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The tail drive shaft is easily hit by the ground antiaircraft machine gun in low-altitude helicopter combat, resulting in projectile penetration damage and directly jeopardizing the helicopter’s safety during flight. The projectile penetration damage will cause elastic–plastic deformation and failure damage to the tail drive shaft, and excite high-frequency stress waves suitable for projectile impact monitoring. To examine the effects of different impact parameters on the stress wave characteristics and damage from the tail drive shaft during projectile impact, the LS-DYNA is used to establish a dynamic model of projectile impact on the tail drive shaft. The passive monitoring experiment of projectile impact on the tail drive shaft is carried out based on the PZT piezoelectric sensor. It is concluded that both methods can obtain reliable stress wave signals and damage conditions through the comparison of experimental and simulation results. Then, the wavelet transform and short-time Fourier transform three-dimensional time–frequency are used to select the best frequency band for extracting the stress wave eigenvalues, along with the statistics and analysis of the stress wave characteristic values and damage degree under different impact parameters. The results show that the impact stress waveforms and high-frequency components are significantly different with the change in projectile impact parameters. There are significant differences among different impact parameters on the first trough amplitude, the two peak time intervals, the kurtosis factor, and the bullet hole damage generation laws. The functional relationship between the projectile impact parameters and the characteristic parameters of the stress wave, as well as the damage degree, are established. The research conclusion can provide theoretical reference and data support for projectile impact monitoring and damage assessment of the helicopter tail drive shaft.

The impact damage of an Al₂O₃-coated soda-lime glass under tensile and compressive stress conditions was investigated by an impact test using a steel ball (2mm dia.). The size of the glass specimens was 40×40×5(mm). In order to change the porosity percent of each specimen, the target distance was set at 120mm and 70mm. Also, the effect of the thickness of the coating layer was shown by two amounts (100 μm and 50 μm). The velocity of the steel balls was set between 30 and 60m/s. After the impact test, the crack patterns and lengths were measured using a stereo-microscope. The tensile and compressive specimens were prepared by inflation and deflation of air pressure within a pressure vessel. It was confirmed that the crack length of the glass under tensile stress was longer than that of glass under compressive stress. Also, the optimum conditions were a target distance of 70mm and 100 μm of a coating thickness, thus resulting in a minimization of porosity percent and area.

Honeycomb composites are now fairly widely used in civilian and military aircraft structures. Common defects found in these materials are delaminations by impact damage and their presence will lead to structural weaknesses which could lead failure of the airframe structures. It is important to develop effective non-destructive testing procedures to identify these defects and increase the safety of aircraft travel. This paper describes the detection technique of impact damage defect using thermography and ESPI. The results obtained with the two techniques are compared with ultrasonic C-scan testing. The investigation shows that both imaging NDT methods are able to identify the presence of artificial defect and impact damage. The adoption of the thermography allowed significant advantages in inspection condition, and gives smaller error in quantitative estimation of defects.

Composites are vulnerable to the impact damage by the collision as to the thickness direction, because composites are being manufactured by laminating the fiber. The understanding about the retained strength after the impact damage of the material is essential in order to secure the reliability of the structure design using the composites. In this paper, we have tried to evaluate the motion of the material according to the kinetic energy and potential energy and the retained strength after impact damage by testing the free fall test of the basalt fiber reinforced composite in the limelight as the environment friendly characteristic.

This work used short carbon fibers (SCFs) of different lengths to manufacture epoxy bulk mold compound (BMC) composites. Drop-weight-impact tests were performed on the intact carbon-fiber-reinforced-polymers (CFRPs) laminates to generate artificial damage. The damaged CFRP laminates were then repaired using the SCF-BMC composites. Compression after impact (CAI) tests were conducted to measure the compressive strength of the repaired laminates. Tensile properties and compressive properties of the SCF-BMC composites were also measured. The results show that 48-mm carbon fibers result in the largest tensile modulus, tensile strength, and compressive strength, while 12-mm carbon fibers result in the largest compressive modulus. CAI test results show that the compressive strength of the repaired laminate can be restored to 80.3% of that of the undamaged laminate. Therefore, SCF-BMC composites significantly contribute to repairing damaged composite laminates.