Bismaleimide Composites Research Articles

The Effect of Lightning Strikes on Bismaleimide Composites by Dynamic Mechanical Analysis

In this paper, a new method that has shown significant potential to characterize lightning strikes damage which is couple with dynamic mechanical analysis. The composite samples used in this work are based on carbon fiber/bismaleimide system. The analysis of the dynamic mechanical data demonstrate the glass transition temperature of the composites increased as a function of increasing lightning current , simultaneity with the presence ofpotential damage, whichare result in higher network cross-link density and the incipent degradation of the polymer matrix.

Experiment Research of Environment Effects on Fatigue Life of Carbon/Bismaleimide Composite Laminates with Central Hole

The effects of humidity and ultraviolet radiation aging on fatigue properties of carbon/ bismaleimide composites and coating protection action were presented. Specimens with central hole are made of carbon/bismaleimide laminates. Compression-compression (C-C) fatigue tests under normal lab environment were operated respectively for four groups of specimen, (1) specimen under normal lab environment, (2) specimen under UV radiation aging with dryness, (3) specimen under UV radiation aging with moisture, and (4) specimen with coating under UV radiation aging with moisture. Variance analysis of experimental outcomes gave significances of the environment effects on C-C fatigue life of specimens. The results reveal that UV radiation have remarkable effects on the C-C fatigue life of the composite laminates under the same humidity, whereas combined action of UV radiation (300MJ/ m2) and humidity have no significant effects on the C-C fatigue life. Coating can provide effective protect the specimen from UV radiation aging.

Thermal, morphological, and mechanical characterization of novel carbon nanofiber‐filled bismaleimide composites

AbstractNovel carbon nanofiber (CNF) ‐filled bismalemide composites were fabricated by a thermokinetic mixing method. The thermal and mechanical properties of composites containing 1 wt % and 2 wt % CNFs were investigated. Thermogravimetric analysis demonstrated that minimal improvement in thermal stability of the nanocomposites was obtained by the addition of CNFs. Dynamic mechanical analysis showed an increase in storage modulus (E′) and glass transition temperature (Tg) upon incorporation of nanofibers. Limiting oxygen index (LOI) has also been found to increase with incorporation of CNFs. Morphological studies of fractured surfaces of the composites has been carried out by scanning electron microscopy to determine the effect of fiber content and dispersion on the failure mechanism. In general, good dispersion was observed, along with agglomeration at some points and some fiber matrix interfacial debonding. A decrease in mechanical strength has been observed and debonding was found as the main failure mechanism. Further research outlook is also presented. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Accelerated ageing versus realistic ageing in aerospace composite materials. III. The chemistry of thermal ageing in bismaleimide based composites

AbstractSamples of two Aerospace grade bismaleimide composites (Cytec Fiberite 5250‐4/IM7 and 5250‐4/RTM) were subject to long‐term (≈ 1‐year) thermal ageing in air at temperatures of 70, 120, 170, 200, and 250°C. The changes to the chemical and physicochemical structure of the composite were then analyzed by a range of different techniques, including gravimetric analysis, Fourier Transform infrared spectroscopy, and dynamic mechanical analysis, to compare the effects of the different ageing temperatures and to see if much simpler and more fundamental testing techniques could provide more informative forecasting information than the standard mechanical testing methods. The results emphasize the strong variation in chemistry that takes place between the surface and the interior of the composite materials at all temperatures tested. The results also confirmed the significant variations in chemical and physicochemical ageing mechanisms (e.g. glass transition temperature, Tg) that occur between the more realistic ageing temperatures encountered “in service” (∼ 120°C) and the accelerated ageing conditions often used for ageing studies (>170°C). This article highlights the lack of agreement in scientific literature on the basic chemistry of bismaleimide cure. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007

Thermal properties and water sorption behaviors of epoxy and bismaleimide composites

In this work, we prepared epoxy/BMI composites by usingN,N′-bismaleimide-4,4′-diphenylmethane (BMI), epoxy resin (diglycidyl ether of bisphenol-A (DGEBA)), and 4,4’-diamino diphenyl methane (DDM). The thermal properties and water sorption behaviors of the epoxy and BMI composites were investigated. For the epoxy/ BMI composites, the glass transition and decomposition temperatures both increased with increasing BMI addition, which indicates the effect of BMI addition on improved thermal stability. The water sorption behaviors were gravimetrically measured as a function of humidity, temperature, and composition. The diffusion coefficient and water uptake decreased and the activation energy for water diffusion increased with increasing BMI content, indicating that the water sorption in epoxy resin, which causes reliability problems in electronic devices, can be diminished by BMI addition. The water sorption behaviors in the epoxy/BMI composites were interpreted in terms of their chemical and morphological structures.

Mechanical performance of hybrid bismaleimide composites reinforced with three-dimensional braided carbon and Kevlar fabrics

Abstract Short, unidirectional and laminated hybrid composites have been extensively investigated. However, very limited work has been conducted on three-dimensional (3-D) braided hybrid composites. In this work, 3-D braided carbon and Kevlar fibres were hybridized to reinforce a bismaleimide (BMI) resin. The purpose of this paper was to investigate the effect of carbon to Kevlar ratio on such mechanical properties as load–displacement behaviour, flexural strength and modulus, shear strength, and impact properties. The effect of surface treatment of hybrid fabrics on the flexural properties was also determined. Experimental results showed that the flexural strength and modulus of the 3-D braided carbon/Kevlar/BMI composites increased with relative carbon fibre loading up to a carbon to Kevlar ratio of 3:2 and then dropped. Positive hybrid effects were observed for both flexural strength and modulus. The results presented in this work proved that hybridization with certain amount of ductile Kevlar fibre markedly promoted the shear strength, impact energy absorption characteristics and damage tolerance of the all-carbon composite, which is of importance for the 3-D braided composites to be used in bone fixations. Fracture surfaces and microstructures of various 3-D braided hybrid composites were analyzed to interpret the experimental findings.

Interphase sizing temperature effect of LaRC PETI-5 on the dynamic mechanical thermal properties of carbon fiber/BMI composites

The dynamic mechanical thermal properties of carbon fiber-reinforced bismaleimide (BMI) composites processed using polyacrylonitrile(PAN)-based carbon fibers unsized and sized with LaRC PETI-5 amic acid oligomer as interphase material at 150°C, 250°C, and 350°C were investigated by means of dynamic mechanical thermal analysis. It was found that the storage modulus, loss modulus, tan δ and the peak temperature significantly depend on the sizing temperature as well as on the presence and absence of LaRC PETI-5 sizing interphase. The result showed that the carbon fiber/BMI composite sized at 150°C had the highest storage modulus at a measuring temperature of 250°C. The storage modulus decreased with increasing sizing temperature from 150°C to 350°C, being influenced by interdiffusion and co-reaction between the LaRC PETI-5 interphase and the BMI matrix resin. The present result is quite consistent with the interfacial result reported earlier in term of interfacial shear strength and interlaminar shear strength of carbon fiber/BMI composites. It is addressed that in the present composite system the sizing temperature of LaRC PETI-5 interphase critically influences not only the interfacial properties but also the dynamic mechanical thermal properties and its control is also important.

Aluminum‐borate‐whiskers‐reinforced bismaleimide composites. 1: preparation and properties

AbstractAluminum‐borate‐whiskers‐reinforced bismaleimide (BMI/Al18B4O33) composites were prepared, and the mechanical and thermal properties were investigated. Results show that the coupling agent used for surface treatment of whiskers has a great effect on the properties of these materials. Composites containing surface‐untreated whiskers, or silane‐compound‐KH 921‐treated whiskers, exhibited initially only a slight increase in the flexural strength when the whiskers weight content increased up to 5 wt%; thereafter, they showed a sharp decrease when the whiskers content was higher than 5 wt%. On the other hand, impact strength tests showed that the addition of the two kinds of whiskers decreased the impact strength of the composites. However, studies of the composite containing borate (BE4)‐treated whiskers showed that its flexural strength greatly increased with increasing whisker content. Moreover, the composite showed initially an increase in impact strength with a whisker content up to 10 wt%, then showing a slight decrease when the whisker content reached 15 wt%. Scanning electron microscopy observations revealed that the two coupling agents (KH 921 and BE4) employed in this work tend to change the fracture features of the composites from brittleness to that of ductile behaviour. Copyright © 2004 Society of Chemical Industry

The effects of long-term exposure to high temperatures on the ILSS and impact performance of carbon fibre reinforced bismaleimide

Carbon fibre composite materials with high temperature bismaleimide resin systems as the matrix component are currently being used on structures for both military and civilian aircraft. A major concern with these materials is the effect of long-term exposure to service environments on their physical and mechanical properties. A carbon fibre reinforced bismaleimide composite was evaluated to determine the effect of fibre type and exposure to a high temperature environment on its interlaminar-shear strength and impact performance. Interlaminar shear and Charpy notched impact specimens were prepared, aged for certain periods of time at three different temperatures in air-circulating ovens and tested. The results reflected the degradation of matrix and the fibre-matrix interface with ageing, accordingly the interlaminar-shear strength deteriorated progressively and the failure mode of the impact specimens changed from a brittle failure in the unaged state to a progressive delamination in the aged state. Change in the impact failure modes influenced the energy dissipation characteristics of the specimens.

Moisture diffusion and hygrothermal aging in bismaleimide matrix carbon fiber composites—part I: uni-weave composites

Moisture diffusion and hygrothermal aging in uni-weave bismaleimide composites were systematically studied in this research. The moisture weight gain curves of the composites were compared with those of the neat resin in order to determine the interface effect on moisture absorption. Both the neat resin and composites display similar two-stage diffusion behavior, with the first and second stages being diffusion- and relaxation-controlled, respectively. When the diffusivities of the composites were compared to theoretical predications of an appropriate mathematical model, it is found that the fiber-matrix interface has little effect on the short term moisture diffusion. However, the long term absorption is suppressed in the composites. The rigid fiber–matrix interface seems to constrain long-range segmental motions of the matrix and in so doing reduce water absorption in the relaxation-controlled second stage. Although the fiber–matrix bonding is initially very strong, prolonged water absorption at elevated temperatures eventually damage the interface and causes interfacial cracking.

Effect of Isothermal Aging on Ultimate Strength of High-Temperature Composite Materials for SST Structures

The objective of this experimental study was to evaluate the effect of iso-thermal aging on the ultimate strength of three kinds of carbon/high-temperature composite materials, i.e., G40-800/5260 and MR50K/MR2000N bismaleimide composites and T800H/PI-SP amorphous thermoplastic polyimide composite. These materials are current candidate structural materials for a supersonic transport of the next-generation. The hole-notched and unnotched panels, before being machined to specimens, were isothermally aged at 120°C and 180°C for up to 15,000 hours. Static tests at room and elevated temperatures before and after thermal aging provided the open-hole tensile, open-hole compressive, and short beam shear strengths. Moreover, the effects of five oxidation resistant treatments on open-hole compressive strength at 180°C were investigated after isothermal aging of 5,000 hours at 180°C. The test results clarified the effects of isothermal aging on ultimate strengths and oxidation resistant treatments on open-hole compressive strength. Moreover, the possibility of developing an accelerated aging test method is discussed using a modified Larson-Miller type equation.

Recent Advances in Bismaleimides and Epoxy-Lmide/ Bismaleimide Formulations and Composites

In recent years there has been a rapid development in the area of temperature-resistant thermosets. Polyimides in particular are gaining wide acceptance by the industry because they combine a number of unique features, including excellent physical property retention at elevated temperatures and in wet environments, almost constant electrical properties over a wide range of temperatures, and nonflammability properties. Their commercial success is based on the fact that the raw materials, such as aromatic diamines and tetracarboxylic acid dianhydrides, are relatively cheap and the chemical synthesis is, in most instances, straightforward. Polyimides still carry the image of being difficult to process. Considerable effort continues to be devoted to improving the processability without sacrificing thermal stability. The major application for thermosetting polyimides is as matrices in advanced composites.

Processing and characterization of carbon fibre-reinforced polynaphthoxazine composite

In order to attain a high-temperature resistant composite with good performance as well as processability, a polynaphthoxazine composite with 60% by volume of carbon fibre has been successfully developed. The naphthoxazine monomer was modified to obtain lower melting point and higher solubility for improved processability. The density and void content of this composite were measured at room temperature. The Tg and the activation enthalpy of the glass transition process were measured by dynamic mechanical analysis, and the effect of cure temperature on the Tg of the composite was studied. The thermal characteristics of this composite were studied in terms of the weight loss after isothermal ageing, the decomposition temperature from thermogravimetric analysis, and the change in dynamic storage moduli at high temperatures. Flexural and interlaminar shear tests were performed to evaluate the mechanical properties of this composite. A good balance between strength and toughness of this composite was achieved. A very high char yield of 90% was gained after carbonization in a nitrogen atmosphere. This polynaphthoxazine composite compares favourably with the bismaleimide composites in terms of mechanical properties and thermal stabilities.

Development and characterization of high‐performance polybenzoxazine composites

AbstractTo develop high‐performance composites with high temperature resistance, two newly synthesized polybenzoxazines were successfully cured with carbon fiber to obtain composites with 60 vol% fiber. Results from differential scanning calorimetry studies were used to modify the benzoxazine monomers to improve processability in terms of melting point and solubility. The density and void content of these composites were measured. Dynamic mechanical tests were performed to determine the glass transition temperature (Tg) and the activation enthalpy of the glass transition process for these two composites. The effect of cure temperature on the Tg of the composites was investigated. Thermal characteristics were studied by means of dynamic mechanical analysis in terms of isothermal aging, decomposition temperature from thermogravimetric analysis, and storage moduli change at high temperatures. Mechanical evaluations of these composites were conducted by flexural and interlaminar shear tests. The mechanical and thermal properties of these two composites exceed bismaleimide composites and compete with polyimide composites, while exhibiting easier processability than polyimides.

Anisotropic degradation of polymeric composites: From neat resin to composite

AbstractThe degradation of polymer matrix composites was investigated through weight loss measurements. A methodology originally developed based on the shrinking core model was extended to account for matrix orientation, lay‐up sequence, and differences in neat resin and composite degradation. This methodology was derived based on mass transfer and kinetic considerations taking into account the inherent anisotropy and heterogeneity of polymer composites. The model systems used were a bismaleimide (X5260) and a condensation polyimide (Avimid N). Bismaleimide composites were aged at 250, 260, and 270°C in air, whereas both neat resin and composite Avimid N samples were aged at 371°C. Based on the experimentally observed time exponents, the degradation was modeled as diffusion and reaction controlled. The weight losses of both unidirectional and quasi‐isotropic samples were successfully predicted. In addition, correlation between the degradation of neat resin and composite samples was established for the Avimid N system. Finally, this methodology can be used in scaling up weight loss data, providing an important tool in evaluating materials for long‐term use at elevated temperatures.

Surface characterization and adhesive bonding of toughened bismaleimide composites

The use of composite materials in structural applications requires that they be joined or fastened in some manner. The objective of this research was to obtain an improved understanding of the factors which contribute to bond strength and durability in adhesively bonded bismaleimide matrix composites. Composite surface pretreatments included solvent wipe, grit, blast, peel, ply and gas plasma treatment. The results of lap shear and wedge testing in ambient, hot/dry, hot/wet and chemically aggressive environments were correlated to the surface composition after pretreatment as measured by X-ray photoelectron spectroscopy, ion scattering spectroscopy and contact angle analysis. The topography of the pretreated composite surfaces was analysed by scanning electron microscopy and profilometry. Solvent wiping was not effective in removing processing contamination and resulted in poor bond strengths. Peel ply and oxygen plasma pretreatments provided good initial bond strength as well as superior hot/wet durability; however, grit blasting was detrimental to both strength and moisture resistance.

Investigation of the microcracking behavior of bismaleimide composites during thermal aging

AbstractSamples of 16‐ply, quasi‐isotropic bismaleimide composites were aged in convection ovens at 150°C, 177°C, and 204°C for up to 16,000 hours. As a measure of degradation, transverse microcrack density was characterized as a function of time, temperature, and ply depth. Times required to reach onset and saturation crack density were delayed on the tool side of the laminate, for lower temperatures, and for deeper ply depths. Saturation crack densities ranged from 35 cracks/cm to 46 cracks/cm, depending on ply depth. Master curves were constructed for each ply level to express all time‐temperature data for that ply as a single reference curve. A mass transfer analysis further suggests that diffusion is the controlling mechanism in the degradation process. Finally, a prediction of the degradation behavior in the 120,000‐h lifetime of the HSCT aircraft for a sustained temperature of 150°C indicates that ∼13 plies will have reached initiation in a quasi‐isotropic laminate.

The interlaminar fracture behaviour and toughening mechanisms of new carbon fibre-reinforced bismaleimide composites

The interlaminar fracture behaviour of carbon fibre-reinforced bismaleimide (BMI) composites prepared by using a new modified BMI matrix has been investigated by various methods. Laminates of three typical stacking sequences were evaluated. Double cantilever beam, end-notch flexure and edge-delamination tension tests were conducted under conventional conditions and in a scanning electron microscope. The strain energy release rates in Mode I and Mode II, G Ic and G IIc, as well as the total strain energy release rate, G mc, have been determined and found to be higher than those for laminates with an epoxy matrix. Dynamic delamination propagation was also studied. The toughening mechanisms are discussed.

Fatigue fracture behaviour of carbon-fiber-reinforced modified bismaleimide composites

The fracture toughness and fatigue fracture behaviour of carbon-fiber-reinforced modified bismaleimide (BMI) composites have been studied. These composites were found to have higher fracture toughnes, better damage tolerance and longer fatigue life than carbon-fiber composites with epoxy matrices. Delamination is the major mode of failure in fatigue and it is controlled by the properties of the matrix and interface. The improved performance is due to the presence of thermoplastic particles in the modified BMI matrix which gives rise to enhanced fiber/matrix adhesion and more extensive plastic deformation. The fatigue behaviour also depends on the stacking sequence, with the multidirectional [45/90/-45/0] fiber-reinforced modified BMI composite having a lower crack propagation rate and longer fatigue life than the unidirectional laminate. This arises because of the constraint on the damage processes due to the different fiber orientation in the plies.

Generation of thermal strains in carbon fibre-reinforced bismaleimide (PMR-15) composites: Part 2: The effect of volatiles

In this study the moisture absorption behaviour of PMR-15 based carbon fibre composite has been examined. A moisture diffusion isotherm was determined for a sample of the unidirectional laminate, and from this the diffusion coefficient for the material was calculated. An equilibrium moisture absorption isotherm for the material was constructed and analysed. The relationship between equilibrium moisture content, equilibrium methanol content, and residual thermal strain was also investigated, using 0°/90° unbalanced laminate beams.