Alessandro Naddeo

FEM modeling of the reinforcement mechanism of Hydroxyapatite in PLLA scaffolds produced by supercritical drying, for Tissue Engineering applications.

Scaffolds have been produced by supercritical CO2 drying of Poly-L-Lactid Acid (PLLA) gels loaded with micrometric fructose particles used as porogens. These structures show a microporous architecture generated by the voids left in the solid material by porogen leaching, while they maintain the nanostructure of the gel, consisting of a network of nanofilaments. These scaffolds have also been loaded with Hydroxyapatite (HA) nanoparticles, from 10 to 50% w/w with respect to the polymer, to improve the mechanical properties of the PLLA structure. Based on miscroscopic and mechanical considerations, we propose a parametric Finite Element Method (FEM) model of PLLA-HA composites that describes the microporous structure as a close-packing of equal spheres and the nanoscale structure as a space frame of isotropic curved fibers. The effect of HA on the mechanical properties of the scaffolds has been modeled on the basis of SEM images and by taking into consideration the formation of concentric cylinders of HA nanoparticles around PLLA nanofibers. Modeling analysis confirms that mechanical properties of these scaffolds depend on nanofibrous network connections and that bending is the major factor causing deformation of the network. The FEM model also takes into account the formation of HA multi-layer coating on some areas in the nanofiber network and its increase in thickness with HA percentage. The Young modulus tends to a plateau for HA percentages larger than 30% w/w and when the coverage of the nanofibers produced by HA nanoparticles reaches a loaded surface index of 0.14 in the FEM model.

Methodology development of human task simulation as PLM solution related to OCRA ergonomic analysis

In the current demanding global marketplace, ensuring that human fit, form and function are comprehensively addressed, is becoming an increasingly important aspect of design and, in particular, obliges the most important automotive industries to develop more flexible assembly lines and better methods for PLM solution. In the meantime, designers attempt to elaborate product development methodologies that conform health and safety standards while still maximizing the productivity. The aim of this work consists in developing a methodology based on preventive ergonomics and feasibility analyses of assembly tasks, simulating a work cell, in which acts a digital human model (manikin), in order to maximize human safety and performance and analyze manikin interaction in the virtual environment. In ergonomic analyses the OCRA protocol will be used, evaluating different involvement degrees of upper limb segments. The methodology is carried out by ergonomic tool of DELMIA software, using Digital Human Models technology.

Finite elements/Taguchi method based procedure for the identification of the geometrical parameters significantly affecting the biomechanical behavior of a lumbar disc

Abstract The aim of this work is to show a quick and simple procedure able to identify the geometrical parameters of the intervertebral disc that strongly affect the behavior of the FEM model. First, we allocated a selection criterion for the minimum number of geometrical parameters that describe, with a good degree of approximation, a healthy human vertebra. Next, we carried out a sensitivity analysis using the ‘Taguchi orthogonal array’ to arrive at a quick identification of the parameters that strongly affect the behavior of the Fem model.

FEM and BEM Analysis of a Human Mandible with Added Temporomandibular Joints

Mathematical modelling of human mandible and its temporomandibular joints (TMJs) is one of the most important steps for developing a powerful forecasting tool to analyse the stress/strain behaviour of a human masticatory system under occlusal loads. In this work the structural behaviour of a mandible with articular discs, undergoing a unilateral occlusion, is numerically analysed by means of both Finite Element Method (FEM) and Boundary Element Method (BEM). The mandible is considered as completely edentulous and its anisotropic and non-homogeneous bone material behaviour is modelled. The material behaviour of the articular discs was assumed to be either elastic or hyper-elastic. The loads applied to the mandible are related to the active muscle groups during a unilateral occlusion. The results of FEM and BEM analyses are presented mainly in terms of stress distribution on the mandible and on the articular discs. Due to the uncertainty in the determination of the biological parameters, a sensitivity analysis is provided, which demonstrates the impact of the variation of articular disc stiffness and TMJ friction coefficient on the mandible stress peaks and on the occlusal loads (for a given intensity of muscle loads). Moreover a comparison between the effectiveness of the BEM and FEM numerical approaches on this kind of problem is provided.

Dashboard Reachability and Usability Tests: A Cheap and Effective Method for Drivers' Comfort Rating

General comfort may be defined as the “level of well-being” perceived by humans in a working environment. The state-ofthe-art about evaluation of comfort/discomfort shows the need for an objective method to evaluate the “effect in the internal body” and “perceived effects” in main systems of comfort perception. In the early phases of automotive design, the seating and dashboard command can be virtually prototyped, and, using Digital Human Modeling (DHM) software, several kinds of interactions can me modeled to evaluate the ergonomics and comfort of designed solutions. Several studies demonstrated that DHM approaches are favorable in virtual reachability and usability tests as well as in macro-ergonomics evaluations, but they appear insufficient in terms of evaluating comfort. Comfort level is extremely difficult to detect and measure; in fact, it is affected by individual perceptions and always depends on the biomechanical, physiological, and psychological state of the tester during task execution. These parameters cannot be modeled using software and instead have to be tested on physical models.

Manual Assembly Workstation Redesign Based on a New Quantitative Method for Postural Comfort Evaluation

Main purpose of this work is to show how easy and economics an ergonomic/comfort based approach, in re-design a manual assembly workplace, can be; authors, using a new comfort/ergonomic evaluation criterion, analyzed a workstation and identified the critical issues under ergonomic/comfort point of view and finally gave several guidelines to re-design the workplace, implementing minor modification, and improve work-safety, work-quality and productivity. The postural analysis was performed by non-invasive and especially inexpensive methods, based on cameras and video-recorder use and by photogrammetric analysis; DELMIA® DHM software has been used to perform all simulations; comfort analysis was performed by the software developed by researchers of Departments of Industrial Engineering of Salerno: CaMAN®. The test case is an automatic assembly machine that has been modeled and used for virtual postural analysis. Main results of this work can be found in a very good numerical/experimental correlation between acquired/simulated postures and real ones, and on the powerful use of an objective comfort evaluation method, based on biomechanics and posture analysis, for giving to designers the guidelines to re-design a workplace and a work-cycle. This kind of approach seemed to be very powerful in re-designing the work-place and in re-scheduling the work time-sheet because it allowed to improve an ergonomic corrective action with minor costs for company. Obtained results demonstrated the validity of re-design hypotheses through the increase of all comfort indexes and the improvement of workstation/operator productivity.

Comfort-Driven Design of Car Interiors: A Method to Trace Iso-Comfort Surfaces for P ositioning the Dashboard Commands

General comfort can be defined as the measure of the “level of wellbeing” perceived by humans when interacting with a working environment. The state of the art for comfort/discomfort evaluation shows the need for an objective method to evaluate both “effects on the internal body” and “perceived effects” when considering the perception of comfort. Medical studies show that each joint has its own natural resting posture. In this posture, our muscles are completely relaxed or at minimum levels of strain. The bodys geometrical configuration corresponds to the natural resting position of arms/legs/neck etc.

A survey of methods to detect and represent the human symmetry line from 3D scanned human back

This paper proposes a review of the methods to detect and represent the human symmetry line. In the last years, the development of 3D scanners has allowed to replace the traditional techniques (marking based methods) with modern methodologies that, starting from a 3D valid discrete geometric model of the back, perform the posture and vertebral column detection based on a complex processing of the acquired data. The purpose of the paper is a critical discussion of the state of the art in order to highlight the real potentialities and the limitations still present of the most important methodologies proposed for human symmetry line detection.

Fuzzy-logic application in the structural optimisation of a support plate for electrical accumulator in a motor vehicle

Abstract In this paper, we analyse the design of a support plate for the accumulator of an electric motor vehicle. The support is an integral part of motor vehicle chassis. Therefore, geometrical configuration and boundary conditions require careful optimisation research of both function and structural behaviour, since lightness and dimension problems in the presence of dynamic stresses due to external factors have to be considered. Since these factors are complex and not homogeneous, the problem requires multi-criteria analysis. The presence of factors that are not precisely computable calls for fuzzy-logic application to optimisation problems, because fuzzy-logic is non-standard logic, particularly suitable for making choices in structural design. In plate optimisation, in fact, not numerically quantifiable characteristics such as a part’s workability, numerically determinable structural values such as stresses and strains, and analytically calculable properties such as weight come into play. These four parameters become the domain of fuzzy membership functions, by which we will extract membership grade values (co-domain). Design variables (domain) are plate thickness, ashlar’s number on the plate and stiffening ashlar’s depth. In our research, we characterise fuzzy correlation between parameters and required characteristics in order to determine, according to non-standard logics, the best topological configuration which corresponds to the optimisation of individualised characteristics in conformity with design constraints. Results show value improvement in stress and strain in comparison with the not yet optimised plate and small reduction in workability, whereas the mass is almost the same.

Ergonomic-driven redesign of existing work cells: the “Oerlikon Friction System” case

The application of ergonomic principles to the design of processes, workplaces and organizations is not only a way to respond to legal requirements but also an indispensable premise for any company seeking to pursue a business logic. This paper shows a cheap and effective method to perform the ergonomic analysis of worker postures in order to optimize productivity and obtain the highest ergonomic ratings. Evaluations were performed for the 5°, 50° and 95° percentiles according to OCRA and NIOSH methods of biomechanical risk assessment. The results highlighted the need for improvements. A virtual simulation using DELMIA® software and the use of workers’ checklists drew attention to problems causing significant physical stress, as identified by ergonomic tools. An ergonomic/comfort-driven redesign of the work cell was carried out, and CaMAN® software was used to conduct a final comfort-based analysis of the worst workstation in the work cell.