Engineering topics

Atkins, A. G.

Publications and source records attributed to Atkins, A. G..

7 records

NASA NTRS1976

Effect of water and ice on strength and fracture toughness of intermittently bonded boron-epoxy composites

The effects of water and ice on the strength and fracture toughness of boron-epoxy composites with polyurethane intermittent bonding have been investigated. Neither simple soaking in water nor soaking followed by freezing and thawing have marked effects on the strength of the fully-coated composites, but they have disastrous effects on the uncoated composites. Toughness is affected only marginally, with some small reductions in the fully-coated samples, and with essentially no effect on the uncoated composites. An analysis is presented which explains adequately the experimental strength and toughness results obtained, and which is based on an argument that water absorption reduces the interfacial shear strength only of the uncoated areas and not those regions coated by the polyurethane varnish. The results indicate that the advantages of appropriate intermittent bonding (i.e., high strength combined with high toughness) are retained in wet conditions so that such composites may be favorably used in such adverse environmental conditions.

Atkins, A. G.↗

NASA NTRS1975

Fiber reinforced solids possessing great fracture toughness: The role of interfacial strength

The results of angle-ply investigations for strength and toughness of brittle fiber/brittle filament composites are presented. General results are discussed for both unidirectional and angle-ply intermittently bonded boron/epoxy composites as affected by soaking and freezing water environments. A description of and the operating instructions are included for the modified 230 mm (9 inch) wide intermittent coating tape making apparatus.

Atkins, A. G.↗

NASA NTRS1975

Intermittent bonding for high toughness/high strength composites

An analysis of toughness and strength in intermittently bonded brittle filament/brittle matrix composites is presented that shows the importance of the coating material in achieving high toughness properties. Some observations are made on methods of measuring the components of toughness in composites. Both a mathematical model and experimental results are incorporated into the discussion.

Atkins, A. G.↗

NASA NTRS1975

Large fracture toughness boron-epoxy composites

The high tensile strengths of strong interfacial bonding may be combined with the large fracture toughness of weak interfacial bonding in brittle fiber/brittle matrix composites by intermittently coating the filaments before layup so as to have random alternate weak and strong regions. Appropriate coating materials enable Cook-Gordon Mode I interfacial debonding to take place, which produces very long pull-out lengths with an associated large contribution to toughness. Unidirectional boron-epoxy composites have been so made which have toughnesses greater than 200 kJ/sq m while retaining rule of mixtures tensile strengths. Similar trends have been observed for crossply layups.

Atkins, A. G.↗

NASA NTRS1975

Controlled intermittent interfacial bond concept for composite materials

Concept will enhance fracture resistance of high-strength filamentary composite without degrading its tensile strength or elastic modulus. Concept provides more economical composite systems, tailored for specific applications, and composite materials with mechanical properties, such as tensile strength, fracture strain, and fracture toughness, that can be optimized.

Marston, T. U.↗

NASA NTRS1974

Imparting strength and toughness to brittle composites

Appropriate intermittent coatings of fibers can produce areas of low and high toughness in brittle composites. Experiments using silicon vacuum grease (SVG) and polyurethane varnish (PUV) coatings that achieve weakly and strongly bonded interfaces are described. Tensile strength and edge-crack fracture toughness for both SVG and PUV coatings were plotted against the percentage coating (C). Both coating materials maintain tensile strengths in the order of the rule of mixture strength values up to a large C. It is suggested that both materials produce similar coated interfacial shear strengths while producing different effects on toughness.

Atkins, A. G.↗

NASA NTRS1974

Fiber reinforced solids possessing great fracture toughness: The role of interfacial strength

The high tensile strength characteristic of strong interfacial filament/matrix bonding can be combined with the high fracture toughness of weak interfacial bonding, when the filaments are arranged to have alternate sections of high and low shear stress (and low and high toughness). Such weak and strong areas can be achieved by appropriate intermittent coating of the fibers. An analysis is presented for toughness and strength which demonstrates, in broad terms, the effects of varying the coating parameters of concern. Results show that the toughness of interfaces is an important parameter, differences in which may not be shown up in terms of interfacial strength. Some observations are made upon methods of measuring the components of toughness in composites.

Atkins, A. G.↗