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This paper addresses a simplified analytical method for evaluating the impact responses of the stiffeners in a ship side shell subjected to head-on collision by a bulbous bow. The stiffeners are classified as the "central stiffener" and the "lateral stiffener" according to their relative position to the bulbous bow. In analytical predictions, it is assumed that the flexural bending of the central stiffener and plate occurs simultaneously. However, the deformation mode of the central stiffener outside the indenter contact region is simplified as linear to derive its deformation resistance. The curved deformation mode of the lateral stiffener is proposed to calculate the deformation resistance and to consider the interaction effect with the plate, which can cause the plate to fracture earlier. Model tests with three specimens (one unstiffened plate for reference and two stiffened plates) quasistatically punched by a conical indenter are performed to validate the proposed analytical method. Resistance-penetration curves and damage shapes for the three specimens are obtained. The experimental results illustrate the effects of the stiffeners on the deformation resistance and fracture initiation of the stiffened plate and the influence of stiffener tripping on the lateral resistance. Moreover, the experimental and analytical predicted results correspond well, suggesting that the proposed analytical method can accurately predict the crashworthiness of a ship side shell subjected to bulbous bow collision. [ABSTRACT FROM AUTHOR]

This paper aims to investigate the low-velocity impact response and post-impact flexural behaviour of hybrid sandwich structures consisting of carbon fibre-reinforced polymer (CFRP) face sheets and aluminium alloy corrugated cores. A combined experimental and numerical study is carried out over a range of impact energies and impact sites to evaluate the effects of the abovementioned factors on the impact damage and residual flexural strength. Low-velocity impact tests are performed to investigate the impact resistance of such structures with respect to impact load, absorbed energy and failure mode. Subsequently, three-point bending tests are conducted to determine and quantify the effects of impact damage on the residual properties of post-impact sandwich structures. Meanwhile, a procedure to numerically simulate the low-velocity impact tests and residual flexural strength tests of sandwich structures is developed by the VUMAT subroutine in ABAQUS/Explicit. Reasonably good agreement is achieved when comparing the impact response and flexural behaviour between experimental measurements and numerical predictions. These studies reveal that the damage depends on the impact energy and impact location. The residual flexural strength decreases significantly even though the impact energy is lower than 10 J, while there is a slight reduction with a further increase in the impact energy. [ABSTRACT FROM AUTHOR]

The carbon fiber reinforced composite reentrant honeycomb structures with different gradient distributions of wall thickness were manufactured by mold hot pressing and bonding technology. The dynamic responses of composite gradient reentrant honeycomb structures under local impact load were investigated. The impact process and failure behavior of composite gradient reentrant honeycomb structures under local impact load were obtained through the foam aluminum projectile impact experiment. The influence of wall thickness gradient form on the impact resistance of composite reentrant honeycomb structure was analyzed. The results showed that the wall thickness gradient setting of the reentrant honeycomb structure could reduce the maximum transverse deformation of the rear panel, and improve the anti-impact ability of the structure compared with homogeneous reentrant honeycomb structure. In addition, compared with the positive gradient reentrant honeycomb structure, the negative reentrant honeycomb structure had better impact resistance, and the impact resistance advantage became more obvious with the increase of the impact strength. The finite element model of composite gradient reentrant honeycomb structure under local impact load was presented, and the dynamic responses and failure modes of the numerical simulation results were compared with that of the experimental results. • A novel composite reentrant honeycomb structure is designed and fabricated. • The anti-impact properties of composite reentrant honeycomb structure were explored and analyzed by experiment and finite element analysis. • The effect of wall thickness gradient form on the impact response was analyzed and revealed. • The failure mechanism of composite gradient reentrant honeycomb structure was analyzed and obtained. [ABSTRACT FROM AUTHOR]

Abstract This paper systematically investigates the low-velocity impact response and resulting damage behavior of aluminum honeycomb sandwich structures with carbon fiber reinforced plastic (CFRP) face sheets by combining the experimental and numerical methods. Low-velocity impact tests are conducted to determine and quantify the effects of structural parameters, such as face sheet thickness, cell wall thickness, honeycomb core height and hexagon side length, on the impact load, energy absorption, and failure mode. To further elucidate the impact behavior, a user VUMAT subroutine is developed to predict the progressive failure behavior of composite face sheets. Numerical simulation is performed to characterize the impact response and explore the deformation/failure mechanisms. The predicted impact load, energy absorption, contact time and failure mode agree well with measured counterparts. These studies reveal the face sheet thickness has particularly significant influence on the impact resistance performance of honeycomb structures. Cell wall thickness and side length of honeycomb core have notable effect on the impact load and structural stiffness of such structures, while which do not play a great role in energy absorption. Increase in core height has comparatively little effect on initial stiffness and energy absorption but makes the second peak loads decreasing for the perforation cases. Highlights • Low-velocity impact response of honeycomb sandwich structures is studied. • VUMAT is developed to explore damage state and failure mechanism of composite. • Impact response and damage behavior are seriously affected by structural parameters. • Face sheet thickness has significant influence on the impact resistance performance. • Cell wall thickness and core side length have notable influence on the impact load. [ABSTRACT FROM AUTHOR]

In present study, the foam-filled composite double-arrow auxetic structures were obtained by the mold hot pressing method, bonding technology and stirring foaming process. The ballistic impact tests of the foam-filled composite double-arrow auxetic structure were carried out, and the effect of foam filling on the ballistic impact response of the composite double-arrow auxetic structure was analyzed. The ballistic impact test results indicated that the ballistic limit velocity of the foam-filled double-arrow auxetic structure with the relative density of 16.66% was 121.30 m/s. With the increase of the incident kinetic energy of the projectile, the specific energy absorption of the foam-filled auxetic structure increased first and then decreased, and remained near the horizontal line of 550 J/kg at last. Compared to unfilled auxetic structure, the ballistic limit velocity of foam-filled auxetic structure increased by 6.12% and the energy absorption property of foam-filled auxetic structure was improved. The ballistic impact performances of foam-filled composite double-arrow auxetic structures were studied by finite element method. The simulation results of foam-filled auxetic structure with RD=16.66% were in good agreement with the experimental results. The simulation results demonstrated that the ballistic limit velocities of foam-filled composite auxetic structures with relative densities of 9.08%, 16.66% and 23.06% were 86.74 m/s, 120.60 m/s and 152.80 m/s, respectively. Furthermore, the increase of relative density had a positive effect on improving the anti-penetration performance of foam-filled composite auxetic structures. • A novel foam-filled composite double-arrow auxetic structure was fabricated. • The ballistic impact experiments were conducted to evaluate the impact properties. • The effect of foam filling on the ballistic impact response was analyzed. • The finite element model was used to simulate the ballistic impact process. [ABSTRACT FROM AUTHOR]

A novel composite double-arrow auxetic structure was designed and fabricated in this paper. The ballistic impact experiments were conducted using one stage gas gun to study the effects of the relative density on the impact responses and failure mechanism. The impact process of the projectile was recorded by a high-speed camera. The ballistic limit velocities, damage area and failure mechanism of composite double-arrow auxetic structure with different relative densities were compared and analyzed. The anti-penetration performances of composite double-arrow auxetic structure were evaluated and discussed based on the experimental results. In order to simulate and reveal the damage evolution process, the finite element model was used to simulate the ballistic impact process of composite double-arrow auxetic structure. The ballistic limit velocities and failure modes of the simulation results were compared with that of the experimental results. The comparison indicated that the simulated results were in agreement with the experimental results. • A novel composite double-arrow auxetic structure was designed and fabricated. • The ballistic impact experiments were conducted study the impact responses. • The anti-penetration performances of the structure were evaluated and discussed. • The finite element model was used to simulate the ballistic impact process. [ABSTRACT FROM AUTHOR]