ADAPTATION OF THE TSAI-HILL CRITERION FOR THE STUDY OF THE BEHAVIOR OF MASONRY ARCHES ADAPTATION OF THE THAI-HILL CRITERION FOR THE STUDY OF THE BEHAVIOR OF MASONRY ARCHES: COMPARISON BETWEEN MASOMODEL, EXPANDED MICROMODEL AND DETAILED MICROMODEL

Since the beginning of the structural analysis of masonry structures, it has been sought to know their behavior taking into account the influence of the different elements that make it up, evolving the structural analysis of masonry arches to analyze the fracto-mechanical behavior of the masonry. This article presents the adaptation of the Tsai-Hill failure criterion for orthotropic materials, for the study of masonry arches. Implementing the adaptation in a VUSFLD subroutine of ABAQUS in Fortran programming language. This subroutine has been validated in view of the failure of the mortar, and the effect of considering mortar in the analysis of a masonry arch. The subroutine implemented in a masomodel allows observing its contribution to the bearing capacity of an arch. Key Words: Masonry Arch; ABAQUS subroutine; failure Criterion; Mortar; structural analysis; Tsai-Hill failure criterion

A Finite Element Method to Predict the Mechanical Behavior of a Pre-Structured Material Manufactured by Fused Filament Fabrication in 3D Printing

In this paper, a numerical method is proposed to simulate the mechanical behavior of a new polymeric pre-structured material manufactured by fused filament fabrication (FFF), where the filaments are oriented along the principal stress directions. The model implements optimized filament orientations, obtained from the G code by assigning materials references in mesh elements. The Gauss points are later configured with the physical behavior while considering a homogeneous solid structure. The objective of this study is to identify the elastoplastic behavior. Therefore, tensile tests were conducted with different filament orientations. The results show that using appropriate material constants is efficient in describing the built anisotropy and incorporating the air gap volume fraction. The suggested method is proved very efficient in implementing multiplex G code orientations. The elastic behavior of the pre-structured material is quasi-isotropic. However, the anisotropy was observed at the yield point and the ultimate stress. Using the Hill criterion coupled with an experimental tabular law of the plastic flow turns out to be suitable for predicting the response of various specimens.

NUMERICAL INVESTIGATION ON THE FUSELAGE AIRFRAME OF LSU 05 NG AIRCRAFT

In this paper, numerical investigation on the fuselage structure of LSU 05 NG was carried out. This fuselage is designed to carry the payload up to 30 kg. Statical numerical analysis using finite element method was done using Simulia Abaqus. The fuselage structure that has been design consists of frame, longeron, and skin that can also be semi-monocoque structure. This airframe use combination of balsa and GFRP type of composite as the material. There are three load case: take-off condition, cruise condition, and landing condition. Tsai-hill failure criteria is used to investigate the strength of the composite structure due to the load that applied. Maximum stress from this calculation is 48 Mpa at the ground condition (take-off and landing) while the cruise stress analysis is 16 Mpa. The maximum tsai-hill criterion is 0,83. With such simulation results it can be said that the fuselage structure is still safe when operated and can also be optimized for several components so that the weight of the aircraft can be reduced.

Monotonic Tension-Torsion Experiments and FE Modeling on Notched Specimens Produced by SLM Technology from SS316L

The aim of this work was to monitor the mechanical behavior of 316L stainless steel produced by 3D printing in the vertical direction. The material was tested in the “as printed” state. Digital Image Correlation measurements were used for 4 types of notched specimens. The behavior of these specimens under monotonic loading was investigated in two loading paths: tension and torsion. Based on the experimental data, two yield criteria were used in the finite element analyses. Von Mises criterion and Hill criterion were applied, together with the nonlinear isotropic hardening rule of Voce. Subsequently, the load-deformation responses of simulations and experiments were compared. Results of the Hill criterion show better correlation with experimental data. The numerical study shows that taking into account the difference in yield stress in the horizontal direction of printing plays a crucial role for modeling of notched geometries loaded in the vertical direction of printing. Ductility of 3D printed specimens in the “as printed” state is also compared with 3D printed machined specimens and specimens produced by conventional methods. “As printed” specimens have 2/3 lower ductility than specimens produced by a conventional production method. Machining of “as printed” specimens does not affect the yield stress, but a significant reduction of ductility was observed due to microcracks arising from the pores as a microscopic surface study showed.

Optimum Design of Infinite Perforated Orthotropic and Isotropic Plates

In this study, an attempt was made to introduce the optimal values of effective parameters on the stress distribution around a circular/elliptical/quasi-square cutout in the perforated orthotropic plate under in-plane loadings. To achieve this goal, Lekhnitskii’s complex variable approach and Particle Swarm Optimization (PSO) method were used. This analytical method is based on using the complex variable method in the analysis of two-dimensional problems. The Tsai–Hill criterion and Stress Concentration Factor (SCF) are taken as objective functions and the fiber angle, bluntness, aspect ratio of cutout, the rotation angle of cutout, load angle, and material properties are considered as design variables. The results show that the PSO algorithm is able to predict the optimal value of each effective parameter. In addition, these parameters have significant effects on stress distribution around the cutouts and the load-bearing capacity of structures can be increased by appropriate selection of the effective design variables. The main innovation of this study is the use of PSO algorithm to determine the optimal design variables to increase the strength of the perforated plates. Finite element method (FEM) was employed to examine the results of the present analytical solution. The results obtained by the present solution are in accordance with numerical results.

COMPARISON OF FAILURE CRITERIA FOR WOOD IN TENSILE-SHEAR STRESS STATE

An orthotropic failure criterion enhancing the Lourenco's criterion by a shear strength multiplier and a maximum shear strength upper bound has been recently proposed and validated for timber under tensile and shear loading by the authors. The paper discusses its applicability for predicting strength in comparison with Tsai-Hill criterion, Hankinson's and Hyperbolic formula applying the two above mentioned enhancements of the Lourenco's criterion. Experimental data available in the literature for off-axis tensile and shear test of Sitka spruce (Picea sitchensis Carr.), Katsura (Cercidiphyllurn japonicurn Sieb. and Zucc.), Douglas fir (Pseudotsuga menziesii), Douglas fir laminated veneer and Cupiúba (Goupia glabra) are used for the purpose of this study.

An Experimental Investigation of the Size Effects in Forming Processes of High-Purity Thin Metallic Sheets

Miniaturization of small metallic systems can lead to a softening of the mechanical behavior due to the reduction of scale. Size effects have been considerably studied recently for materials with various crystallographic structures. Under tensile conditions, thin specimen exhibit softer mechanical properties when the number of grains across thickness is lower than a critical number and this modification appears above a critical strain level. In this work, stamping tests were performed on five hundred micrometers in thickness sheets of hexagonal closed-packed cobalt. The results are compared with those obtained for face centered cubic copper and nickel. The influence of thickness over grain size ratio was studied for several proportional loadings linked to forming processes. Complex loadings were applied with 20 mm hemispherical punch and strain paths were checked with a 3D video extensometer. Hill criterion was systematically used to take into account the anisotropy of the samples. Our results revealed that the critical strain level for which the size effects appears is strongly sensitive to the stress triaxiality which, in turn, is closely dependent to the loading path.

Reevaluation and Classification of Duodenal Lesions in B6C3F1 Mice and F344 Rats from 4 Studies of Hexavalent Chromium in Drinking Water

Thirteen-week and 2-year drinking water studies conducted by the National Toxicology Program (NTP) reported that hexavalent chromium (Cr(VI)) induced diffuse epithelial hyperplasia in the duodenum of B6C3F1 mice but not F344 rats. In the 2-year study, Cr(VI) exposure was additionally associated with duodenal adenomas and carcinomas in mice only. Subsequent 13-week Cr(VI) studies conducted by another group demonstrated non-neoplastic duodenal lesions in B6C3F1 mice similar to those of the NTP study as well as mild duodenal hyperplasia in F344 rats. Because intestinal lesions in mice are the basis for proposed safety standards for Cr(VI), and the histopathology data are relevant to the mode of action, consistency (an important Hill criterion for causality) was assessed across the aforementioned studies. Two veterinary pathologists applied uniform diagnostic criteria to the duodenal lesions in rats and mice from the 4 repeated-dose studies. Comparable non-neoplastic intestinal lesions were evident in mice and rats from all 4 studies; however, the incidence and severity of intestinal lesions were greater in mice than rats. These findings demonstrate consistency across studies and species and highlight the importance of standardized nomenclature for intestinal pathology. The differences in the severity of non-neoplastic lesions also likely contribute to the differential tumor response.

Research on Strain Rate-Dependent Tsai-Hill Strength Criterion for Ethylene Propylene Diene Monomer Film

EPDM film is an innovative insulation material used in the Solid Rocket Motor. İt is a kind of unidirectional single layer fiber-reinforced composite plate. To analyze its mechanical behavior uniaxial tests with different loading directions and rates were performed. The test results indicated that the EPDM film is anisotropic and its mechanical properties are obviously rate-dependent. To create a rate-dependent anisotropic strength criterion, two methods were adopted to extend the Tsai-Hill strength criterion; the first was to substitute all the strength components in the Tsai-Hill criterion with the fitted rate-dependent ones, the second was to introduce a special factor named the rate-dependency factor R(ε) into the criterion. The second method is simpler in form and more suitable for an engineering application. The two rate-dependent criteria were examined by comparing the predicted results with the experimental ones, and the results showed good agreement which verified that the strength criteria were able to reveal the anisotropic rate-dependent properties of the EPDM film.