Binlin Ma’s research while affiliated with Air Force Engineering University and other places

Compression-compression fatigue behavior of hybrid unidirectional/woven carbon-fiber reinforced composite laminates after low-velocity impact (LVI) was studied in this paper. The paper contains two parts. Firstly, different levels of impact energy were introduced on the specimens. Impact damage modes were obtained and characterized as fiber breakages, matrix cracks, indentation and delamination. The relationships between indentation depth/damage area and impact energy were established. Secondly, compression-compression fatigue tests were conducted on the impact damaged specimens. Fatigue life degradation trends were analyzed and fatigue limit for different types of specimens was determined. Delamination areas by depth mode and amplitude mode of C-scan showed an increasing trend with the fatigue life increasing. Stiffness decreased sharply in the early and ending stages of fatigue life. However, stiffness exhibited stable or slightly decreasing rates in the mid-stage of fatigue life. A line-shaped failure cracks going through the impact point were observed in the fatigue failure specimens.

Additive manufacturing (AM) routes have brought abundant geometric defects into as-fabricated lattice materials. Researchers take it for granted that any defects in lattice struts would decrease the mechanical properties of lattice structures, which has also been a rule followed by all engineering designers. In this paper, novel design strategies of actively utilizing defects to improve the mechanical properties of BCC lattice structures are proposed. Firstly, effects of non-periodic microstructure, waving struts and missing struts on the mechanical properties (i.e. compressive modulus and initial yield strength) of BCC lattice structures are investigated through finite element analysis. Simulation results indicate that mechanical properties of the BCC lattice structures exhibited certain sensitivity to the defects. Then, strategies to enhance the performance of BCC lattice patterns by utilizing the imperfections actively are also proposed. Finally, some typical lattice specimens are fabricated and experimental tests are also conducted to validate the accuracy of design strategies. We believe that the proposed new strategy could markedly expand the design space for the development of future materials by actively utilizing the geometric defects.

The low‐velocity impact (LVI) characteristics and compression after impact (CAI) properties of aircraft composite laminates under the influence of ultraviolet (UV) radiation were studied. Firstly, 0, 30, 60, 90 days of UV radiation experiments were carried out on the specimens to analyze the characteristics of the surface topography. Secondly, LVI experiments, the impact energies of 10, 17, and 25 J, were carried out on specimens to analyze the impact response laws and the characteristics of the impact instantaneous deformation. Finally, through CAI experiments and scanning electron microscope (SEM) techniques to clarify the influence mechanism of UV radiation on the residual compressive strength of specimens. The results showed that with the increase of UV radiation time, the shrinkage and erosion phenomena of the surface matrix and the exposure degree of the surface fibers were gradually increased, and the surface fibers were completely exposed after 90 days of radiation. At the same impact energy, with longer radiation time, the peak force gradually decreased (from 8673.86 to 7851.68 N at 17 J), the absorbed impact energy (from 9.48 to 11.13 J at 17 J) and maximum displacement (from 4.1 to 4.73 mm at 17 J) increased, the depth of pit on the impact surface decreased (from 0.213 to 0.14 mm at 17 J), and the internal damage projection area increased (from 906.68 to 1158.66 mm ² at 17 J). The compression damage of the specimens not exposed to/ exposed to UV radiation was mainly fiber cracking/interlayer delamination, respectively. Highlights Ultraviolet (UV) radiation makes the matrix of surface shrink, the fibers exposure increase. The Stage II has obvious oscillation phenomenon in four stages of the low‐velocity impact process. With prolonged UV radiation, the projected area of internal damage expands. The residual compressive load increases with the increase of UV radiation time.

This paper proposes a flexible eddy current TMR (FEC-TMR) sensor to monitor the internal crack of metal joint structures. First, the finite element model of the FEC-TMR sensor is established to analyze the influence of the sensor’s crack identification sensitivity with internal crack propagation at different depths and determine the optimal location and exciting frequency of the sensor. Then, the optimal longitudinal spacing and exciting frequency of the sensor are tested by experiment. The experimental results are consistent with the simulation results, which verify the correctness of the simulation model. Finally, the experiment is carried out for internal cracks of different depths to verify that the sensor can monitor internal cracks, and the crack identification sensitivity gradually decreases with the increase in the depth of the crack from the surface.

Truss-lattices have wide application prospects in various important fields owing to their superior mechanical properties and energy absorption characteristics. In this paper, two typical truss-lattice materials (i.e. bending-dominated body-centred cubic (BCC) and stretch-dominated Octet architectures) were designed with enhanced mechanical properties and tunable anisotropy. The elastoplastic properties and large strain response were both investigated numerically and experimentally. Numerical results showed that a relative larger stiffness characteristic could be harvested when the shape parameter was chosen between 0.2 and 0.3, and the anisotropy degree could also be controlled through the shape parameter. Large strain multi-cell simulations also demonstrated the enhanced plastic properties and energy absorption characteristics of the designed architectures. The numerical findings were then confirmed through the uniaxial compression experiments on the 316L stainless steel truss-lattices specimens fabricated by the Selective Laser Melting (SLM) process. This study would broaden the design idea for the 3D truss-lattices with enhanced mechanical performance and tunable anisotropy, which may of great potential in engineering applications.

The hole edge of a metal structure is the most likely crack position in an aircraft structure. The quantitative monitoring of a hole-edge crack is important for structural health monitoring. Therefore, this paper presented a grating thin-film sensor based on the potentiometric method. Firstly, the anodic oxidation process was used to prepare thin film on 2A12-T4 aluminum alloy matrix to prevent the aluminum alloy matrix from interfering with the monitoring signal of the sensor. Then the DC superimposed pulsed bias arc ion plating technique was used to prepare the grating thin-film sensor on the surface of the specimen. The output characteristics of the grating thin-film sensor are obtained with its finite element model, and the factors affecting the sensitivity of the sensor are analyzed. Finally, the fatigue crack monitoring tests were carried out to verify the quantitative monitoring capability of the grating thin film sensor. The experimental results show that it is feasible for the grating thin-film sensor to quantitatively monitor the fatigue crack at the hole edge of an aircraft metal structure.