Antonio Lanzotti

The impact of process parameters on mechanical properties of parts fabricated in PLA with an open-source 3-D printer

Purpose – This study aims to quantify the ultimate tensile strength and the nominal strain at break (ɛf) of printed parts made from polylactic acid (PLA) with a Replicating Rapid prototyper (Rep-Rap) 3D printer, by varying three important process parameters: layer thickness, infill orientation and the number of shell perimeters. Little information is currently available about mechanical properties of parts printed using open-source, low-cost 3D printers. Design/methodology/approach – A computer-aided design model of a tensile test specimen was created, conforming to the ASTM:D638. Experiments were designed, based on a central composite design. A set of 60 specimens, obtained from combinations of selected parameters, was printed on a Rep-Rap Prusa I3 in PLA. Testing was performed using a JJ Instruments – T5002-type tensile testing machine and the load was measured using a load cell of 1,100 N. Findings – This study investigated the main impact of each process parameter on mechanical properties and the effe...

Technical Section: Concept design for quality in virtual environment

The early identification of the optimal concept is a critical task of the design process in order to increase the chances of satisfying customers. The challenging aspect of the approach proposed in this work relies in the quality evaluation of virtual prototypes of new industrial products (i.e. concept designs) by adopting a statistical procedure previously applied to service industries. Following this approach, the optimal concept design is defined at the end of a process consisting of five phases: identification of the quality elements of the concept design, classification of the quality elements, generation and quality evaluation of product concepts and, finally, definition of the optimal concept. Currently, virtual reality (VR) environment offers the opportunity to evaluate the characteristics of different virtual prototypes by involving experts and/or customers, overcoming the need for several physical prototypes. On the other side, the dynamics of simulation and the stereoscopic visualization in VR environment provides a more realistic and impressive interaction with virtual prototypes than in CAD environment. The proposed methodology is fully exploited through two case studies: the choice of the optimal design for a traditional Neapolitan coffee maker, addressed by the Italian designer Riccardo Dalisi, and for a subassembly of a new minicar.

A virtual reality approach for usability assessment: case study on a wheelchair-mounted robot manipulator

The aim of the paper is to address an innovative methodology for assessing the usability of a product. This methodology is particularly suitable for designing products that provide their main functions through their control interfaces. In particular, this case study relates to the usability assessment of two control devices for a wheelchair-mounted robot manipulator to assist physically disabled people. The study focuses on defining a synthetic usability index on the basis of two currently used methods: the multi criteria decision analysis and the Saaty’s analytic hierarchy process. Several virtual reality (VR)-based experiments have been conducted, set up in accordance with a cross-array experimental plan, that adequately caters for both control and noise factors. Quantitative measures and subjective user evaluations have been collected to maximize the effectiveness, the efficiency and the satisfaction perceived by users while using the product. Compared to the literature on the subject, the proposed approach provides both more flexibility in defining quantitative indexes and more adequate results, even when involving only a small sample of users in the participatory design session. The use of VR technologies for the collection of the experimental data has been essential in terms of safety, costs and repeatability of the tests, as well as of the robustness with respect to noise factors.

Mechanical behavior of bulk direct composite versus block composite and lithium disilicate indirect Class II restorations by CAD-FEM modeling

OBJECTIVES To study the influence of resin based and lithium disilicate materials on the stress and strain distributions in adhesive class II mesio-occlusal-distal (MOD) restorations using numerical finite element analysis (FEA). To investigate the materials combinations in the restored teeth during mastication and their ability to relieve stresses. METHODS One 3D model of a sound lower molar and three 3D class II MOD cavity models with 95° cavity-margin-angle shapes were modelled. Different material combinations were simulated: model A, with a 10μm thick resin bonding layer and a resin composite bulk filling material; model B, with a 70μm resin cement with an indirect CAD-CAM resin composite inlay; model C, with a 70μm thick resin cement with an indirect lithium disilicate machinable inlay. To simulate polymerization shrinkage effects in the adhesive layers and bulk fill composite, the thermal expansion approach was used. Shell elements were employed for representing the adhesive layers. 3D solid CTETRA elements with four grid points were employed for modelling the food bolus and tooth. Slide-type contact elements were used between the tooth surface and food. A vertical occlusal load of 600 N was applied, and nodal displacements on the bottom cutting surfaces were constrained in all directions. All the materials were assumed to be isotropic and elastic and a static linear analysis was performed. RESULTS Displacements were different in models A, B and C. Polymerization shrinkage hardly affected model A and mastication only partially affected mechanical behavior. Shrinkage stress peaks were mainly located marginally along the enamel-restoration interface at occlusal and mesio-distal sites. However, at the internal dentinal walls, stress distributions were critical with the highest maximum stresses concentrated in the proximal boxes. In models B and C, shrinkage stress was only produced by the 70μm thick resin layer, but the magnitudes depended on the Youngs modulus (E) of the inlay materials. Model B mastication behavior (with E=20GPa) was similar to the sound tooth stress relief pattern. Model B internally showed differences from the sound tooth model but reduced maximum stresses than model A and partially than model C. Model C (with E=70GPa) behaved similarly to model B with well redistributed stresses at the occlusal margins and the lateral sides with higher stress concentrations in the proximal boxes. Models B and C showed a more favorable performance than model A with elastic biomechanics similar to the sound tooth model. SIGNIFICANCE Bulk filling resin composite with 1% linear polymerization shrinkage negatively affected the mechanical behavior of class II MOD restored teeth. Class II MOD direct resin composite showed greater potential for damage because of higher internal and marginal stress evolution during resin polymerization shrinkage. With a large class II MOD cavity an indirect composite or a lithium disilicate inlay restoration may provide a mechanical response close to that of a sound tooth.

The effects of cavity-margin-angles and bolus stiffness on the mechanical behavior of indirect resin composite class II restorations

OBJECTIVE To study the influence of the different class II mesio-occlusal-distal (MOD) cavity shape on the stress and strain distributions in adhesive indirect restorations, using numerical finite element analysis (FEA). To investigate the relationship between restored teeth failure and stiffness of food, three values of Youngs modulus were used for the food. METHODS A 3D model of a sound lower molar and three class II MOD cavities with different shape were created. Slide-type contact elements were used between tooth surface and food. An adhesive resin-based cement, modeled with fixed-type contact elements, and a single restorative filling materials were considered. To simulate polymerization shrinkage effect, which is basically restricted to the thin composite cement layer, shell elements were employed and the thermal expansion approach was used. A vertical occlusal load of 600N was applied, while assigning fixed zero-displacements on the cutting surfaces below the crevices. All the materials were assumed to be isotropic and elastic. A static linear analysis was carried out. RESULTS In the lingual cusp, the displacements increased as the values of the stiffness food increased. In the restored teeth, the stress near the restoration-tooth interface was strongly dependent on the MOD cavity shape. The stress peaks were mainly located along the enamel-dentin interface at the lingual side; wedge-shaped MOD cavity with a low angle, in combination with the lowest food stiffness provided the best results. SIGNIFICANCE A more complex load application on the occlusal surfaces was introduced. Food stiffness slightly affected the stress distribution of the restored and sound teeth. Teeth with adhesive class II MOD indirect resin composite restorations were potentially more susceptible to damage if the class II MOD cavity-margin-angle was higher than 95°. Restored teeth with a higher cavity-margin-angle led to considerable stress concentration in the lingual cusp along the enamel-dentin interface. These models were more susceptible to fracture in the lingual cusps when compared to the buccal ones.

Improving comfort of shoe sole through experiments based on CAD-FEM modeling

It was reported that next to style, comfort is the second key aspect in purchasing footwear. One of the most important components of footwear is the shoe sole, whose design is based on many factors such as foot shape/size, perceived comfort and materials. The present paper focuses on the parametric analysis of a shoe sole to improve the perceived comfort. The sensitivity of geometric and material design factors on comfort degree was investigated by combining real experimental tests and CAD-FEM simulations. The correlation between perceived comfort and physical responses, such as plantar pressures, was estimated by conducting real tests. Four different conditions were analyzed: subjects wearing three commercially available shoes and in a barefoot condition. For each condition, subjects expressed their perceived comfort score. By adopting plantar sensors, the plantar pressures were also monitored. Once given such a correlation, a parametric FEM model of the footwear was developed. In order to better simulate contact at the plantar surface, a detailed FEM model of the foot was also generated from CT scan images. Lastly, a fractional factorial design array was applied to study the sensitivity of different sets of design factors on comfort degree. The findings of this research showed that the sole thickness and its material highly influence perceived comfort. In particular, softer materials and thicker soles contribute to increasing the degree of comfort.

Mechanical behavior of endodontically restored canine teeth: Effects of ferrule, post material and shape

OBJECTIVE To assess the effect of a ferrule design with specific post material-shape combinations on the mechanical behavior of post-restored canine teeth. METHODS Micro-CT scan images of an intact canine were used to create a 3-D tessellated CAD model, from which the shapes of dentin, pulp and enamel were obtained and geometric models of post-endodontically restored teeth were created. Two types of 15mm post were evaluated: a quartz fiber post with conical-tapered shape, and a carbon (C) fiber post with conical-cylindrical shape. The abutment was created around the coronal portion of the posts and 0.1mm cement was added between prepared crown and abutment. Cement was also added between the post and root canal and a 0.25mm periodontal ligament was modeled around the root. Four models were analysed by Finite Element (FE) Analysis: with/without a ferrule for both types of post material and shape. A load of 50N was applied at 45° to the longitudinal axis of the tooth, acting on the palatal surface of the crown. The maximum normal stress criterion was adopted as a measure of potential damage. RESULTS Models without a ferrule showed greater stresses (16.3MPa) than those for models with a ferrule (9.2MPa). With a ferrule, stress was uniformly distributed along the abutment and the root, with no critical stress concentration. In all models, the highest stresses were in the palatal wall of the root. Models with the C-fiber post had higher stress than models with the quartz fiber posts. The most uniform stress distribution was with the combination of ferrule and quartz fiber post. SIGNIFICANCE The FE analysis confirmed a beneficial ferrule effect with the combination of ferrule and quartz fiber post, with tapered shape, affording no critical stress concentrations within the restored system.

A Top-Down Approach for Virtual Redesign and Ergonomic Optimization of an Agricultural Tractor’s Driver Cab

Nowadays, economical, technical and ergonomic factors have a great importance on the design of the agricultural tractors. The paper illustrates the use and the management of heterogeneous product information (manual measurements and drafts, 2D drawings, technical documentation, photos), advanced CAD modeling tools and digital human models, for the redesign and the ergonomic optimization of an agricultural tractor’s driver cab. The project development has been organized using a top–down approach in a collaborative environment. At first, a manual measurement with gauges allowed to realize a technical draft of the whole agricultural tractor and of each component part of the driver cab. Then a main skeleton has been created in Catia V5 environment in order to specify all the datum elements necessary to model each sub-assembly of the tractor. Cabin, platform, engine, tires, seat, dashboard and controls have been organized separately and modeled considering the details related to the manual measurements and to the technical standards. Once obtained the 3D CAD model of the tractor, an opportune questionnaire was prepared and a test campaign was carried out with real operators in order to define the more critical control devices within the driver cab, as regards to usability and ergonomic issues. An “Ergonomics’ Evaluation Index” (EEI) was defined taking into account the posture angles of the operator and the Rapid Upper Limb Assessment analysis tool available in the “Ergonomics Design & Analysis” module of Catia V5 based on the use of a digital human model. The index was validated comparing the results of tests carried out using virtual manikins of different percentiles performing a specific driving task, with the results of tests carried out by real operators, of the same percentiles, performing the same driving task. Critical values of the EEI obtained during some driving tasks in virtual environment, suggested to modify the shape and the position of some control devices in order to optimize the ergonomics of the driver cab. The adoption of the top-down modeling based approach allowed each change on a singular component part to be automatically propagated on the whole assembly, making easy the changes on the virtual prototype.Copyright

Flatness, circularity and cylindricity errors in 3D printed models associated to size and position on the working plane

The purpose of this paper is to assess the main effects on the geometric errors in terms of flatness, circularity and cylindricity based on the size of the printed benchmarks and according to the position of the working plane of the 3D printer. Three benchmark models of different sizes, with a parallelepiped and cylinder shape placed in five different positions on the working plane are considered. The sizes of models are chosen from the Renard series R40. Benchmark models are fabricated in ABS (Acrylonitrile Butadiene Styrene) using Zortrax M200 3D printer. A sample of five parts for each geometric category, as defined from the R40 geometric series of numbers, is printed close to each corner of the plate, and in the plate center position. Absolute Digimatic Height Gauge 0-450mm with an accuracy of ±0.03mm by Mitutoyo is used to perform all measurements: flatness on box faces, and circularity/cylindricity on cylinders. Results show that the best performances, in terms of form accuracy, are reached in the area center printable while they decrease with the sample size. Being quality a critical factor for a successful industrial application of the AM processes, the results discussed in this paper can provide the AM community with additional scientific data useful to understand how to improve the quality of parts which may be obtained through new generations of 3D printer.

A Digital Pattern Approach to the Design of an Automotive Power Window by means of Object-Oriented Modelling

The paper deals with a digital pattern (DP) approach to the design of an automotive power window, using object-oriented modelling. Therefore, the paper faces the designing of a mechatronic system by using an integrated approach to product development. Then, Dymola/Modelica environment is used as a tool of a decision support system that makes possible the DP approach. The paper briefly sum up the results of simulations related to a power window system characterized by a double bowden sliding mechanism. Finally, the paper highlights the parameters that could be easily integrated in a graphical user interface, aimed to reduce both the development time of new power window system and to increase the accuracy of design activities.