Carbon fiber-reinforced composite materials are widely employed in aircraft structures due to their high specific strength and high specific modulus. However, the poor impact resistance of carbon fiber reinforced composites creates challenges for aircraft design and maintenance. The introduction of a layer of glass fibers in the hybrid composites can effectively improve the impact performance of the composite laminate. In this work, finite element models for low-velocity impact of carbon fiber laminate and glass fiber laminate are established and validated. A VUMAT subroutine in Abaqus is implemented to evaluate the progressive damage of the composite materials, and a cohesive-zone model is employed to simulate the interface failure behavior. The impact resistance of hybrid composite laminates is systematically studied based on the results of the finite element simulation. Ten different hybrid configurations are studied and compared with a composite laminate having a single type of fiber reinforcement. The numerical results for the global mechanical response, damage modes and characteristics are extracted and systematically discussed. The results suggest that laminates having carbon fiber layers on the top and bottom surfaces with glass fiber layers between them perform the best in terms of energy absorption. When the glass fiber layers are used for the top and bottom surfaces with carbon fiber layers as the core, the presence of a carbon fiber layer with a ±45 ° orientation can help to reduce the damage area.

The mechanical characterization of textile composites is a challenging task, due to their nonuniform deformation and complicated failure phenomena. This article introduces a three-dimensional mesoscale finite element model to investigate the progressive damage behavior of a notched single-layer triaxially-braided composite subjected to axial tension. The damage initiation and propagation in fiber bundles are simulated using three-dimensional failure criteria and damage evolution law. A traction-separation law has been applied to predict the interfacial damage of fiber bundles. The proposed model is correlated and validated by the experimentally measured full field strain distributions and effective strength of the notched specimen. The progressive damage behavior of the fiber bundles is studied by examining the damage and stress contours at different loading stages. Parametric numerical studies are conducted to explore the role of modeling parameters and geometric characteristics on the internal damage behavior and global measured properties of the notched specimen. Moreover, the correlations of damage behavior, global stress-strain response, and the efficiency of the notched specimen are discussed in detail. The results of this paper deliver a throughout understanding of the damage behavior of braided composites and can help the specimen design of textile composites.

SPAD (single-photon avalanche diode) arrays are single-photon sensors, which enable photon counting and unparalleled time-resolved imaging. In this paper, we will detail the architecture and characteristics of three representative SPAD arrays, implemented in standard CMOS technologies and targeted to a range of applications such as biophotonics, basic sciences, and engineering. Two sensors feature a high-performance pixel and enable time-gated and TCSPC operation, respectively. The third sensor is a line array whose pixels are coupled on a one-To-one basis with an FPGA for flexible data acquisition and processing.