Experimental damage tolerance evaluation of thick fabric carbon/epoxy laminates under low-velocity and high-velocity impact and compression-after-impact

Impact experiments of thick fabric carbon/epoxy laminate specimens, with small thickness ratio, are conducted at distinct energy levels and thicknesses to characterise the damage process. These specimens and loading conditions are representative of a new generation of critical structural components in aviation, such as wing spars, landing gear beams and fittings, that are increasingly being made entirely from composites. The tests address the need to better understand the damage process for specimens with a small thickness ratio since existing experimental impact data for large thickness ratio (thin laminates) may not be directly applicable. Two energy levels, two different fabric layups and two impact methods (drop-weight and gas-cannon) were used. Data from high-speed cameras were processed in a novel way, providing the force during impact. C-scans and micrographs were used to characterise damage. The results show that specimens with a thickness ratio of 5 (20 mm thick) experience more bending compared to specimens with a ratio 2.5 (40 mm thick). For gas-cannon impacts, this results in a higher delaminated area. The drop-weight impacts show almost no differences in damage size for the thickness range analysed. The influence of layup on the global impact response is negligible, but locally it can result in significant variations in dent depth. The dent depth scales linearly with the impact energy and the delaminated area linearly with the impact velocity. There is no clear correlation between the compression-after-impact failure mechanisms and the residual strength. Impact damage, at the current energy levels, showed a minimal reduction of residual strength.

The Fabrication and Mechanical Properties of Laminated ZrB2-Mo5SiB2 Ceramics with an Mo-Mo5SiB2 Interlayer

The excellent physical and chemical properties of ultra-high temperature ceramics make them suitable for many high-temperature structural components, while their poor toughness and high sintering temperature become key limitations to their application. Laminated toughening has long been considered an effective toughening method to improve the mechanical properties of ceramics. In this study, laminated ZrB2-Mo5SiB2 ceramics with an Mo-Mo5SiB2 interlayer were fabricated by tape casting and hot press sintering at 1900 °C for 2 h. Different layer thickness ratios between the matrix layer and the interlayer were designed to illustrate the toughening mechanism. Both the fracture toughness and flexural strength of the laminated ceramics showed a trend of first increasing and then decreasing with the increase of the layer thickness ratio. High fracture toughness (9.89 ± 0.26 MPa·m1/2) and flexural strength (431.6 ± 15.1 MPa) were obtained when the layer thickness ratio was 13. The improvement in fracture toughness of the laminated ceramics could be attributed to the generation of the residual stress, the deflection and the bifurcation of the cracks. Residual stress that developed in the laminated ceramics was also evaluated.

Parametric influence of magneto elasticity, initial stresses, porosity and thickness ratio on the phase and attenuation traits of SH-waves

The present study is devoted to investigate the traversal of shear horizontal wave (SH-waves) in an initial-stressed fluid saturated porous stratum bounded between an initial-stressed magneto-elastic upper stratum and an initial-stressed elastic substrate. We have obtained the exact solution of the governing equations and explained in detail for various effective parameters. The displacement relation is developed with the help of Maxwell’s fundamental equations and Maxwell’s tensor. The impact of diverse parameters such as initial stress, porosity, magneto-elasticity, thickness ratio of attenuation coefficient and phase velocity of SH-wave has been discussed extensively by means of graphical depictions. Results indicate that such parameters possess a great positive impact on attenuation coefficient. This model contains a huge potential to deal with many commercial and industrial applications in Geo-technical, earthquake engineering and Geophysics.

Clinical and Laboratory Markers in Determination of Treatment Modalities and Short-Term Prognosis in Patients with Traumatic Acute Subdural Hematoma: Original Study

Objective In patients with traumatic acute subdural hematoma (ASH), it has not been yet fully elucidated which patients can benefit from surgery or from clinical follow-up. This study was constructed to predict treatment modality and short-term prognosis in patients with ASH using their clinical, radiological, and biochemical laboratory findings during admission to hospital. Methods Findings of patients with ASH determined on their CT scan between 2015 and 2018 were evaluated. Patients were grouped in terms of ASH-FOL (patients followed-up without surgery, n = 13), ASH-OP (patients treated surgically, n = 10), and ASH-INOP (patients considered as inoperable, n = 5) groups. They also were divided into “survived (n = 14)” and “nonsurvived (n = 14)” groups. Results ASH developed as a result of fall from a height in 15 patients and traffic accidents in 13 patients. In deciding for surgery, it was determined that Glasgow coma scale (GCS) scores < 8, midline shift (MLS) level > 5 mm, MLS-hematoma thickness ratio > 0.22, leukocyte count > 12730 uL, and presence of anisocoria could be used as predictive markers. It was determined that GCS scores < 8, hematoma thickness value > 8 mm, and the presence of anisocoria could be considered as biomarkers in prediction of mortality likelihood. Conclusion It could be suggested that GCS scores, MLS level, MLS-hematoma thickness ratio, presence of anisocoria, and leukocyte count value could help in determination of the treatment modality in patients with ASH. Additionally, GCS scores, hematoma thickness value, and presence of anisocoria could each be used as a marker in the prediction of early-stage prognosis and mortality likelihood of these patients.

Parametric study on the influence of material properties and geometry on the thermally induced bistability of composite laminates

This paper presents a parametric study on the key parameters that control the thermally induced bistability of cross-ply laminates. The influence of the material properties including the moduli of elasticity and the thermal expansion coefficients and the laminate’s geometry including the aspect ratio (AR) and the width-to-thickness ratio are investigated. The unsymmetric [Formula: see text] and the antisymmetric [Formula: see text] cross-ply laminates are investigated. Five key parameters are varied: the number of plies, the width-to-thickness ratio, the laminate’s aspect ratio, the ratio of the moduli of elasticity, and the ratio of the thermal expansion coefficients of the lamina. The laminate is assumed flat at the cured temperature and a uniform temperature gradient is applied until it is reduced to the room temperature. For each set of parameters, the stable equilibrium shapes of the laminate are obtained using a Ritz model. The ABAQUS finite element package is used to validate the model and an excellent agreement is obtained. Results that show the variation of the curvatures with the width-to-thickness ratio and the onset of the bistability for a variety of parameters are presented. The ratio of the moduli of elasticity and the thermal expansion coefficients significantly affect the critical width-to-thickness ratio at which the laminates become bistable. The unsymmetric laminates show bistability at a lower width-to-thickness ratio compared with the antisymmetric laminates. The results also show that the higher the aspect ratio, the lower the critical width-to-thickness ratio for stability for both laminates.

Lateral-Torsional Buckling Analysis for Doubly Symmetric Tubular Flange Composite Beams with Lateral Bracing under Concentrated Load

Tubular flange composite beams are increasingly applied in modern bridge structures. In order to investigate the overall stability behavior of doubly symmetric tubular flange composite beams with lateral bracing under concentrated load, the analysis of elastic lateral-torsional buckling is conducted by the energy variation method. The analytical solution of critical moment of doubly symmetric tubular flange composite beams with lateral bracing is obtained. Meanwhile, the simplified calculation formula of critical moment is fitted by 1stOpt software based on 26,000 groups of data, and the accuracy is verified by the finite element method. It is found that, the critical moment rises obviously with increasing lateral bracing stiffness, and adding lateral bracing to doubly symmetric tubular flange composite beams is beneficial to improve the overall stability in engineering practice. Finally, the influence of several parameters including concrete strength, span, steel ratio of flange and height-thickness ratio of web are studied. The results show that the concrete strength and the web height-thickness ratio have a weak influence on critical moment of elastic lateral-torsional buckling, while the influence of span-depth ratio and flange steel ratio is very significant.