To investigate the influence of polymer matrices on the tensile and impact properties of long fiber-reinforced thermoplastic (LFT) composites, composites of long basalt fiber-reinforced thermoplastic were developed in this work. Two types of polyethylene, namely 8008 and 100S, and two types of polyethylene, namely C4220 and K8303, were chosen as the matrices. The fiber volume fractions were set as 2.8%, 5.9%, 8.1%, and 10.6%. The melt flow index (MFI), crystallinity, tensile properties, impact strength, and fracture morphology of the neat polymers and the corresponding composites were tested. The composites of 8008 showed the highest tensile strength since neat 8008 showed a much higher MFI value and crystallinity. The composites of 8008 and K8303 showed a much higher tensile modulus since the neat thermoplastic showed a higher tensile modulus than the other two composites. The polymer toughness was the factor that determined whether the polymer could be toughened by fibers. Moreover, the interfacial shear strength was calculated and compared with the matrix shear strength, based on which fracture modes of the LFT were predicted. Effective methods were proposed for further improvement of the mechanical properties. The results of this paper were essential for attaining the anticipated properties when designing LFT composites.

The full-bore rupture of a buried high-pressure natural-gas pipeline can lead to detonation waves that can pose a significant threat to underground structure in the vicinity of failure location. The dominant hazards are shock wave propagation through the soil around the underground structure from buried pipeline physical explosion. In this paper, a methodology is presented to evaluate hazard areas of underground structure relating the diameter, the operating pressure, the length of pipeline, soil characteristics, the distance between buried pipeline and underground structure. An effective thermodynamic method is proposed to estimate the energy of buried pipeline physical explosion. TNT equivalent model is utilized to convert buried pipelines physical explosion energy, two simplified models are proposed, concentrated mass and linear distribution per unit length, to comprehensively describe the effective physical explosion range of the longitudinal length of the pipeline. The methodology can be readily used by practicing engineers to calculate the shock wave pressure of existing or constructing underground structure subjected to pipeline physical explosion.

The weak layer has good attenuation performance when it comes to the explosive stress wave, which can be used in protective structures. In this paper, a cement mortar specimen was designed, cast, and tested. Under inner explosion, due to the expansion of air in the explosive hole, the tensile cracks formed around the explosive hole are mainly in a damage pattern. In ordinary cement mortar, the transmittance is decreasing as the distance increases. At a distance of 8 cm to 14 cm from the explosive center, the average transmittance is 50.16%, 12 cm to 18 cm, while the average transmittance is 62.89%, increasing by 12.73%. Adding one weak layer into the cement mortar, the transmittance of one weak layer is 43.37%. The effect of increasing weak layers in short spacing is not obvious, and the transmittance of the second and third weak layer is about 80%, much less than the first layer. The softer the weak layer and the larger the wave impedance, the smaller the transmission coefficient is. The research proves that the weak layer has excellent attenuation performance when it comes to the explosive stress wave.