Stitching Repair for Delaminated Carbon Fiber/Bismaleimide Composite Laminates.

Due to the excellent mechanical properties and heat resistance, bismaleimide matrix composite materials have been widely used in aircraft. However, they are susceptible to low-energy impacts, such as bird hits, gravel, tools falling, etc., which can easily result in delamination. The delamination can significantly reduce the compression performance of composites and become a potential hazard for aircraft in service. In this paper, a stitching method developed from the Z-pin manufacturing process was proposed to repair delaminated laminates. Firstly, the delaminated area was stitched by fiber bundles that were pre-impregnated with glue. Then, the fiber bundles threading through the laminate become the pins after the curing process, thus producing the bridging effect between delaminated layers. As a result, the in-plane compressive properties of the laminate are enhanced. The parameters, including the size, number, and position of the stitching hole, for the stitching repair were optimized, and the factors affecting the repair effect were discussed through both finite element analysis and experiments. The results showed that for a carbon fiber/bismaleimide composite plate with a circular delamination roughly 30 mm in diameter, the in-plane compressive strength can be recovered from 54.45% to 84.23% of the pristine plate, and the modulus was fully recovered.

Preparation of phase change material filled hybrid 2D/3D graphene structure with ultra-high thermal effusivity for effective thermal management.

Graphene-based energy storage and renewable material has increasingly attracted research interest, due to its high thermal conductivity and light weight. Researchers fill phase change material (PCM) into three-dimensional graphene foam, to obtain a composite with high energy storage capability and moderate thermal conductivity. However, this kind of composite's heat transfer mode is single and cannot maximize the advantages of graphene. Herein, a stearic acid filled graphene-foam composite (GFSAC) connected with graphene paper (GP) through gravity-assisted wetting attaching process is demonstrated in this paper.•GP is obtained by thermal reduction of graphene oxide (GO) paper. Its in-plane thermal conductivity can reach up to 938 Wm-1 K-1. By controlling the preparation process of GO paper, the in-plane thermal conductivity of GP can be adjusted.•GFSAC is consisted of GF and SA, GFSAC with different heat transfer properties can be prepared by adjusting the degree of reduction of GF.•A novel gravity-assisted wetting attaching process has been developed to prepare GP/GFSAC/GP composite, which can effectively reduce the thermal resistance between GP and GFSAC. The effective thermal effusivity of the final GP/GFSAC/GP composite reaches 18.45 J cm-3/2 m-1/2 s-1/2 K-1/2, showing an excellent thermal management capability.

Radioactivity measurement of 85Kr by using anti-cosmic HPGe γ spectrometer.

In order to improve the detection sensitivity of 85Kr, an anti-cosmic HPGe γ spectrometer was established and a specific Marinelli beaker was designed for 85Kr measurement. Comparing to the non-anticoincidence γ spectrum, the integral background counts rate range from 20 to 2400 keV was reduced by a factor of 5.17 using anticoincidence shielding. The minimum detectable activity of 85Kr was 10.5 Bq within 24 h measurement in standard mode and that of 3.99 Bq in anticoincidence mode. The activity concentration of atmospheric 85Kr was preliminarily measured to be an average of 1.30 Bq/m3 in Beijing and corresponding minimum detectable concentration was 0.2 Bq/m3.