Aramid

Dynamic properties of materials such as aramid and polyethylene fiber reinforced composites are rarely found in the literature, in spite of their significance in ballistic design. It is also difficult to find detailed descriptions of the testing techniques and procedures to characterize these materials. This paper describes a dynamic tensile testing technique for these composite materials, and discusses problems such as the specimen size and the clamping system. A full numerical simulation is performed in Autodyn-2D to elucidate what is happening during the experiment. Finally this testing technique is applied to show that reliable data can be obtained from the Hopkinson bar for aramid and polyethylene fiber reinforced composites. Stress-strain, stress versus rate of strain and strain versus rate of strain curves are included. The results indicate that for these materials the tensile strength rises with the strain rate while the maximum strain diminishes in the range studied.

A Lunar Space Elevator [LSE] can be built today from existing commercial polymers; manufactured, launched and deployed for less than $2B. A prototype weighing 48 tons with 100 kg payload can be launched by 3 Falcon-Heavy's, and will pay for itself in 53 sample return cycles within one month. It reduces the cost of soft landing on the Moon at least threefold, and sample return cost at least ninefold. Many benefits would arise. A near side LSE can enable valuable science mission, as well as mine valuable resources and ship to market in cislunar space, LEO and Earth's surface. A far-side LSE can facilitate construction and operation of a super sensitive radio astronomy facility shielded from terrestrial interference by the Moon. The LSE would facilitate substantial acceleration of human expansion beyond LEO.

The cut and puncture resistance of thermoplastic (TP) impregnated, woven aramid fabric is characterized under quasi-static and dynamic stab testing conditions. Polyethylene, Surlyn®, and co-extruded polyethylene–Surlyn films of various thicknesses are laminated into fabrics and compared with neat fabrics at equal weights and layer counts. The results show that TP-laminated fabrics improve the stab and puncture resistance of the fabrics, through a combination of increased cut resistance and reduced windowing. All films are shown to be effective, although thin Surlyn films appear to provide the best overall performance. The results also show that the TP films need to be integrally bonded to the fabrics in order to achieve synergistic property enhancement.

Synthetic fiber ropes are characterized by a very complex architecture and a hierarchical structure. Considering the fiber rope architecture, to pass from fiber to rope structure behavior, two scale transition models are necessary, used in sequence: one is devoted to an assembly of a large number of twisted components (multilayered), whereas the second is suitable for a structure with a central straight core and six helical wires (1 + 6). The part I of this paper first describes the development of a model for the static behavior of a fibrous structure with a large number of twisted components. Tests were then performed on two different structures subjected to axial loads. Using the model presented here the axial stiffness of the structures has been predicted and good agreement with measured values is obtained. A companion paper (Ghoreishi, S.R. et al., in press. Analytical modeling of synthetic fiber ropes, part II: A linear elastic model for 1 + 6 fibrous structures, International Journal of Solids and Structures, doi:10.1016/j.ijsolstr.2006.08.032) presents the second model to predict the mechanical behavior of a 1 + 6 fibrous structure.

To modify the surface properties of aramid fibre, graft polymerization of acrylamide (AAm) and glycidyl methacrylate (GMA) was performed onto the surface of Kevlar 49. Following plasma treatment and subsequent exposure to air to introduce peroxides onto the fibre surface, the polymer peroxides were decomposed in the monomer solution containing riboflavin by ultraviolet (u.v.) irradiation to effect graft polymerization of the monomers onto the fibre. The monomer solution was prepared from water and dioxane for AAm and GMA, respectively. After removal of homopolymers, the grafted fibre was subjected to surface analysis with attenuated total reflection Fourier-transform infra-red spectroscopy and X-ray photoelectron spectroscopy (XPS). It was found that grafted PAAm and PGMA chains were present in the surface region of the fibre. Graft polymerization was greatly affected by u.v. irradiation time, monomer concentration and plasma treatment time. The reaction of propylamine with the PGMA-grafted surface was accompanied by the appearance of a new nitrogen peak in the XPS spectrum, suggesting the presence of epoxy groups on the surface of PGMA-grafted fibre.

A series of segmented multiblock copolymers containing aramid hard segments and extended polycaprolactone soft segments (with an M n of 4,200 or 8,200 g mol-1) was prepared and tested for their shape-memory properties. Chain extenders were essential to raise the hard segment concentration so that an extended rubbery plateau could be observed. Dynamic mechanical thermal analysis provided a useful guide in identifying (i) the presence of a rubbery plateau, (ii) the flow temperature, and (iii) the temperature when samples started to deform irreversibly.