Search

The carbon fiber/epoxy resin composites with different stitch density were manufactured using modified lock stitching and vacuum assisted resin infusion (VARI) molding process. The influence of stitch space and stitch pitch on mechanical properties of the composites was investigated. The optimum stitch density was obtained. The results show that with increasing stitch space, both tensile and flexural properties enhance and interlaminar shear strength increases first and then decreases. With the increase of stitch pitch, both tensile and flexural properties exhibit an increasing trend. The stitched composites have the optimum integrated mechanical properties when the stitch density is 5 mm×8 mm. Their tensile strength, tensile modulus, flexural strength and flexural modulus reduce by 13.3%, 12.7%, 23.0% and 25.2%, respectively, whereas the interlaminar shear strength increases by 11.3% compared to the unstitched composites.

Polycrystalline Ni50Mn35In15 alloy was fabricated by arc-melting, and its martensitic transformation and magnetocaloric effect were systematically investigated with magnetic property measurement. The experimental results indicated that, with decrease of temperature, the second-order magnetic transition and the martensitic transition with characteristic of the first-order structural transition happened successively near room temperature, leading to an abrupt change of magnetization. At the same time, exchange bias was found by means of hysteresis loop measurement at low temperature, which clearly suggested coexistence of ferromagnetic and anti-ferromagnetic phases at low temperatures. In addition, a large magnetic entropy change during martensitic transition was calculated from Maxwell equations. Its value can reach 22.3 J/kg K at 309K in applied field of 5T.

The martensitic transition and magnetocaloric property in Ni50Mn25+xSn25-x (x=11, 12) Heusler alloys were investigated by means of structure and magnetism measurements. The results show that the antiferromagnetic interaction strengthens in the martensitic state, leading to the coexistence of ferromagnetic and antiferromagnetic interaction in this state, which is different from the magnetic property of austenitic state in these alloys. Furthermore, based on Maxwell equation, the inverse magnetocaloric property near martensitic transition temperature of this system was studied. It was found that large positive magnetic entropy change (ΔSM) depends on both magnetic jumping (ΔM) and temperature region during martensitic transition.