Composite Prepreg Research Articles

Axial crush and bending collapse of an aluminum/GFRP hybrid square tube and its energy absorption capability

In this paper, energy absorption capability of axial crush and bending collapse of aluminum/GFRP hybrid tubes were investigated. Glass fiber–epoxy composite prepregs were wrapped around an aluminum tube and then cured completely in the autoclave under the recommended cure cycle. Bonding process between composite and aluminum tubes was performed by excess resin extracted from the composite tube during curing process. For comparing energy absorption characteristics of the hybrid tube with those of pure aluminum and composite tubes, tests were performed using specimens made of an aluminum alloy and a composite material, respectively. Failure mechanisms of the hybrid tube under the axial compressive load and the bending load were experimentally investigated. For calculating energy absorption capability of axial crush and bending collapse behaviors of the hybrid tube, the modified plastic hinge collapse model and the modified Kecman's model for hybrid tube were suggested, respectively. Two suggested models for the hybrid tube showed a good agreement with the experimental results.

Investigation of prepreg bonded composite single lap joint

Adhesive bonded single lap joint has been used extensively in laminated composite structures. Using neat resin adhesives, however, the joint strength is comparatively low and the fabrication time is long. In order to increase the joint strength and reduce the fabrication time, two types of fiber pre-impregnated (prepreg) composites were used to bond composite single lap joints. Test specimens were prepared per ASTM D 3165-95 standard. Ninety days of accelerated conditioning using seawater and ultraviolet radiation were conducted to investigate the long-term performance of prepreg bonded single-lap joint in an offshore environment. The shear strength of various specimens was obtained using tension tests. Two types of neat resin bonded specimens were also used for comparisons. Finite element analysis was implemented to justify test results. Parameters affecting the load carrying capacity of prepreg bonded composite single lap joints were investigated based on finite element analysis results.

A method for the direct measurement of the fibre bed compaction curve of composite prepregs

A method to measure the fibre bed compaction curve directly from composite prepreg is presented. The method was used to measure the compaction curve of unidirectional and quasi-isotropic AS4/3501-6 carbon–epoxy prepregs. Similar compaction curves were obtained in all cases. The compaction curve obtained was used by a finite element process model, COMPRO, to simulate the uniaxial compaction of 8 and 16 ply laminates at different temperatures. The force–displacement response predicted by the model closely matched the experimental results. The method which can be used on both tape and fabric prepregs, has the major advantages of being a direct measure of the prepreg behaviour, and requires no special preparation of the sample.

Polypropylene-phenol formaldehyde-based compatibilizers. II. Application in PP/PA6 75/25 (wt/wt) blends : Borve, K. Larsen, Kotlar, H.K., Gustafxon, C.-G., Norwegian Institute of Science and Technology, Trondheim, Norway in journal of applied polymer science, vol 75, issue 3, 2000

Milled phenol–formaldehyde glass-fibre scrap (prepreg) was mixed with polypropylene (PP) and polyamide-6 (PA6). The oxidation induction time (OIT) of PP/prepreg composite measured by both chemiluminescence (CL) and Differential Scanning Calorimetry (DSC) was significantly longer than the oxidation induction time of unstabilised base PP. In addition, mechanical testing showed that the prepreg filler stabilised both PP and PA6 towards oxidation during long-term accelerated ageing. Headspace-gas chromatography/mass spectrometry (HS-GC/MS) showed that PP/prepreg composites emit somewhat larger amounts of volatile compounds compared to the reference PP/glass fibre composites, while the amount of volatile components emitted from PA6/prepreg composites was similar to the reference PA6/glass fibre composites. The new prepreg composites could have potential in thermally demanding applications especially if a secondary phosphite stabiliser is added to further increase the oxidative stability through synergy effects.

Prediction of the Tensile Load Capability of Co-Cured Steel-Composite Tubular Single Lap Joints Considering Thermal Degradation

Co-cured joints composed of composite and steel structures are realized by the excess resin extracted during cure of composite prepreg and the coupling pressure due to residual thermal stresses generated by the difference of coefficients of thermal expansion between the two materials. Although the excess resin from the composite prepreg is less dependent on the environmental temperature compared to conventional epoxy adhesives in which rubber is added to strengthen toughness, the coupling pressure is much dependent on the environmental temperature. In this study, the tensile load capability of co-cured joints composed of carbon fiber epoxy composite and steel adherends was experimentally investigated with respect to the stacking sequence of the composite and the environmental temperature. Also, the stress distributions in the composite were calculated by finite element method, from which the failure index of the composite adherend was calculated considering thermal degradation of the composite. The co-cured steel-composite tubular single lap joint under tensile loads might be applied to hybrid structures such as golf clubs and automotive composite propeller shafts which have a conventional adhesively-bonded joint by epoxy adhesives with fillers between a carbon/epoxy shaft and a metal shaft.

Processing and properties of solution impregnated carbon fiber reinforced polyethersulfone composites

AbstractCarbon fiber reinforced polymer composites are attractive because of their high stiffness and strength‐to‐weight ratios. In order to fully utilize the stiffness and strength of the reinforcement fiber, it is necessary to bring the polymer matrix and the reinforcement fiber together with homogeneous wetting. In this paper, a solution processing technique and the mechanical properties of carbon fiber reinforced polyethersulfone composites were investigated. The polymer was dissolved in cyclopentanone and fed onto a continuous carbon fiber tow using a drum winder. The solution‐processed composite prepregs were then layed up and compression molded into unidirectional composite panels for evaluation. The composite samples showed uniform fiber distribution and reasonably good wetting. The longitudinal flexural modulus was as high as 137 GPa, and longitudinal flexural strength 1400 MPa. In addition, the effects of polymer grade and processing conditions on the mechanical properties of the composites were discussed. It is suggested that the transverse properties and interlaminar fracture toughness could benefit from higher polymer matrix molecular weight. A careful design in the spatial distribution of the molecular weight would be necessary for practical applications.

Prediction of the Tensile Load Capability of Co-cured Steel-Composite Tubular Single Lap Joints Considering Thermal Degradation

Co-cured joints composed of composite and steel structures are realized by the excess resin extracted during cure of composite prepreg and the coupling pressure due to residual thermal stresses generated by the difference of coefficients of thermal expansion between the two materials. Although the excess resin from the composite prepreg is less dependent on the environmental temperature compared to conventional epoxy adhesives in which rubber is added to strengthen toughness, the coupling pressure is much dependent on the environmental temperature. In this study, the tensile load capability of co-cured joints composed of carbon fiber epoxy composite and steel adherends was experimentally investigated with respect to the stacking sequence of the composite and the environmental temperature. Also, the stress distributions in the composite were calculated by finite element method, from which the failure index of the composite adherend was calculated considering thermal degradation of the composite. The co-cured steel-composite tubular single lap joint under tensile loads might be applied to hybrid structures such as golf clubs and automotive composite propeller shafts which have a conventional adhesively-bonded joint by epoxy adhesives with fillers between a carbon/epoxy shaft and a metal shaft.

Long-range effects of carbon fiber on crystallization of semicrystalline thermoplastics

Non-isothermal crystallization of carbon fiber reinforced polyetheretherketone composites was studied with differential scanning calorimetry and Fourier transform infrared spectroscopy. Composite prepregs prepared by a solution pre-impregnation method with the matrix of different molecular weights were employed in the present work as the main model materials. Analyses of the different dependencies of non-isothermal crystallization on melt residual time in these systems revealed that carbon fibers had long-range effects on bulk crystallization of matrix polymer, which is rooted in the fact that the fibers tend to promote strain-induced nucleation in polymer. Comparison of the crystallization behavior of prepregs with that of the composite laminates indicated the importance of wetting and absorption to the effects of fiber on matrix crystallization, coinciding with the mechanism that short-range interaction formed the boundary to the flow under thermal stress.

Synthesis and Characterization of Short Carbon Fibre-Reinforced PMR-Type Polyimide Composites

Short carbon fibre-reinforced polyimide composites were prepared by wet impregnating chopped short carbon fibres with PMR-type polyimide matrix resin solution followed by evaporating the solvent with strong stirring. The processing properties of the prepolymer moulding powders were investigated. The mechanical properties and thermo-oxidative stability of the fabricated composite were also studied. Experimental results demonstrate that the short fibre filled moulding powders exhibit good melt resin flowing characteristics and can be processed by a hot press moulding technique to produce small-size, complicated composite structures which are difficult to produce using continuous fibre-reinforced composite prepregs by an autoclave technique. The composites exhibit outstanding mechanical properties and excellent thermal and thermo-oxidative stabilities at temperatures as high as 320 °C.

Mechanical properties of long-fibre thermoplastic composites with laser drilled microperforations: 1. Effect of perforations in consolidated material

A study is presented concerning a novel technique for enhancing the formability of long-fibre thermoplastic composites. A laser beam has been used to drill arrays of holes into PEEK/AS-4 and PPS/AS-4 carbon-fibre composite pre-preg. These arrays were designed to cut all the fibres to pre-determined lengths. Holes were of the order of 150 μm in diameter, with average fibre length reduced to either 20, 50 or 100 mm. Once perforated, the pre-preg material was consolidated into laminates in an autoclave. Tensile testing has been used to evaluate the effects of the laser drilling. Experimental data show that the perforation process does not affect the stiffness, but strength is reduced somewhat. This reduction is dependent on the distribution of holes and the nature of the laminate. The strength of notched laminates was found to be unaffected by perforation. Off-axis testing has been used to evaluate the transverse and shear strength of both PEEK- and PPS-based composites, and this has been linked to observed failure mechanisms. Finite element modelling has been used to confirm that shear failure parallel to the fibres is initiated by the stress concentrating effect of the perforations.

Cutting Behavior of Composite Prepregs

Two types of composite prepregs were selected to conduct experimental study on cutting. Both were cut in different conditions to investigate the fiber deflection of prepregs due to cutting. Also, the effect of cutting parameters on the strength of laminates made of cut prepregs was investigated. For unidirectional prepreg cutting, factors such as primary knife angle a, knife sharpness and relative orientation between cutting direction and fiber direction 6 have significant effect on fiber deflection. The firmness of backing plates is not an important factor. The fiber deflection of unidirectional prepreg due to cutting is not large enough to have significant effect on the strength of coupons made from these prepregs. For woven prepreg cutting, the fiber deflection is large and has some effect on the strength of coupons.

Torque Capacity of Co-Cured Tubular Lap Joints

The co-cured joint is an efficient joining technique because both curing and joining for composite structures are achieved simultaneously. In this paper, the torque capacities of the co-cured tubular lap joint with and without knurling of the pyramid type were experimentally measured. From the experiment, it was found that the excess resin of composite prepreg should not be extracted much because the excess resin played a role as an adhesive in the co-cured tubular lap joint whose steel adherends were not knurled. Also, it was found that the torque capacity of the co-cured joint was increased as the knurling size of the pyramid type on the surface of the steel adherend was increased.

Electrical sensing of shelf-cure properties of polymeric prepreg materials

Most polymeric thermoset materials change (cure) slowly as they lie in storage; a prime example of this is composite prepreg materials. These changes are generally vitrification, and are not readily observable using some of the standard cure-monitoring methods, such as DSC and FTIR, which sense mainly the gelation process. Evidence of this observation is presented, along with the successful results of an effort to monitor this shelf-cure process using a simplified resistivity meter.

Electrical sensing of shelf‐cure properties of polymeric prepreg materials

Most polymeric thermoset materials change (cure) slowly as they lie in storage; a prime example of this is composite prepreg materials. These changes are generally vitrification, and are not readily observable using some of the standard cure-monitoring methods, such as DSC and FTIR, which sense mainly the gelation process. Evidence of this observation is presented, along with the successful results of an effort to monitor this shelf-cure process using a simplified resistivity meter. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 337–342, 1997

The effect of adhesive bonding between aluminum and composite prepreg on the mechanical properties of carbon-fiber-reinforced metal laminates

The role of adhesion between aluminum sheets and fiber composite prepreg on the mechanical property profiles of carbon-fiber-reinforced metal laminates (CFRMLs) has been investigated. Differences in adhesive bonding were achieved by using two different aluminum surface treatments, one with a standard P2-Etch procedure and another with a modified FPL-Etch procedure with the subsequent application of a silane coupling agent. Double-cantilever beam (DCB) tests were conducted to measure the interfacial fracture energy, and an increase in interfacial fracture toughness by up to six times was achieved by using the latter method. Optical and scanning electron microscopy were used to study the failure behavior and fracture mechanisms of the CFRMLs. No clear differences were found in laminate mechanical properties such as tensile strength and Young's modulus. A reduction of 10% in the relative value for the interlaminar shear strength (ILSS) was observed for the laminate with poor interfacial adhesion associated with the P2-Etch method, in both three- and five-point bend tests. However, the residual strength of the notched CFRMLs is, in general, almost independent of the adhesion status between aluminum sheets and composite prepreg, although a slight increase in residual strength for laminates with weak interfacial adhesion was observed in the presence of small holes, because of the difference in delamination growth.

Cure Monitoring of Aerospace Epoxy Resins and Prepregs by Fourier Transform Infrared Emission Spectroscopy

Spectral analysis of the infrared radiation emitted from thin films of resin transferred from the surface of high performance aerospace carbon fibreepoxy composite prepregs and heated to the cure temperature allows the cure chemistry and kinetics to be monitored in real time. Quantitative spectra with excellent signal-to-noise ratio are obtained by heating a thin resin film on a platinum hotplate fitted to the external optics of a Fourier transform infrared (FTIR) spectrometer and referencing the resulting emission (with the platinum emission subtracted) to a graphite black body at the same temperature. The resulting spectra are identical to absorption spectra and the quantitative features of the analysis are demonstrated by the appearance of isosbestic points during the curing reactions, so indicating that concentration profiles of the reacting species may be obtained. From the initial rate of amine and epoxy consumption, activation energies of 75kJ mol−1 were obtained for both functional groups in the uncatalysed resin 4,4′-tetraglycidyl diamino diphenyl methane (TGDDM) with 27% 4,4′-diaminodiphenylsulfone (DDS), while values of 74 and 89kJ mol−1 were obtained for amine and epoxy consumption from the TGDDM/DDS prepreg catalysed with boron trifluoride monoethylamine (Hercules 3501–6), consistent with homopolymerization occurring in the prepreg as well as amine–epoxy addition. Analysis of the FTIR emission at 177°C of resin from prepreg aged up to 90h at 23°C and 55% relative humidity shows a lowering of epoxy and amine concentration and a higher rate of cure, consistent with the formation of catalytic species. This technique may be used to monitor changes in surface properties such as tack and resin transfer, in addition to changes in the cure profile of the aged epoxy propreg.

Flexural Properties of Unidirectional Composites Laminarily Reinforced with Mesophase Pitch Based Carbon Fibers and Alumina Fibers.

Unidirectional multistack composites of two kinds of composite prepregs, mesophase pitch-based carbon fibers (MCF)/epoxy and alumina fibers (ALF)/epoxy, were prepared. Since MCF has higher modulus and smaller tensile elongation than polyacrylonitrile-based carbon fiber (PCF), the flexural strength and modulus of the multistack composites were found to be different from the similar composites prepared by combination of PCF and ALF. In the interply-type MCF/ALF multistack composites which have the AFL perpregs in the center, fracture began in the top layer (compression side) with the bending load decreasing. In the composites having MCF prepregs in the center, small cracks were formed in the MCF layer with a slight yielding of the bending load. Since the fracture was slowed down and even stopped by the hybrid lamination, abrupt destruction of the whole composite was successfully suppressed. The modulus of the composites, which could be elucidated by the lamination beam theory, increased with increasing number of MCF layers and was much higher than that of PCF/ALF multistack composites.

High temperature hybrid titanium composite laminates: An early analytical assessment

This paper presents a new type of material system that shows great promise for aerospace applications. The concept consists of thin sheets of titanium bonded together with a polymer composite prepreg consisting of a high temperature resin reinforced with high or intermediate modulus fibers. The potential material performance is outstanding in terms of in-plane fatigue and fracture. As with all composite materials, the exact moduli and strength can be optimized for a given application by varying the constituents, their volume fractions and, in the case of the reinforcing fibers, their orientation. The paper includes analytical studies as well as experimental results.

5395648 Ceramic-ceramic composite prepregs and methods for their use and preparation

5395648 Ceramic-ceramic composite prepregs and methods for their use and preparation

Predicting Scaling Effect on the Notched Strength of Prepreg and Fiber Tow-Placed Laminated Composites

The effect of scaling on the notched strength and response of composite plates was investigated. Unidirectional prepreg and tow-placed laminated composites, both of which were made of the same fibers and resin system, were considered. In order to predict the scaling effect, the local damage accumulative inside the notched composites was considered. A finite element analysis based on an accumulative damage model previously proposed was developed for analyzing the response and tensile failure of composite laminates containing a slit or a circular hole of various sizes. The model consists of a constitutive equation which relates the damaged material to an accumulated damage state; and damage accumulation criteria which predict the state of damage as a function of the applied stresses. The free-edge induced damage was not considered in the model. The effect of scaling on the notched strength of laminated composites was evaluated by comparing the results of the calculations from the analysis with the test data generated at Stanford University and the Boeing Company. The predictions agreed with the test data very well for the notch sizes ranging from as small as 0.25 inch up to 2.5 inches. It was found that the larger the notch size, the more accumulated damage was predicted. Hence, the scaling effect on the notched composite strength is strongly related to the extent of damage accumulated inside the composites. The model also shows that the fiber interaction zone affects significantly the residual strength of notched composites. The higher fiber interaction zone tends to reduce fiber tensile strength, but to increase tensile notched strength. With the same material system, although the fiber tensile strength of unidirectional tow-placed composites was lower than prepreg composites, tow-placed composites exhibited higher notched strength than did the prepreg composites.