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Journal of Mechanical Design

The ASME Journal of Mechanical Design (JMD) serves the broad design community as a venue for scholarly, archival research in all aspects of the design activity.
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  • Featured Article: ASSESSING QUALITY OF USER-SUBMITTED NEED STATEMENTS FROM LARGE-SCALE NEEDFINDING: EFFECTS OF EXPERTISE AND GROUP SIZE

    Cory R. Schaffhausen and Timothy M. Kowalewski
    J. Mech. Des 137(12), 121102 (2015); doi: 10.1115/1.4031655
    ​Collecting data on user needs can result in overwhelming amounts of data, especially if user groups are large and diverse. Additional analysis is necessary to prioritize a small subset of needs for further consideration. This study presents a simplified quality metric and online interface appropriate to initially screen and prioritize lists exceeding 500 statements for a single topic or product area. Over 20,000 ratings for 1697 need statements across three common product areas were collected in 6 days.  A series of analyses tested whether particular characteristics of users and groups affect the number of high-quality needs that can be generated.  The evaluated characteristics were user group size, needs submitted per person, and expertise and experience levels of users.  The results provided important quantitative evidence of fundamental relationships between the quantity and quality of need statements. Increased quantities of high-quality need statements resulted both due to increasing user group size and due to increasing counts per person using novel content-rich methods to help users articulate needs. However, a user’s topic-specific expertise (self-rated) and experience level (self-rated hours per week) were not significantly associated with increasing need quality.
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    For the Full Paper please see ASME's Digital Collection.
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  • Featured Article: TOWARD A UNIFIED DESIGN APPROACH FOR BOTH COMPLIANT MECHANISMS AND RIGID-BODY MECHANISMS: MODULE OPTIMIZATION


    J. Mech. Des 137(12), 122301; doi: 10.1115/1.4031294
    Rigid-body mechanisms (RBMs) and compliant mechanisms (CMs) are traditionally treated in significantly different ways. In this paper, we present an approach to the synthesis of both RBMs and CMs. In this approach, RBMs and CMs are generalized into mechanisms that consist of five basic modules, including Compliant Link (CL), Rigid Link (RL), Pin Joint (PJ), Compliant Joint (CJ), and Rigid Joint (RJ). The link modules and joint modules are modeled with beam and hinge elements, respectively, in a geometrically nonlinear finite element solver, and subsequently a discrete beam-hinge ground structure model is established. Based on this discrete beam-hinge model, a procedure that follows topology optimization is developed, called module optimization. Particularly, in the module optimization approach, the states (both presence or absence and sizes) of joints and links are all design variables, and one may obtain a RBM, a partially CM, or a fully CM for a given mechanical task. The proposed approach has thus successfully addressed the challenge in the type and dimensional synthesis of RBMs and CMs. Three design examples of the path generator are discussed to demonstrate the effectiveness of the proposed approach.
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    For the Full Article please visit ASME's Digital Collection.
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  • Featured Article: LEVEL SET TOPOLOGY OPTIMIZATION OF PRINTED ACTIVE COMPOSITES

    Multi-material polymer printers allow the placement of different materials within a composite. The individual material phases can be spatially arranged and shaped in an almost arbitrary fashion. Utilizing the shape memory behavior of at least one of the material phases, active composites can be 3D printed such that they deform from an initially flat plate into a curved structure. To navigate this vast design space, systematically and efficiently explorer design options, and find an optimum layout of the composite this paper presents a novel design optimization approach. The optimization approach combines a level set method for describing the material layout and a generalized formulation of the extended finite element method (XFEM) for predicting the response of the printed active composite (PAC). This combination of methods yields optimization results that can be directly printed without the need for additional post-processing steps. The proposed optimization method is studied with examples where the target shapes correspond to a plate-bending type deformation and to a localized deformation. The optimized designs are 3D printed and the XFEM predictions are compared against the experimental measurements. The design studies demonstrate the ability of the proposed optimization method to yield a crisp and highly resolved description of the optimized material layout that can be realized by 3D printing.
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  • Featured Article: An Investigation of Key Design for Additive Manufacturing Constraints in Multi-Material 3D Printing

    Nicholas Meisel
    School of Engineering Design, Technology, and Professional Programs (SEDTAPP)
    The Pennsylvania State University
    213J Hammond Building, University Park, PA, 16802, U.S.A.
    nam20@psu.edu
    ASME Member
     
    Christopher Williams
    Design, Research, and Education for Additive Manufacturing Systems Laboratory,
    Virginia Tech
    413D Goodwin Hall, 635 Prices Fork Road, Blacksburg, VA, 24061, U.S.A.
    cbwill@vt.edu
    ASME Member
    The PolyJet material jetting additive manufacturing (AM) process is uniquely qualified to create complex, multi-material structures.  However, key manufacturing constraints need to be explored and understood in order to guide designers in their use of the PolyJet process including 1) minimum manufacturable feature size, 2) removal of support material, 3) survivability of small features during cleaning, and 4) the self-supporting angle in the absence of support material.  In this study, the authors used a series of experiments to identify statistically significant geometric and process parameters and how they impact part manufacturability.  Support material removal was found to be limited by the cross-sectional area of small channels in the part; a minimum cross-sectional area approximately equal to the diameter of the cleaning water jet spray results in the highest percentage of support material removed from small channels (Figure 1).  The process’s minimum resolvable feature size was shown to rely on surface finish and feature shape, as well as the interactions between surface finish and orientation, surface finish and feature direction, and orientation and feature direction.  If a designer can account for the ideal configuration of these variables, then it is possible to manufacture features that are half the size of a more general “worst-case” scenario.  Feature survivability during the cleaning process was tied to cross-sectional area (for rigid features) and feature connectivity (for flexible features), with flexible features requiring significantly larger feature diameters to survive when fixed at both ends.  Finally, the self-supporting angle in the absence of support material was driven by the orientation of the surface with respect to the roller in the print head assembly, with y-dominated specimens offering better self-supporting angles.  Experimental design studies such as these are crucial to provide designers with the knowledge to ensure that their proposed designs are manufacturable with the PolyJet process, whether designed manually or by an automated method, such as topology optimization.
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    Figure 1. Mean support material removed from channels of various areas
    For the Full Article please visit ASME's Digital Collection.
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