UT signal is more sensitive than is a normal incidence backwall echo of a longitudinal wave in composites. The depth of the sampling volume where the pitch-catch UT signal came from is relatively shallow, but the depth can be increased by increasing the separation distance of the transmitting and receiving probes. Moreover, a method is utilized to determine the porosity content of a composite lay-up by processing micrograph images of the laminate. The porosity content of a composite structure is critical to the overall strength and performance of the structure. The image processing method developed utilizes software to process micrograph images of the test sample. The results from the image processing method are compared with existing data. Beam profile is characterized in unidirectional CFRP using pitch-catch Rayleigh probes. The one-sided and two-sided pitch-catch techniques are utilized to produce C-scan images with the aid of an automatic scanner. The pitch-catch ultrasonic signal corresponds with the simulated results of unidirectional CFRP composites.

Evaluation of drilling parameters on thrust force in drilling carbon fiber reinforced plastic (CFRP) composite laminates using compound core-special drills

Drilling is the mostly used secondary machining of the fiber reinforced composite laminates, while the delamination occurs frequently at the drill exit in the workpiece. In the industrial experiences, core drill shows better drilling quality than twist drill. However, chip removal is a troublesome problem when using the core drill. Conventional compound core-special drills (core-special drills and step-core-special drills) are designed to avoid the chip removal clog in drilling. But the cutting velocity ratio (relative motion) between outer drill and inner drill is null for conventional compound core-special drills. The current study develops a new device and to solve the problems of relative motion and chip removal between the outer and inner drills in drilling CFRP composite laminates. In addition, this study investigates the influence of drilling parameters (cutting velocity ratio, feed rate, stretch, inner drill type and inner drill diameter) on thrust force of compound core-special drills. An innovative device can be consulted in application of compound core-special drill in different industries in the future.

A Nondestructive Study on Fiber Layup and Porosity Level in CFRP Composite Laminates Using Ultrasonic Pitch-Catch Method

A nondestructive technique would be very useful for evaluating the CF/Epoxy composite laminates. It is found that a pitch-catch signal was more sensitive than normal incidence backwall echo of longitudinal wave to subtle flaw conditions in the composites (damages, fiber orientation, low level porosity, ply waviness, and cracks). The depth of the sampling volume where the pitch-catch signal came from was relatively shallow with the head-to-head miniature Rayleigh probes, but the depth can be increased by increasing the separation distance of the transmitting and receiving probes. Also, a method was utilized to determine the porosity content of a composite lay-up by processing micrograph images of the laminate. The porosity content of a composite structure is critical to the overall strength and performance of the structure. The image processing method developed utilizes a free software package to process micrograph images of the test sample. The results from the image processing method are compared with existing data. Beam profile was characterized in unidirectional CFRP (Carbon fiber reinforced plastics) with using pitch-catch Rayleigh probes and the one-sided and two-side pitch-catch technique was utilized to produce C-scan images with the aid of the automatic scanner. Also, it is confirmed that the pitch-catch ultrasonic signal was corresponding with simulated results assuming in unidirectional CFRP composites.

Feasibility on fiber orientation detection of unidirectional CFRP composite laminates using one-sided pitch–catch ultrasonic technique

It is important to assess fiber orientation, material properties and part defect because strength and stiffness of composites depend on fiber orientation of CFRP (carbon fiber reinforced plastics). A one-sided pitch–catch setup was used in the detection and evaluation of ultrasonic wave behavior and fiber orientation in the unidirectional CFRP composite laminates. Two Rayleigh wave transducers were joined head-to-head and used in the pitch–catch mode on the surface of the composites. The pitch–catch signal was found to be more sensitive than normal incidence backwall echo of longitudinal wave to subtle flaw conditions in the composite. Especially, one-sided ultrasonic measurement was made with using a Rayleigh wave transducers and the Rayleigh ultrasonic waves were extensively characterized in the CFRP composite laminates. Also, a conventional scanner was used in an immersion tank for extracting fiber orientation information in the unidirectional laminate. Therefore, it is thought that the proposed method is useful to evaluate integrity of CFRP laminates.

Seismic Rehabilitation of Reinforced Concrete Frame Interior Beam-Column Joints with FRP Composites

An experimental research program is described regarding the use of externally applied carbon fiber-reinforced plastic (CFRP) jackets for seismic rehabilitation of reinforced concrete interior beam-column joints, which were designed for gravity loads. The joints had steel reinforcement details that are known to be inadequate by current seismic codes in terms of joint shear capacity due to the absence of transverse steel hoops and bond capacity of beam bottom steel reinforcing bars at the joint. Lap splicing of beam bottom steel reinforcement at the joint using externally applied longitudinal CFRP composite laminates is investigated. Improvement of joint shear capacity using diagonal CFRP composite laminates is another strengthening scheme employed. Concrete crack widths for the as-built specimens and the extent of CFRP delamination for the rehabilitated specimens at various drift ratios are reported. The test results indicate that CFRP jackets are an effective rehabilitation measure for improving the seismic performance of existing beam-column joints with inadequate seismic details in terms of increased joint shear strength and inelastic rotation capacity. In addition, CFRP laminates are effective rehabilitation measures for overcoming problems associated with beam bottom steel bars that have inadequate embedment into the beam-column joints.

Ultrasonic Nondestructive Approach on Fiber Orientation Inspection in CFRP Composite Laminates

Owing to the advantages associated with their very large strength-to-weight and stiffnessto- weight ratios, composite materials are attractive for a wide range of applications. Increasingly, high performance engineering structures are being built with critical structural components made from composite materials. In particular, the importance of carbon-fiber reinforced plastics (CFRP) has been generally recognized in both space and civil aircraft industries, and CFRP composite laminates are widely used. It is very important to detect fiber orientation error in orthotropic composite laminates because the layup of a CFRP composite laminates affects the properties of the laminate, including stiffness, strength and thermal behavior. In this study, a new approach was investigated on detection of fiber orientation with using two longitudinal and a shear wave ultrasonic transducers for the orthotropic composite laminates. During testing, the most significant problem is that the couplant conditions do not remain the same because of changing the viscosity of the couplant. Therefore, making a design for generating shear wave with longitudinal transducers would greatly aid in alleviating the couplant problem. A pyramid with an isosceles triangle was made of aluminum in order to generate shear waves using two longitudinal transducers based on ultrasonic-polarized mechanism. It is found that the shear wave was very sensitive to fiber of CFRP composite. Finally, a CFRP composite material was nondestructively characterized in order to measure fiber orientation error area using automated data acquisition C-scan system.

Feasibility and Application on Ultrasonic-Polarized Shear Wave of Fiber Orientation Detection in Orthotropic Composite Laminates

It is very important to detect fiber orientation error in orthotropic composite laminates because the layup of a CFRP (carbon-fiber reinforced plastics) composite laminates affects the properties of the laminate, including stiffness, strength and thermal behavior. In this study, an investigation of shear wave ultrasonic technique was carried out in order to detect stacking orientation error for the orthotropic composite laminates. During testing, the most significant problem is that the couplant conditions do not remain the same because of changing the viscosity of the couplant. Therefore, the design and use of a shear wave transducers would greatly aid in alleviating the couplant problem. A pyramid with an isosceles triangle with two 45o was made of aluminum to generate shear waves using two longitudinal transducers based on ultrasonicpolarized mechanism. Also, the signal splitter was connected to the pulser jack on the pulser/receiver and to the longitudinal transducers which were mounted with mineral oil. The shear transducer was mounted on the bottom as a receiver with burnt honey. It is found that the shear wave was generated at a maximum and a minimum based on the ultrasonic-polarized mechanism. Finally, test results with model data were compared for a fiber orientation of the laminates.

Influence of stacking sequence on leakage characteristics through CFRP composite laminates

In this paper, gas leakage characteristics of damaged carbon fiber reinforced plastic (CFRP) laminates for three stacking sequences were obtained experimentally with the use of in-plane biaxial tests. Permeability through the laminates was measured under biaxial loadings, and the damages induced by mechanical loads were identified with using ultra-sonic C-scan to acquire relationships between damage and permeability. The results of the experiments imply that onset of leakage due to development of damage is dependent on stacking sequences, and permeability under tensile loadings is an increasing function of biaxial loads. From these findings, leakage characteristics would be dominated by crack density, leak path complexity which depends on stacking sequences, and crack opening displacements which attribute to thermal and mechanical loadings.

Ultrasonic Detection of Fiber Orientation in Composite Laminates for Use of Vehicular Structures

The layup of a CFRP (carbon-fiber reinforced plastics) composite laminates affects the properties of the laminate, including stiffness, strength and thermal behavior. It is very important to detect ply error before the laminate is cured for both manual procedure and fiber placement procedure. An ultrasonic technique would be very beneficial, which could be used to test the part after and before curing laminates and requires less time than the optical test. Also cross-polarized scan is very sensitive to the layup errors and ply misorientations. Scanners were set out for different measurement modalities for acquiring ultrasonic signals as a function of in-plane azimuthal angle. Firstly, a manual scanner was built for making transmission measurements using a pair of normal-incidence shear wave transducers to find the effect of fiber misorientations of composite laminates. Also a method for nondestructively determining the ply layup in a composite laminate is presented. The method employs a normal-incidence longitudinal ultrasound to perform C-scan of ply interfaces of the laminate. And a ply-by-ply vector decomposition model has been utilized for evaluating layup errors in composite laminates fabricated from unidirectional plies. Test results between after and before curing laminates with model data were compared for a fiber orientation of the laminates.