Elastic-plastic behavior of a semicircular frame being pressed against a rigid plane

As a simplified structural model, a semicircular frame is used to study the crashworthiness behavior of an aircraft fuselage. The quasi-static large elastic-plastic deformation of a semicircular frame in the process of its being pressed against a rigid ground is analyzed. First, based on the linear elastic assumption, the quasi-static large deformation contact process of the frame can be divided into three phases, i.e., point contact, line contact and post-buckling. By means of a shooting method, the relations between the displacement and contact force as well as the distribution of bending moment in the three phases are obtained. Then, by assuming an elastic, perfectly-plastic moment-curvature relationship for the semi-circular frame, the contact process is analyzed in detail to reveal the plastic collapse mechanism, the traveling of plastic hinge and the force-displacement relationship. In order to verify the analysis, a preliminary experiment was conducted, in which two types of half rings with clamped ends were pressed by a rigid plate. In addition, a numerical simulation is also conducted by employing ABAQUS to analyze both rectangular cross-sectional beam and I-beam. Finally, the theoretical predictions are compared with the experimental results and numerical solutions, showing that the elastic-plastic analysis can predict the contact process very well.

Rare-earth-niobate high-entropy ceramic foams with enhanced thermal insulation performance

The introduction of porous structures into high-entropy ceramics is expected to further improve its thermal insulation performance.In this work,a series of novel rare-earth-niobate high-entropy ceramic foams((Dy_(0.2)Ho_(0.2)Y_(0.2)Er_(0.2)Yb_(0.2))_(3)NbO_(7))with hierarchical pore structures were prepared by a particle-stabilized foaming method.Atomic-scale analysis reveals that high entropy causes atom displacement and lattice distortion.The high-entropy ceramic foams exhibit high porosity(90.13%-96.13%)and ultralow thermal conductivity(0.0343-0.0592 W/(m·K))at room temperature.High-entropy ceramic foam prepared by a 20 wt%slurry sintered at 1500℃has the porosity of 96.12%and extremely low thermal conductivity of 0.0343 W/(m·K).The existence of walls and secondary pores contributes to reduced thermal conductivity.There is a temperature difference of over 800℃between frontside and backside of the sample under fire resistance test.The research indicates that these as-prepared high-entropy ceramic foams are expected to be promising thermal insulation materials.

A novel classification method for mild adolescent idiopathic scoliosis using 3D ultrasound imaging

Mild adolescent idiopathic scoliosis(AIS),with Cobb<20°,was hypothesized as the right stage to intervene to prevent progression.AIS curve can be categorized into either structural or non-structural depending on the spine morphology(flexibility).Using X-ray to characterize AIS curves remains the clinical gold standard whilecompromising the risks of radiation exposure.In previous works,3D ultrasound imaging had proved the reli-ability of the coronal spinal curvature measurement This research aimed at developing a mild AIs clasificationscheme through examining spine flexibility using 3D ultrasound imaging.For the preliminary study,90 mild AIS subjects(21 M and 69 F;Age:14.5±1.7 years old;Cobb:18.2±6.4°)underwent both 3D ultrasound and X-ray scanning on the same day.For each case,a clinician measured Cobbs and denoted major curve as ground truth.Bending Asymmetry Index(BAl)was developed to indicate the presence of a possible structural curve.The curve classification was coded to a modfied Lenke classification for mild cases(m-Lenke).The results of 3D ultrasound classification were evaluated with the X-ray.It was shown that 70.1%of the subjects had identical curve clssification results and 72.0%had the correct major curve detection.Lumbar-dominated curves had distinctive performance(p=0.91,r=0.91)against others.The study demonstrated the possibility of a 3D ultrasound-based method for mild AIS curve classification.Thediscrepancies could be partially explained by the limitations of the ultrasound scanning in proximal thoracicreg ion.Subsequent studies will validate the proposed method with a larger cohort.