Noboru Komatsu

Mechanism of high energy absorption by foamed materials-foamed rigid polyurethane and foamed glass

Energy absorbability of foamed rigid materials, polyurethane and glass, was studied under a compressive load. The brittle materials were proved to absorb much energy in a manner similar to ductile materials. A mechanism for such high energy absorption was proposed, based on a fracture model in which crushing of cells initiates at the weakest cell followed by propagation to cells lying in the layer containing the weakest one and lying in a direction perpendicular to the compressive force; then the crushing propagates to another layer under the compressive force after the completion of the first layer crushing. In the period of one layer crushing, the strain energy stored in the period of compression prior to the crushing is temporarily released, and it is stored again in the period of compression after the crushing. The store and release of strain energy is assumed to be repeated until all cell layers are crushed. This mechanism of layer-by-layer crushing allows the cells to absorb strain energy repeatedly, and causes high energy absorption in the brittle foamed material. The calculated energy based on the mechanism agrees well with the observed one.

Effects of Cu on impact strength of Al-Si alloys

Effects of Cu on the impact strength and structures of Al-Si alloys were examined by means of Charpy impact test and metallographical method. The following three types of specimens were used:a) As cast.b) Solution heat treated at 500°C for 240min. for the above specimens.c) Artificially age hardened at 200°C for 300min. after the above solution heat treatment.(1) The impact strength of as cast alloys tended to be decreased with the increase in Si content and Cu addition. When Si content was low (approximately below 4%), the strength was markedly decreased with the addition of Cu. However, the strength was gradually decreased with increasing Si content and no effects of Cu were seen on the strength at about 15% of Si content.(2) By the addition of a small amount of Cu to the hypo-eutectic alloy of nearly eutectic composition with no primary Si crystals, a marked decrease of the impact strength was seen on the specimens solution heat treated at 500°C. The above decrease resulted from the formation of primary Si crystals due to the addition of Cu. The configuration of these primary Si crystals was the cause of stress concentration as reported in the previous paper, 1) and it was kept unchanged by holding at 500°C.(3) The impact strength of the alloys, which had been artificially age hardened at 200°C after solution heat treatment at 500°C, tended to be decreased with the increase in Si content and Cu additioon. Especially, the effect of Cu addition was greater than that of Si content.

Effects of Be on impact strength of Al-Si alloys containing Fe

Effects of solution treatment and addition of a small amount of Be on the impact strength and structure of Al-Si alloys containing Fe were examined by means of impact tests.The results obtained were summarized as follows.(1) The impact strength of Al-11% Si alloys was linearly decreased with increasing Fe content in the range beyond 0.13% Fe. After solution treatment at 500°C, the strength was markedly improved when Fe content was smaller, and the effect diappeared at about 1.5% of the content.(2) The impact strength of Al-11% Si alloys tended to be decreased with the addition of Be, both for as cast and heat treated (at 500%C) alloys.After Al-13% Si alloys containing Fe, to which Be had been added, was heat treated, the strength was markedly varied according to Fe content. It was kept nearly constant up to 1.02 or 1.32% of Fe by the addition of 0.2 or 0.5% Be, respectively.(3) Acicular crystallites were observed in Al-Si alloys, which had lower impact strength with decreasing Fe content. However, the shape of crystallites was converted into roundish patterns of Chinese script character type.