Obtaining and Characterizing Alginate/k-Carrageenan Hydrogel Cross-Linked with Adipic Dihydrazide

The aim of this paper is obtaining and characterizing hydrogels based on different ratios of oxidized alginate (oA) and k-carrageenan (C), chemically cross-linked with adipic dihydrazide (adh). The alginate (A) was first oxidized with sodium metaperiodate in order to transform it into the dialdehyde derivative, a more reactive compound than alginate. A known procedure for oxidation of alginate with sodium metaperiodate in ethanol-water in order to improve alginate reactivity by transforming the hydroxyl end-groups into dialdehyde was used, preceded by a partially cleavage of the alginate chains. In the second stage, the mixture of dialdehydic derivative of oxidized alginate, k-carrageenan and glycerol subjected to reaction with adipic dihydrazide leads to a Semi-Interpenetrated Network covalently cross-linked alginate/k-carrageenan hydrogel (oACadh), based on the dihydrazone compound which is responsible for the chemical cross-linking. Pure alginate, k-carrageenan, oxidized alginate, adipic dihydrazide and the cross-linked hydrogel were characterized by: FTIR, XRD, and SEM

Mechanical behavior of beams with variable stiffness obtained by 3D printing

Additive manufacturing or 3D printing gained a widespread popularity in recent years due to the ability of the method to manufacture components with high geometrical complexity. The most cost-effective process to manufacture plastic parts using 3D printing is the fused deposition modeling (FDM) method. Process parameters as the infill rates but also the printed pattern of different layers and their orientation have a significant influence on the mechanical properties of specimens fabricated by FDM. Controlling the process parameters is possible to generate materials with variable mechanical proprieties. The paper presents the analysis of a beam with constant cross-section but variable stiffness. Variable stiffness is achieved by changes in different cross-sections of the beam of the infill rates of the printing process. The mechanical behavior consisting of force-displacements curves is analyzed by three-point bending tests of variable stiffness samples and comparison with similar beams having constant infill rate. The results consist of E-modulus variation, maximum force and deflection curve. Analytical calculations and finite element analyses are employed to predict the mechanical behavior of the specimens printed with variable infill rate. The obtained results proved the concept of equal stress-beam with constant cross-section obtained by 3D printing process parameters variation

Numerical and Experimental Evaluation of a Battery Cell under Impact Load

Impact damage is one of the most critical scenarios for the lithium-ion battery pack of an electrical vehicle, as it involves mechanical abusive loads with serious consequences on electrical and thermal stability. The development of a numerical model for an explicit dynamic simulation of a Li-ion battery pack under impact implies a significant computational effort if detailed models of a single battery cell are employed. The present paper presents a homogenized finite element model of a battery cell, validated by experimental tests of individual materials and an impact test of an entire cell. The macro model is composed of shell elements representing outside casing and elements with a homogenized and isotropic material for the jelly roll. The displacements and deformed shape of the numerical model of the battery cell were compared with those measured on real test specimens; full-field optical scanning was employed to reconstruct the 3D shape of the deformed battery. The overall deformation of the simulation and experimental results are comparable with a deviation of the maximum intrusion of 14.8% for impact direction and 19.5% for the perpendicular direction considering the cumulative effects of simplifying hypotheses of the numerical model and experimental side effects. The results are a starting point for future analyses of a battery pack and its protection systems under impact. The model presented in this paper, considering the low computing power needed for calculation and acceptable mesh size for crash, should be able to be used in bigger resources consuming crash simulation models. In this way, the cells’ deformation and behavior can be tracked more easily for safety management and diagnosis of the crashworthiness of the packs or car batteries

Numerical and Experimental Evaluation of a Battery Cell under Impact Load

Impact damage is one of the most critical scenarios for the lithium-ion battery pack of an electrical vehicle, as it involves mechanical abusive loads with serious consequences on electrical and thermal stability. The development of a numerical model for an explicit dynamic simulation of a Li-ion battery pack under impact implies a significant computational effort if detailed models of a single battery cell are employed. The present paper presents a homogenized finite element model of a battery cell, validated by experimental tests of individual materials and an impact test of an entire cell. The macro model is composed of shell elements representing outside casing and elements with a homogenized and isotropic material for the jelly roll. The displacements and deformed shape of the numerical model of the battery cell were compared with those measured on real test specimens; full-field optical scanning was employed to reconstruct the 3D shape of the deformed battery. The overall deformation of the simulation and experimental results are comparable with a deviation of the maximum intrusion of 14.8% for impact direction and 19.5% for the perpendicular direction considering the cumulative effects of simplifying hypotheses of the numerical model and experimental side effects. The results are a starting point for future analyses of a battery pack and its protection systems under impact. The model presented in this paper, considering the low computing power needed for calculation and acceptable mesh size for crash, should be able to be used in bigger resources consuming crash simulation models. In this way, the cells’ deformation and behavior can be tracked more easily for safety management and diagnosis of the crashworthiness of the packs or car batteries

Numerical Investigation of the Infill Rate upon Mechanical Proprieties of 3D-Printed Materials

The paper proposes a novel method of numerical simulation of the fused deposition molding 3Dprinted parts. The single filaments are modeled by a script using the G-code of the 3D printer. Based on experimental evaluation of the cross-sectional geometry of a printed tensile specimen, the connection between the filaments is determined and the flattening effect of the filaments can be counted. Finite element (FE) simulations considering different element lengths were validated by experimental tests. The methodology allows, on one hand, numerical estimation of the true cross-sectional area of a specimen and correction of the experimental stress-strain curves and, on the other hand, accurate determination of the E-modulus of a printed tensile specimen with different deposition densities (20%, 40%, 60%, 80% and 100% infill rate). If the right method to connect the single filaments is established and validated for a 3D printer, the mechanical properties of the 3D specimens can be predicted without physical tensile test, only using FE method, which will allow the designers to print out the parts with variable infill rate and tunable stiffness only after the FE result are suitable for their needs, saving considerably materials and time

The Topological Optimization and the Design for Additive Manufacturing of a Steering Knuckle for Formula SAE Electric Vehicle

Formula Student represents the main motorsport activity for future professionals during their academic preparation. There is intensive migration from the prototypes with an internal combustion engine to electrical vehicles. The challenge of electric vehicles is the weight of the batteries which has to be compensated. The Topological Optimization process represents a method of removing volume and mass of the component (elements of mesh) with the aid of the discretization allowed by the finite element method (FEM) until a mass or stress constraint is attained. The results come in a complex shape, the material being kept only in the stressstrain directions. The manufacturing process is usually as complex, being employed high complexity technologies such as Selective Laser Melting (SLM). Improved strength-to-weight ratio materials are to be considered to obtain the most performant design of a specific component. The present paper presents the topological optimization process of the steering knuckle for the Formula Student electric vehicle of ART-TU Team of Technical University of Cluj-Napoca. It means that the part is simulated and optimized through Ansys Static Structural and there is done post-processing of the component along with Data Validation. The conclusions consist of the viability of the Topological Optimization process when designing complex components for performance automotive

Generation of Computational 3D Models of Human Bones Based on STL Data and CAD Software Packages

This paper presents three methods of converting complex 3D models of STL type into solid models. For converting the STL models, specific approximation functions from CATIA and Creo Parametric software were used as well as 3D solid modeling methods that used sketches drawn for sections of the specific analyzed model. This conversion is required to get a solid 3D model that can be used for finite element analysis and to be processed using Boolean functions in specific CAD programs. This paper also presents a study of the effectiveness of FEA in respect to the time required for the analysis of each converted model. The analyzed STL files contain data obtained by computer tomography and are the 3D models of the human orthopedic system: the left zygomatic bone and upper part of the right femur. The presented conversion methods can be used by design engineers both in medical applications (where the complexity of forms is well known) for the design of implants and for industrial applications for reverse engineering

Carbon epoxy front hood for an electrical city vehicle

In the last decade fiber-reinforced polymer (FRP) had a very impressive development. Due to its physical and mechanical properties, this material is used in many high-end domains such as: aerospace, aviation, automotive, medical, engineering or building constructions. In the last period FRP are being intensely used in the automotive industry especially for the chassis manufacturing and other vehicle structural components. In this paper, the authors present the model of a carbon epoxy front hood of a two-passenger electrical car which is specially designed in urban area and which makes use of advanced FRP manufacturing

Bending and compression tests for PA 2200 parts obtained using Selective Laser Sintering method

Craniofacial bone defects that produce morphological and functional disabilities can bring alteration of the quality of patient’s life. For this reason, the collaboration between the field of medicine with engineering, lead to the manufacture of custom implants from biocompatible materials. In the last years it was shown that Additive Manufacturing methods are very helpful to achieve customized medical implants. All the customized implants made of biocompatible materials have to be tested for mechanical properties, in order to have the optimal characteristics for the area were will be used. This paper presents the results for bending and compression tests for a biocompatible material, PA 2200. The samples were achieved using Selective Laser Sintering method and were obtained with different laser power, starting with 4 W. Maximum load, maximum stress, specific deformation and Young's modulus were analysed. The study showed that different mechanical properties can be obtained, depending on the laser power used. At bending tests, increasing values were obtained for the investigated parameters along with laser power increasing, but at compression tests a different trend was observed