With the extensive use of composite materials in aviation industry, the research of holes which affect composite residual strength has become very important. Based on MSC.Nastran, the stress of each laminate unit was calculated. Failure factor of composite laminates containing holes were calculated with the Tsai-Wu failure criterion. In this paper, the influence of hole shape and size on the composite laminate failure factor under compressive loading was studied. The relationship of hole shape, size and residual strength of composite laminates was briefly discussed. The results show that, under compressive loading, the stress concentration appears near the hole, there is a proportional relationship between the failure factor and hole size, the hole size and residual strength is the inverse relation.

Microwave absorbing properties of composites containing activated carbon-fiber felt screens (ACFFSs) have been investigated. Samples with different types of ACFFSs embedded in composites were fabricated. Experiments were carried out to test the absorption effect of embedded ACFFSs. It is found that both the ACFFS patterns and its element configurations are critical for the reflection properties of samples. With the distance between strips and the width of strips in the inductive ACFFS decreased, the absorbing properties of composites are improved. The composite obtains a reflection loss below –10dB in 8~18GHz, which is the frequency range the radar works in, when the distance between strips and the width of strips are 7mm and 5mm respectively. With the side of plates and the distance between plates in the capacitive ACFFS reduced, the absorption effect of composites rises. When the distance between plates and the side of plates are 5mm and 7mm separately, the composite achieves a reflection loss below –10dB over a bandwidth of 8.7GHz and the minimum value of absorption rate reaches –31.7dB.

Microwave absorbing materials (MAMs) is a key component for weapon systems such as aircrafts, warships, and missiles to achieve the stealth performance by absorbing electromagnetic waves incident on. In this work, activated carbon fibers (ACFs) with average length of 1-3mm were prepared, and ACFs dielectric properties were investigated. The results show that ACFs have the frequency response effect, which is helpful for broadening the absorbing bands. According to ACF permittivity, the optimal design is carried out for four-layer microwave absorbing composites with thickness of 4mm based on the impedance matching design method. Following the optimization results the four-layer absorbing material was prepared, and it obtains a reflection loss below -10dB over 8GHz and the minimum value reaches -39.3dB in 2-18GHz.

The result shows: If probabilistic methods were used to conduct compliance analysis for composite structure damage tolerance. When the impact energy is low, calculated result should conservatively use probabilistic methods of Weibull distribution fitting; when the impact energy is high, calculated result should conservatively use probabilistic methods of logarithmic linear fitting.

In this paper, the probabilistic compliance methodology for damage tolerance design of thicker composite structures were investigated, and the research results show that for the composite laminates withstanding impact energy below 90J, if it cannot produce barely visible impact damage (BVID), then using the probabilistic methodology can meet certification requirements of damage tolerance.