In this study, an assessment of the composite processing-related properties of a newly developed 6-FDA-based phenylethynyl-terminated polyimide (available under the tradename NEXIMID®MHT-R) is presented. Processing schemes, used for preparing high quality carbon fibre-reinforced composites by the use of conventional resin transfer moulding are developed and presented. The influences of manufacturing parameters on glass transition temperature of the composites are presented. The results confirm that composites with exceptionally high Tg, in the range between 350 and 460℃ can be achieved. A manufacturing scheme that yields in composites with Tg of 370℃ is presented and proposed as a good candidate to serve as baseline for further studies.

In this study, the mechanical performance assessment of a newly developed carbon fibre-reinforced polyimide composite system T650/NEXIMID (R) MHT-R is presented. This system was subjected to a series of mechanical tests at ambient and elevated temperature (320?) to determine basic material properties. Moreover, an additional test was conducted, using a T650/NEXIMID (R) MHT-R laminate in which the fibre sizing was thermally removed prior to laminate manufacturing, to investigate the effect of fibre treatment on mechanical performance. The experimental results indicated that the T650/NEXIMID (R) MHT-R composites along with exceptionally high T-g (360-420?) exhibited competitive mechanical properties to other commercially available polyimide and epoxy-based systems. At elevated temperature, the fibre-dominated properties were not affected whilst the properties defined by matrix and fibre/matrix interface were degraded by approximately 20-30%. Finally, the fibre sizing removal did not affect the tensile and compressive strength, however, the shear strength obtained from short-beam shear test was deteriorated by approximately 15%.

Helmets are the most important piece of protective equipment for motorcyclists. The liner of the helmet is the main part of the helmet which dissipates the impact energy and mitigates the load transmitted to the head. Therefore, optimizing the material that absorbs most of the impact energy would improve the helmet's protection capacity. It is known that the energy absorption of the helmet liner can be optimized by means of using liners with varying properties through the thickness, however currently the majority of used liners exhibit constant properties through the thickness. Advances in the field of topology optimization and additive manufacturing provide the ability of building complex geometries and tailoring mechanical properties. Along those lines, in the present work the feasibility of using a hierarchical lattice liner for helmets was studied. Finite element method was employed to study whether a hierarchical lattice liner could reduce the risk of head injuries in comparison to currently used liner materials. The results show that using a hierarchical lattice liner has the potential of significantly reducing the risk of head injury compared to a helmet with traditional EPS liner and could potentially be considered as the new generation of energy absorbing liners for helmets.

Isolating and observing the damage mechanisms associated with low-velocity impact in composites using traditional experiments can be challenging, due to damage process complexity and high strain rates. In this work, a new test method is presented that provides a means to study, in detail, the interaction of common impact damage mechanisms, namely delamination, matrix cracking, and delamination-migration, in a context less challenging than a real impact event. Carbon fiber reinforced polymer specimens containing a thin insert in one region were loaded in a biaxial-bending state of deformation. As a result, three-dimensional damage processes, involving delaminations at no more than three different interfaces that interact with one another via transverse matrix cracks, were observed and documented using ultrasonic testing and X-ray computed tomography. The data generated by the test is intended for use in numerical model validation. Simulations of this test are included in Part II of this paper.

In this paper, the hybridisation of multidirectional carbon fibre-reinforced composites as a means of improving the compressive performance is studied. The aim is to thoroughly investigate how hybridisation influences the laminate behaviour under different compression conditions and thus provide an explanation of the "hybrid effect". The chosen approach was to compare the compressive performance of two monolithic carbon fibre/epoxy systems, CYTEC HTS/MTM44-1 and IMS/MTM44-1, with that of their respective hybrids. This was done by keeping the same layup throughout ((0/90/45/-45)2S) while replacing the angle plies in one case or the orthogonal plies in the other case with the second material, thus producing two hybrid systems. To investigate the compressive performance of these configurations, compact and plain compression test methods were employed which also allowed studying the sensitivity of compressive failure to specimen geometry and loading conditions. The experimental results and the subsequent fractographic analysis revealed that the hybridisation of selective ply interfaces influenced the location and severity of the failure mechanisms. Finally, in light of this knowledge, an update of the generic sequence of events, previously suggested by the authors, which lead to global fracture in multidirectional fibre-reinforced composites under compression is presented. 

Fractographic analysis, i.e. the examination and interpretation of fracture surfaces, provides an insight into the causes and location of failure. Previously considered as a "black art", specialists now relate fracture morphologies to failure mechanisms with confidence and provide information about the failure sequence and source of failure initiation. This technique gives great feedback and can allow better design for next-generation parts.

In this paper, we report the development of a glass fiber commingled composite (GFCC) based on a nanoclay-doped polyamide 6 (PA6) and the evaluation of its fire reaction. The preparation of the composite comprised several steps. Firstly, the nanoclay was dispersed in the PA6 matrix. Then, the produced compound was spun in filaments and commingled with continuous glass fibers. Finally, the laminate preform was consolidated. Reference samples based on the neat PA6 were produced as well. As a results, although it is well known that, in the presence of a relevant amount of continuous fibers, the behavior of the material is mainly driven by the fibers themselves (e.g. mechanical, thermal, conductive, and so on), the effect of the clay was interesting, especially in flammability test (UL94 vertical burning test), where the total burning time passes from 227 s to 146 s.

The current communication present results from work on polymeric composites with extreme temperature performance. This study focuses on carbon fibre composites based on a new phenyl ethynyl terminated polyimide formulation NEXIMID® MHT-R (Nexam Chemicals AB, Sweden) based on hexafluoroisopropylidene bisphthalic dianhydride (6-FDA), 4-(Phenylethynyl)Phthalic Anhydride (4-PEPA) and ethynyl bis-phthalic anhydride (EBPA). In particular influence of post-cure conditions such as time, temperature and atmosphere on Tg of the composites is investigated. In addition to this monitoring and analyses of the consequences of post-cure on mass loss and occurrence of micro-cracks is carried out. Three different post-curing temperatures are considered in this study: 400°C, 420°C and 440°C. Two different atmospheres, air and inert by nitrogen, were also investigated. In summary the results reveal that remarkably high Tg, up to around 460°C, is achieved with only very limited mass loss. It was also observed that some, but limited amounts of, micro-cracks are developed within the laminates due to the inevitable high thermal stresses generated upon cooling from cure temperature.

In this study, an assessment of the mechanical performance of a newly developed carbon fibre-reinforced polyimide composite system T650/NEXIMID® MHT-R is presented. This system was subjected to a series of mechanical tests at ambient temperature in order to determine the tensile, compressive, flexural and interlaminar shear properties. Moreover, an additional testing campaign was conducted, using a T650/NEXIMID® MHT-R laminate in which the sizing had been thermally removed prior to manufacturing, in order to investigate the effect of fiber treatment on the mechanical performance. The experimental results indicated that the T650/NEXIMID® MHT-R composites along with exceptionally high Tg (~370-420ºC) exhibited very good elastic properties in comparison with other polyimide and epoxy-based systems and, although slightly lower than the best results from literature, promising strength values. Finally, the thermal removal of the sizing did not affect the tensile, compression and flexural properties, however the interlaminar shear strength was significantly deteriorated.

In this paper, we report the development of a glass fiber commingled composite (GFCC) based on a nanoclay-doped polyamide 6 (PA6) and the evaluation of its combustion behavior. The preparation of the composite has involved several steps. Firstly the nanoclay was dispersed in the PA6 matrix. Then, the produced compound was spun in filaments and commingled with glass fibers. Finally, the laminate preform was consolidated. In order to evaluate the effect of the nanoclay on the combustion behavior of the GFCC, samples based on the neat PA6 were produced as well. The results show that the effect of the nanocomposite matrix was a significant improvement regarding heat release when a continuous external heat flux is applied (cone calorimeter), whereas in the presence of the glass fibers the positive effect is more pronounced in tests where a small flame is induced to ignite the vertically oriented sample (UL94 vertical burning test). This is connected to the different mechanisms by which the nanoclay affects the combustion behavior, whether in the presence of glass fibers or not.