scholarly journals Effects of Defects on the Performance of Hierarchical Honeycomb Metamaterials Realized Through Additive Manufacturing

2016 ◽  
Author(s):  
Kazi Moshiur Rahman ◽  
Todd Letcher ◽  
Zhong Hu
Keyword(s):  
Finite Element ◽  
Cell Walls ◽  
Zero Order ◽  
Second Order ◽  
Cellular Structures ◽  
Plastic Behavior ◽  
First Order ◽  
Honeycomb Structures ◽  
Elastic Plastic ◽  
Large Structures

Cellular metamaterials are of immense interest for many current engineering applications. Tailoring the structural organization of cellular structures leads to new metamaterials with superior properties leading to low weight and very strong/stiff materials. Incorporation of hierarchy to regular cellular structures enhances the properties and introduces novel tailorable metamaterials. For many complex cellular metamaterials, the only realistic manufacturing process is additive manufacturing (AM). The use of AM to manufacture large structures may lead to several types of defects during the manufacturing process, such as missing/broken cell walls, irregular thickness, flawed joints, missing (partial) layers, and irregular elastic plastic behavior due to toolpath. For large structures, it would be beneficial to understand the effect of defects on the overall performance of the structure to determine if the manufacturing defect(s) are significant enough to abort and restart or whether the material can still be used. Honeycomb structures are used for the high strength to weight ratio applications. These metamaterials have been studied and several models have been developed based on idealized cell structures to explain their elastic plastic behavior. However, these models do not capture real-world manufacturing defects resulting from AM. The variation of elastic plastic behavior of regular honeycomb structures with defects has been studied, but the performance of hierarchical honeycomb structures with defects is still unknown. In this study, the effects of missing cell walls are investigated to understand the elastic behavior of hierarchical honeycomb structures through simulations using finite element analysis. Regular (zero order), first order and second order hierarchical honeycombs have been investigated in this study. The first level of hierarchy has been implemented by changing each three edge vertex of a regular hexagonal honeycomb lattice by adding another smaller hexagon. The second level of hierarchy is created by adding another smaller hexagon at each three edge vertex of the hexagons added for the first order hierarchy. For the hierarchical cases, the overall density of the honeycomb is held constant to the parent structure (zero order or regular) by reducing the thickness of the cell wall in the first and second order structures. ANSYS® was used to develop finite element models to analyze the performance of both perfect and defected regular, first order and second order hierarchical honeycombs. Defects were added to the model by randomly removing cell walls. Hierarchical honeycombs demonstrated more sensitivity to missing cell walls than regular honeycombs. On average, the elastic modulus decreased by 45% with 5.5% missing cell walls for regular honeycombs, 60% with 4% missing cell walls for first order hierarchical honeycomb and 95% with 4% missing cell walls for second order hierarchical honeycombs.

In-Plane Stiffness of Additively Manufactured Hierarchical Honeycomb Metamaterials With Defects

2017 ◽  
Vol 140 (1) ◽  
Author(s):  
Kazi Moshiur Rahman ◽  
Zhong Hu ◽  
Todd Letcher
Keyword(s):  
Elastic Modulus ◽  
Manufacturing Process ◽  
Cell Walls ◽  
Second Order ◽  
Plastic Behavior ◽  
Manufacturing Defects ◽  
First Order ◽  
Large Structures ◽  
Overall Performance ◽  
Current Engineering

Cellular metamaterials are of interest for many current engineering applications. The incorporation of hierarchy to cellular metamaterials enhances the properties and introduces novel tailorable metamaterials. For many complex cellular metamaterials, the only realistic manufacturing process is additive manufacturing (AM). The use of AM to manufacture large structures may lead to several types of manufacturing defects, such as imperfect cell walls, irregular thickness, flawed joints, partially missing layers, and irregular elastic–plastic behavior due to toolpath. It is important to understand the effect of defects on the overall performance of the structures to determine if the manufacturing defect(s) are significant enough to abort and restart the manufacturing process or whether the material can still be used in its nonperfect state. In this study, the performance of hierarchical honeycomb metamaterials with defects has been investigated through simulations and experiments, and hierarchical honeycombs were shown to demonstrate more sensitivity to missing cell walls than regular honeycombs. On average, the axial elastic modulus decreased by 45% with 5.5% missing cell walls for regular honeycombs, 60% with 4% missing cell walls for first-order hierarchical honeycomb and 95% with 4% missing cell walls for second-order hierarchical honeycomb. The transverse elastic modulus decreased by about 45% with more than 5.5% missing cell walls for regular honeycomb, about 75% with 4% missing cell walls for first-order and more than 95% with 4% missing cell walls for second-order hierarchical honeycomb.

Effect of Defect on Elastic/Plastic and Creep Behavior of Bone: A Finite Element Study

2007 ◽  
Author(s):  
A. Ajdari ◽  
P. K. Canavan ◽  
H. Nayeb-Hashemi ◽  
G. Warner
Keyword(s):  
Mechanical Properties ◽  
Finite Element ◽  
Trabecular Bone ◽  
Fatigue Loading ◽  
Dimensional Structure ◽  
Plastic Behavior ◽  
Element Analysis ◽  
Elastic Plastic ◽  
Local Bone ◽  
Osteoporotic Vertebral Fractures

Three-dimensional structure of trabecular bone can be modeled by 2D or 3D Voronoi structure. The effect of missing cell walls on the mechanical properties of 2D honeycombs is a first step towards understanding the effect of local bone resorption due to osteoporosis. In patients with osteoporosis, bone mass is lost first by thinning and then by resorption of the trabeculae [1]. Furthermore, creep response is important to analyze in cellular solids when the temperature is high relative to the melting temperature. For trabecular bone, as body temperature (38 °C) is close to the denaturation temperature of collagen (52 °C), trabecular bone creeps [1]. Over the half of the osteoporotic vertebral fractures that occur in the elderly, are the result of the creep and fatigue loading associated with the activities of daily living [2]. The objective of this work is to understand the effect of missing walls and filled cells on elastic-plastic behavior of both regular hexagonal and non-periodic Voronoi structures using finite element analysis. The results show that the missing walls have a significant effect on overall elastic properties of the cellular structure. For both regular hexagonal and Voronoi materials, the yield strength of the structure decreased by more than 60% by introducing 10% missing walls. In contrast, the results indicate that filled cells have much less effect on the mechanical properties of both regular hexagonal and Voronoi materials.

scholarly journals A Dynamic Analysis of the Rotary Cutting System of King Grass Shredder

2020 ◽  
Vol 145 ◽  
pp. 02080
Author(s):  
Zunxiang Li ◽  
Ou Zhongqing ◽  
Jiao jing ◽  
Huang xiaohong ◽  
Du jihua
Keyword(s):  
Finite Element ◽  
Critical Speed ◽  
Great Influence ◽  
Second Order ◽  
Belt Drive ◽  
Finite Element Models ◽  
Rotating Shaft ◽  
First Order ◽  
Rotary Cutting ◽  
Cutting System

With the rotary cutting system of king grass shredder as the research object, this paper established finite element models for rotating shaft, rotating shaft-belt pulley, rotating shaft-rotary cutting part and rotary cutting system and analyzed the influences of belt pulley and rotary cutting part on the dynamic characteristics of rotary cutting system. The results showed that the belt pulley and rotary cutting part had a great influence on the second order critical speed of rotary cutting system, and the rotary cutting part had a greater influence on the critical speed of first order forward precession than the belt pulley. Meanwhile, the critical speed of rotary cutting system that conformed to facts was calculated. There was a big difference between its first order and second order critical speeds, but the critical speed of first order backward precession was lower. Finally, it was found after analysis that the natural frequency of rotary cutting system was lower than the vibration frequency induced by belt drive, so the shredder can run safely.

scholarly journals Maximum principles for parabolic systems coupled in both first-order and zero-order terms

1994 ◽  
Vol 17 (4) ◽  
pp. 813-816
Author(s):  
Chiping Zhou
Keyword(s):  
Parabolic Systems ◽  
Zero Order ◽  
Second Order ◽  
Maximum Principles ◽  
First Order

Some generalized maximum principles are established for linear second-order parabolic systems in which both first-order and zero-order terms are coupled.

A Simplified Analysis Method for Complex Piping Systems in Elastic-Plastic-Creep Range

1985 ◽  
Vol 107 (2) ◽  
pp. 148-156
Author(s):  
O. Watanabe ◽  
H. Ohtsubo
Keyword(s):  
Finite Element ◽  
Present Method ◽  
Constitutive Relations ◽  
Plastic Behavior ◽  
Piping System ◽  
Curved Beams ◽  
Elastic Plastic ◽  
Piping Systems ◽  
Creep Deformations ◽  
Plastic Creep

The present paper describes a simplified finite element method for analysis of behavior of complex piping systems under elevated temperature. Elastic-plastic-creep deformations of a piping system under a combined moment loading can be analyzed by the present method. The system is idealized by straight and curved beams, and derivation of the finite element equation is based on the force method. The unified constitutive relations are used for creep and plastic behavior, where plastic deformation is treated as a limiting case of creep. The numerical results are compared with previous experimental ones, which verifies the validity of the proposed method. Elastic follow-up problem of a piping system of actually complex configuration is also solved by the present method.

Seismic Analysis of Soil Nailed Wall Using Finite Element Method

2012 ◽  
Vol 535-537 ◽  
pp. 2027-2031 ◽  
Author(s):  
Jian Chun Wu ◽  
Rong Shi
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Seismic Analysis ◽  
Retaining Wall ◽  
Plastic Behavior ◽  
Soil Nailing ◽  
Nonlinear Fem ◽  
Elastic Plastic ◽  
Flexible Retaining Wall ◽  
Element Method

Using dynamic elastic-plastic finite element method, on the base of works together and interaction between loess and flexible retaining wall, 3-D nonlinear FEM (ADINA) is used to analyze and discussed the dynamic response of slope protected by soil nailing retaining wall under the EL-Centro and man-made Lanzhou accelerogram. A model that is capable of simulating the nonlinear static and dynamic elastic-plastic behavior of soil is used to model the soil, and a bilinear elastic-plastic model that has hardening behavior is used to model the soil nailing. Friction-element is employed to describe the soil-structure interaction behavior.The results show that the method is safe and credible. The results of the FEM dynamic analysis can be a useful reference for engineers of the design and construction of the soil nailed wall.

Structure Optimization of the Housing Fillet Using SA Combined with FEM

2014 ◽  
Vol 898 ◽  
pp. 217-220
Author(s):  
Jin Hong Ma ◽  
Bin Tao ◽  
Xiao Han Yao
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Simulated Annealing Algorithm ◽  
Structure Optimization ◽  
Optimization Method ◽  
Zero Order ◽  
Optimal Method ◽  
First Order ◽  
Universal Mill ◽  
Annealing Algorithm

The housing fillet of universal mill affects the strengthen and stiffness of mill. It is necessary to optimize the housing fillet. In this paper, the simulated annealing algorithm (SA) combined with finite element method (FEM) , a new kind of structural optimization method is established. MATLAB language is used to compile the program combined the SA with FEM to optimize housing fillet of universal mill. Compared with the zero order and first order optimization method of ANSYS program, the result of this optimal method is better.

scholarly journals Latvian language as a code in different communication channels

2015 ◽  
Vol 3 ◽  
pp. 11
Author(s):  
Linda Bajarune ◽  
Andris Ozols
Keyword(s):  
Computer Program ◽  
Shannon Entropy ◽  
Communication Channels ◽  
Zero Order ◽  
Second Order ◽  
Third Order ◽  
First Order ◽  
Legal Literature

<p class="R-AbstractKeywords">This paper is dedicated to analyze of Latvian language as a code in such literary communication channels like press, poet, prose, legal literature. Calculations for zero-order, first-order, second-order and third-order Shannon entropy have been made and also corresponding values of redundancy and compression coefficients have been determined. All the calculations are done with a self-made computer program. Different communication channels of Latvian language are compared mutually and also Latvian language is compared with English and Russian as codes.</p>

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