Search

Carbon fiber-reinforced epoxy composites are widely used in the primary structure of aircraft, the compressive strength of which after impact is an important part in the evaluation of damage tolerance. At present, it mainly relies on a large number of tests to obtain compressive strength after impact in the engineering project. Therefore, it is necessary to develop a simple mathematical model to describe the compressive strength law after impact. A novel mathematical model for fitting compressive strength data of composite laminate after impact was proposed. Using the mathematical model and the initial model parameters, the compressive strength data after impact at different impact energy could be converted into some equivalent undamaged compressive strength data. Then, these equivalent undamaged compressive strength data were normally fitted using the maximum-likelihood estimate (MLE) method to obtain the standard deviation of normal distribution. The above steps was repeated until the minimum estimator of standard deviation was obtained. Hence, the best estimators of parameters for the mathematical model were determined. In order to further demonstrate the applicability of the mathematical model, post-impact compressive strength tests including different thicknesses, layup proportion, and material types were conducted, and the experimental data were fitted with the model. The results indicate that the mathematical model has a good applicability to the compressive strength test data after impact including different thicknesses, layup proportions, and material types.

Ecotourism is the main trend of global tourism development, and evaluating the ecotourism environmental carrying capacity (EECC) of ecologically fragile areas can provide a scientific basis for the sustainable development of regional tourism. This study uses the typical fragile mountain area, the Qilian Mountains (QLMs), as an example and analyzes the spatial and temporal changes in EECC by constructing an evaluation indicator system of EECC, which is based on the framework of "natural ecological environment support—socio-economic pressure—tourism activity pressure". In the results, it is found that the natural ecological environment support, socio-economic pressure, and tourism activity pressure in the QLMs all present a spatial distribution pattern of higher in the southeast and lower in the northwest. From a temporal perspective, most of the indicators of different subsystems show an increasing trend. The whole area of EECC in the QLMs shows an increasing trend in 85.4% of the region, while the EECC in some areas in the southeastern and northern parts shows a decreasing trend. Comparing different time periods, it is found that the EECC in the whole region shows an increasing trend from 2000 to 2010, while the proportion of areas with a decreasing trend in EECC from 2010 to 2018 reaches 67.1%. The research results can provide a scientific basis for the sustainable development of ecotourism in the QLMs and other similar regions in the world, and they further contribute to the protection of the ecological environment. [ABSTRACT FROM AUTHOR]

CYCOM 7701/7781 fiberglass epoxy fabric prepreg was used to fabricate the composite lamina specimens through medium temperature curing process. The specimens were categorized into three groups. The tensile strength of unnotched and open-hole specimens, the compressive strength of unnotched and open-hole specimens, and the compressive strength after impact were respectively tested under three conditions of cold temperature dry (CTD), room temperature dry (RTD), and elevated temperature wet (ETW). The effects of impact and open hole on typical mechanical properties of CYCOM 7701/7781 composite lamina were studied. The results show that the open-hole makes the average tensile strength decrease by about 50% under the CTD, RTD and ETW conditions, and decreases the coefficients of variation of the tensile strength. Impact damage and open-hole have similar disadvantageous effects on the average compressive strength under CTD and RTD environment conditions, which decrease the average compressive strength by about 45%-55%, while the impact damage and open-hole have different effects on the compressive strength under ETW condition. The compressive strength is decreased about 50% by the open-hole and about 30% by the impact damage under ETW condition. It is indicating that the effect of open-hole condition is more severe than that of impact damage condition under ETW condition.