Bismaleimide Laminate Research Articles

Modulation of dielectric properties of bismaleimide laminates by hyperbranched polyimides with different structures

Modulation of dielectric properties of bismaleimide laminates by hyperbranched polyimides with different structures

Temperature and anisotropy effects in the application of the hindered diffusion model to composite laminates

The one-dimensional hindered diffusion model was applied to gravimetric moisture uptake data for a six-ply high-temperature quartz-fiber-reinforced bismaleimide laminate. Diffusion behavior was evaluated as a function of specimen geometry and temperature to determine the effect on both diffusivity and the binding and unbinding probabilities of diffusing water molecules predicted by the model. Pre-equilibrium experimental uptake data were used to recover model parameters, including equilibrium moisture content, for specimens designed with intentionally-low planar surface-to-edge area ratios of 20, 12.5, and 5. Gravimetric uptake data for fully-immersed laminates at 25°C, 37°C, and 50°C was used to determine diffusion parameters and characterize the temperature and geometry-dependent behavior of the laminate. A parameter recovery method employing least-squares regression was used to determine best-fit parameters of the hindered diffusion model, including diffusivity (DZ), equilibrium moisture content (M∞), ...

Investigation of three-dimensional moisture diffusion modeling and mechanical degradation of carbon/bismaleimide composites under seawater conditioning

The effect of moisture diffusion on the mechanical properties of carbon/bismaleimide composites exposed to seawater conditioning at elevated temperatures was investigated in this study. Carbon/bismaleimide composites with two stacking sequences (unidirectional and cross-ply) were fabricated using out-of-autoclave process. Testing coupons were immersed in the seawater at two elevated temperatures (50℃ and 90℃) for approximately 3 months. Moisture diffusivities and solubility for each type of carbon/bismaleimide specimen were characterized using the experimental data. A three-dimensional dynamic finite element model was developed using these parameters to predict the moisture diffusion behavior in the carbon/bismaleimide laminates. The degradation of mechanical properties due to hygrothermal aging was assessed by short-beam shear and three-point bending tests. It was found that flexural strength and interlaminar shear strength reductions are higher at 90℃ aging than that at 50℃ aging. The reduction in mechanical properties for bismaleimide laminates can be attributed to the fiber/matrix interfacial cracks observed by scanning electron microscopy.

Phase separation morphology and mode II interlaminar fracture toughness of bismaleimide laminates toughened by thermoplastics with triphenylphosphine oxide group

Toughness improvement of bismaleimide (BMI) resin is very important for its application in composite materials. Blending with thermoplastic polymer is usually used to increase the toughness of BMI matrix. In this work we prepared two thermoplastic polymers with polar triphenylphosphine oxide group in the polymer backbone. The synthesized thermoplastics with different polarities were investigated by several physicochemical methods. Then through scanning electronic microscopy we observed the phase separation morphology of BMI blends at different doping concentrations of thermoplastics. Additionally mode II interlaminar fracture toughness G IIC of BMI laminates toughened with thermoplastics by ex-situ method was examined. The results showed that thermoplastic with strong polarity would bind tightly with BMI during curing and the phase-separation structure might be fixed at the primary stage; while secondary phase separation could happen in a relatively weak polarity system. It indicates that by regulating the polarity of thermoplastic, we may control the phase separation morphologies of blending system and the mechanical properties of composite.

Long‐term durability of a water‐contaminated quartz‐reinforced bismaleimide laminate

The long‐term structural viability of a six‐ply water‐contaminated quartz fiber‐reinforced bismaleimide laminate is investigated via dynamic mechanical analysis and flexural strength assessment over a four‐year experimental time frame. Water contamination is achieved via immersion in water at 25°C for short‐term (2 weeks and 1 month), long‐term (6 months), and very long‐term (4 years) duration. Long‐term moisture uptake exhibits distinctly non‐Fickian behavior. Maximum moisture content exceeds 1.5% by weight after four years of immersion. Laminates exhibit a remarkable resistance to degradation for all exposure durations. Flexural strength decreased by roughly 5% in the worst case. Further, no significant change in glass transition temperature was observed. Scanning electron microscopy revealed no micro‐crack formation and a relatively low incidence of fiber–matrix debond. Experimental evidence suggests that quartz fiber‐reinforced bismaleimide is a viable option for long‐term moisture‐prone structural applications at moderate temperatures. POLYM. COMPOS., 39:2643–2649, 2018. © 2016 Society of Plastics Engineers

Projecting long-term non-Fickian diffusion behavior in polymeric composites based on short-term data: a 5-year validation study

The slow approach to equilibrium concentration indicative of non-Fickian diffusion in polymer composites necessitates experimental time frames which are often of limited feasibility. As a result, experimental studies are terminated prematurely due to time constraints or incorrect identification of equilibrium. Here, the three-dimensional anisotropic diffusion behaviors of six-, twelve-, and forty-ply quartz-reinforced bismaleimide laminates are quantified through a 5-year, full-immersion gravimetric absorption study. The applicability of the three-dimensional hindered diffusion model is investigated, while projections of future absorption behavior made at 21 months are revisited in light of 3 years of additional data. The mathematical equivalency of the hindered diffusion model and a diffusion–relaxation model under certain conditions is discussed. Moisture content rises continuously throughout the 5-year experiment for all samples. In the six-ply case, the standard termination criterion for the equilibrium condition is met before 6 months and 1.38 % moisture content by weight. Actual moisture content reaches 1.56 % after 5 years. The hindered diffusion model and associated forward projections of moisture content are found to conform well to experimental results.

The effect of moisture contamination on the relative permittivity of polymeric composite radar-protecting structures at X-band

The impact of absorbed moisture on the X-band relative permittivity of three composite materials used in aircraft radar-protecting structures (radomes) is investigated, quantified, and analyzed with respect to existing effective medium theories. Two glass-fiber-reinforced epoxy laminates and a quartz-fiber reinforced bismaleimide laminate are fabricated, contaminated with water, and analyzed with a split-post dielectric resonator in order to determine moisture-induced relative permittivity changes at 10GHz. In the most significant case, a 3.7% increase in water content by weight resulted in a 43% increase in relative permittivity for BMI/quartz laminates. Such an increase may be a root cause of radome-induced radar performance loss for long-service-life aircraft. The relationship between absorbed water volume and relative permittivity is not well described by the existing effective medium theories considered. Support is given to the existence of conditions which lead to restricted molecular dipole rotation of water within a polymer network and a resulting “effective” relative permittivity of water based on polymer chemistry and morphology. A simple power-law expression predicated upon this assumption successfully describes the relative permittivity increase as a result of absorbed water prior to equilibrium moisture condition.

A novel numerical–experimental approach for predicting delamination in high temperature polymer matrix composites

In this paper, a novel numerical–experimental methodology is outlined to determine cohesive stress and damage evolution parameters for pristine as well as isothermally aged (in air) polymer matrix composites. A rate-dependent viscoelastic cohesive layer model was implemented in an in-house test-bed finite element analysis (FEA) code to simulate the delamination initiation and propagation in unidirectional polymer composites before and after aging. To determine the model parameters, double cantilever beam (DCB) experiments were conducted on both pristine and isothermally aged IM-7/bismaleimide (BMI) composite specimens. The J-integral approach was adapted to extract cohesive stresses near the crack tip. A principal-stretch dependent internal damage state variable defines the damage in the cohesive layer. Within the cohesive layer, pristine and cohesive stresses were compared to estimate the damage parameters.Once the damage parameters had been characterized, the test-bed FEA code employed a micromechanics based viscoelastic cohesive layer model to simulate interlaminar delamination. The present cohesive-layer based FEA model was able to accurately predict not only the macro-level load–displacement curve, but also the micro-level crack growth history in IM-7/BMI laminate before and after thermal aging.

Three-dimensional anisotropic moisture absorption in quartz-reinforced bismaleimide laminates

The three-dimensional anisotropic moisture absorption behavior of quartz-fiber-reinforced bismaleimide (BMI) laminates is investigated by collecting 21 months of experimental gravimetric data. Laminates of six, twelve, and forty plies and various planar aspect ratios are used to determine the three-dimensional anisotropic diffusion behavior when exposed to full immersion in distilled water at 25°C. The long-term moisture absorption behavior deviates from the widely used Fickian model, but can be accurately captured by the three-dimensional, anisotropic hindered diffusion model (3D HDM). Excellent agreement is achieved between experimental gravimetric data and the 3D HDM for all laminate thicknesses. Recovered model parameters are shown to slightly vary with laminate thickness due to the small changes in the cured-ply thickness. However, model parameters identified for a given laminate thickness are observed to accurately predict the absorption behavior of samples with different planar dimensions. Equilibrium moisture content of 1.72, 1.69, and 1.84% and corresponding diffusion hindrance coefficients of 0.807, 0.844, and 0.671 are recovered for six, twelve, and forty-ply laminates, respectively, thus confirming strong non-Fickian behavior. Moisture absorption parameters may be determined successfully at 16.5 months of immersion, before reaching approximately 85% of the equilibrium moisture content at 21 months. Subsequent gravimetric measurements up to 21 months are consistent with the predicted long-term behavior. POLYM. ENG. SCI., 54:137–146, 2014. © 2013 Society of Plastics Engineers

Improvement of the Impact Damage Resistance of BMI/Graphite Laminates by the Ex-situ Method

High-performance bismaleimide (BMI) matrix composites reinforced with graphite fibers were prepared and toughened with a thermoplastic component (PEK-C) by using different toughening methods. Four experimental options were conducted using the neat BMI matrix, toughened BMI matrix with PEKC, BMI laminates periodically interleaved with neat PEK-C films (Ex-situ concept 1) and BMI laminates periodically interleaved with BMI/PEK-C blend films (Ex-situ concept 2), respectively. The laminates were tested for compression strength after impact using an impact energy of 2 J mm-1. The highest impact damage resistance was obtained for the laminates toughened using the Ex-situ concept 2, especially, when PEK-C/BMI two-component films, cast from a mixture of PEK-C: BMI = 60: 40 were interleaved between the BMI laminate plies. Interleaving the pure thermoplastic film also gave good results (Ex-situ concept 1). There were two peak temperatures evident in the dynamic mechanical thermal analyses of the ex-situ toughened laminates implying that phase separation had occurred. The glass transition temperature of the toughened BMI laminates was slightly reduced due to the lower glass transition temperature of PEK-C. Morphological investigations revealed that a granular structure was present in the interply region presumably due to spinodal decomposition and coarsening. The results of this study are presented herein.

The effect of isothermal aging on transverse crack development in carbon fiber reinforced cross‐ply laminates

AbstractAn investigation into the effect of isothermal aging on the development of transverse cracks in cross‐ply laminates of two high temperature composite systems was performed. The composite materials investigated were BASF X5260/640–800 and DuPont Avimid K/IM6. Changes in the glass transition temperature, composite weight loss, crack density, and mode I intralaminar fracture toughness were monitored during isothermal aging in air at 177°C for up to 2232 h. The two laminate configurations used in this study include two variations of the generic cross‐ply configuration [02/90n]s, in which n equals 1 and 2. The results of this investigation show that a layer of degraded material forms at the surface of the X5260/640–800 bismaleimide laminates and that the thickness of the degraded layer increases with aging time. After 744 h of aging, transverse cracks form in the surface plies and an increasing crack density evolves as aging time is increased; however, transverse cracks do not form in the inner 90° ply groups with aging during the time period investigated. The Avimid K/IM6 thermoplastic polyimide laminates, which show evidence of cracking prior to aging, do not exhibit any significant change in crack density with aging. The results of the aging experiments also show that the bismaleimide system exhibits a weight loss of 1.5% and an increase in glass transition temperature from 250°C to 300°C after 2232 h of aging at 177°C, while the thermoplastic polyimide system shows a weight loss of only 0.05% and an increase in glass transition temperature from 280 to 285°C after 2232 h. Changes in the resistance to crack formation are also seen in these materials during aging. The mode I intralaminar fracture toughness, a measure of resistance to transverse crack formation, shows a 50% decrease after aging for 2232 h for the bismaleimide system, while the behavior exhibited by the thermoplastic polyimide shows little evidence of a reduction.