High-velocity impact study of an advanced ceramic using finite element model coupling with a machine learning approach

A numerical approach combining finite element modeling and machine learning is used to inform the material performance of an alumina ceramic tile undergoing high-velocity impact. In this study, the alumina ceramic tile is simulated by incorporating a user-defined Johnson–Holmquist–Beissel (JHB) material model within the framework of smoothed particle hydrodynamics (SPH) in LS-DYNA finite element software. The implementation of the JHB model is verified by comparing equivalent stress–pressure responses through a single element simulation test. After implementation, the computational framework is simulated across our chosen range of conditions by matching the results from both plate impact experiments and ballistic testing from the literature. The computational model is then used to generate training data sets for an artificial neural network (ANN) to predict the residual velocity and projectile erosion for an alumina ceramic tile undergoing high-velocity impact in the SPH framework. The ANN is then used to perform a sensitivity analysis involving exploring the effect of mechanical properties (e.g., strength and shear modulus) and impact simulation geometries (e.g., thickness of ceramic tile) on material performance (i.e., residual projectile velocity and erosion). Overall, this study shows the capability of the FEM-ANN approach in studying the high-velocity impact on ceramic tiles and is applicable to guide the structural-scale design of ceramic-based protection systems

Review of Maxillary Expansion Appliance Activation Methods: Engineering and Clinical Perspectives

Objective. Review the reported activation methods of maxillary expansion devices for midpalatal suture separation from an engineering perspective and suggest areas of improvement. Materials and Methods. A literature search of Scopus and PubMed was used to determine current expansion methods. A U.S. and Canadian patent database search was also conducted using patent classification and keywords. Any paper presenting a new method of expansion was included. Results. Expansion methods in use, or patented, can be classified as either a screw- or spring-type, magnetic, or shape memory alloy expansion appliance. Conclusions. Each activation method presented unique advantages and disadvantages from both clinical and engineering perspectives. Areas for improvement still remain and are identified in the paper

Carbapenem-resistant Citrobacter spp. isolated in Spain from 2013 to 2015 produced a variety of carbapenemases including VIM-1, OXA-48, KPC-2, NDM-1 and VIM-2

Objectives: There is little information about carbapenemase-producing (CP) Citrobacter spp.We studied the molecular epidemiology and microbiological features of CP Citrobacter spp. isolates collected in Spain (2013-15). Methods: In total, 119 isolates suspected of being CP by the EUCAST screening cut-off values were analysed. Carbapenemases and ESBLs were characterized using PCR and sequencing. The genetic relationship among Citrobacter freundii isolates was studied by PFGE. Results: Of the 119 isolates, 63 (52.9%) produced carbapenemases, of which 37 (58.7%) produced VIM-1, 20 (31.7%) produced OXA-48, 12 (19%) produced KPC-2, 2 (3.2%) produced NDM-1 and 1 (1.6%) produced VIM- 2; 9 C. freundii isolates co-produced VIM-1 plus OXA-48. Fourteen isolates (22.2%) also carried ESBLs: 8 CTX-M-9 plus SHV-12, 2 CTX-M-9, 2 SHV-12 and 2 CTX-M-15. Fifty-seven isolates (90.5%) were C. freundii, 4 (6.3%) were Citrobacter koseri, 1 (1.6%) was Citrobacter amalonaticus and 1 (1.6%) was Citrobacter braakii. By EUCAST breakpoints, eight (12.7%) of the CP isolates were susceptible to the four carbapenems tested. In the 53 CP C. freundii analysed by PFGE, a total of 44 different band patterns were observed. Four PFGE clusters were identified: cluster 1 included eight isolates co-producing VIM-1 and OXA-48; blaVIM-1 was carried in a class 1 integron (intI-blaVIM-1 - aacA4-dfrB1-aadA1-catB2-qacE¿1/sul1) and blaOXA-48 was carried in a Tn1999.2 transposon. Conclusions: We observed the clonal and polyclonal spread of CP Citrobacter spp. across several Spanish geographical areas. Four species of Citrobacter spp. produced up to five carbapenemase types, including coproduction of VIM-1 plus OXA-48. Some CP Citrobacter spp. isolates were susceptible to the four carbapenems tested, a finding with potential clinical implications

A comparative finite element analysis of maxillary expansion with and without midpalatal suture viscoelasticity using a representative skeletal geometry

AbstractThe goal of this investigation was to adapt and incorporate a nonlinear viscoelastic material model representative of the midpalatal suture’s viscoelastic nature into finite element analysis simulations of maxillary expansion treatment. Step-wise displacements were applied to a partial skull geometry to simulate treatment using an expansion screw appliance. Four simulation cases were considered for the midpalatal and intermaxillary sutures: 1. Neglecting suture tissue; 2. Linear elastic properties; 3. Viscoelastic properties; 4. A fused intermaxillary and viscoelastic midpalatal suture. Results from simulations indicated that removal of suture tissue and inclusion of viscoelastic properties resulted in the same maxillary displacement following 29 activations of 0.125 mm applied directly to the maxilla; however, assuming a fused intermaxillary suture significantly changed maxillary displacement patterns. Initial stress results within the suture complex were significantly influenced by the inclusion of suture viscoelasticity as compared to linear elastic properties. The presented study demonstrates successful incorporation of suture viscoelasticity into finite element analysis simulations of maxillary expansion treatment, and elucidates the appropriateness of various suture material property assumptions depending desired research outcomes.</jats:p

Computational finite element modeling of stress-state-and strain-rate-dependent failure behavior of ceramics with experimental validation

This study investigates the stress-state- and strain-rate-dependent behavior of CeramTec ALOTEC 98% alumina (Al2O3) ceramic through experimentally validated finite element (FE) modeling. As the constitutive material model, a rate-dependent viscosity-regularized phenomenological model (JH2-V model) was implemented through a VUMAT subroutine in ABAQUS software. The FE model was informed and validated with the data for indirect tension and compression–shear tests under dynamic rates both quantitatively (i.e., stress–strain histories and lateral strain–axial strain curves) and qualitatively (i.e., manifestation and accumulation of damage). The validated model was leveraged to study the effect of the JH2-V model regularization parameters, mesh sensitivity, and bulking across different stress states. Additionally, by modeling the compression–shear specimen with different angles, the effect of shear on the material response was quantitatively investigated through the definition of a volumetric average damage parameter and shear strain history. Altogether, the outcomes of this study have implications for the computational design and development of ceramic-based structures in higher-scale applications (e.g., impact)

Density, Microstructure, and Strain‑Rate Effects on the Compressive Response of Polyurethane Foams

Background A better understanding of the efect of density, microstructure, and strain rate on the mechanical response of polymeric foam materials is needed to improve their performance. Objective The objective of this paper is to study the combined infuence of density, microstructure, and strain-rate on the compressive stress-strain response of polymeric foams. Methods Microstructural morphological parameters (e.g., pores sizes and wall thicknesses) have been quantifed using Micro X-ray tomography and MATLAB-based techniques. Polymeric foam samples were examined under uniaxial compression loading at quasistatic (0.001 to 0.1s−1), intermediate (1 to 250s−1), and dynamic strain rates (3200 to 5700s−1 ). All experiments were coupled with high speed cameras to measure strain using 2D digital image correlation, and to visualize deformation. Results The variation of the mechanical properties across alldensities (e.g., elastic modulus and collapse stress) are found to behave in a powerlawfashion with respect to strain rate. A comprehensive data set across a varied rangeof densities and strain rates, especially intermediate strain rates, is lacking in previous research, and generalized phenomenological relationships developed in this paper topredict combined infuences of density, microstructure, and strain-rate over variedrange of materials are important contributions of this work. Conclusions The results showed that the power-law relationships act as a good predictor for the prediction of mechanical properties and elastic response, and as an indicator for damage mechanisms in these polymeric foams