Duane W. Storti

3D-printed mechanochromic materials.

We describe the preparation and characterization of photo- and mechanochromic 3D-printed structures using a commercial fused filament fabrication printer. Three spiropyran-containing poly(ε-caprolactone) (PCL) polymers were each filamentized and used to print single- and multicomponent tensile testing specimens that would be difficult, if not impossible, to prepare using traditional manufacturing techniques. It was determined that the filament production and printing process did not degrade the spiropyran units or polymer chains and that the mechanical properties of the specimens prepared with the custom filament were in good agreement with those from commercial PCL filament. In addition to printing photochromic and dual photo- and mechanochromic PCL materials, we also prepare PCL containing a spiropyran unit that is selectively activated by mechanical impetus. Multicomponent specimens containing two different responsive spiropyrans enabled selective activation of different regions within the specimen depending on the stimulus applied to the material. By taking advantage of the unique capabilities of 3D printing, we also demonstrate rapid modification of a prototype force sensor that enables the assessment of peak load by simple visual assessment of mechanochromism.

Skeleton-based modeling operations on solids

The skeleton is a lower-dimensional geometric abstraction that is useful for performing a number of important geometric operations on solid models. In this paper we develop skeleton-based algorithms that demonstrat,e the utility of the skeleton in addressing: (1) 1 evel-of-detail control, the generation of hierarchical representations that preserve overall shape but blur local boundary features; (2) hexahedral mesh generation, the decomposit,ion of a 3D shape into a collection of block elements suitable for finite element analysis; (3) shape interpolation and morphing, the generation of an “int>ermediate” shape from two given 3D shapes and the generation of a sequence of shapes that smoothly transform one shape into another; and (4) shape synthesis, the generation of an optimal shape from specifications of functional performance requirements and constraints. Besides our goal of providing novel solutions to these problems of significant, practical importance, we seek to illustrate the general usefulness of the skeleton as an intermediate geometric descrig tion that should be more widely implemented in commercial CAD systems.

An accelerated triangulation method for computing the skeletons of free-form solid models

Abstract Shape skeletons are powerful geometric abstractions that provide useful intermediate representations for a number of geometric operations on solid models including feature recognition, shape decomposition, finite element mesh generation, and shape design. As a result there has been significant interest in the development of effective methods for skeleton generation of general free-form solids. In this paper we describe a method that combines Delaunay triangulation with local numerical optimization schemes for the generation of accurate skeletons of 3D implicit solid models. The proposed method accelerates the slow convergence of Voronoi diagrams to the skeleton, which, without optimization, would require impraelically large sample point sets and resulting meshes to attain acceptable accuracy. The Delaunay triangulation forms the basis for generating the topological structure of the skeleton. The optimization step of the process generates the geometry of the skeleton patches by moving the vertices of Delaunay tetrahedra and relocating their centres to form maximally inscribed spheres. The computational advantage of the optimization scheme is that it involves the solution of one small optimization problem per tetrahedron and its complexity is therefore only linear (O(n)) in the number of points used for the skeleton approximation. We demonstrate the effectiveness of the method on a number of representative solid models.

Implicit reconstruction of solids from cloud point sets

Chek T. Lirnl George M. Turkiyyah2 hark A. G’ante# Duane W. storti~ University of Washington Seattle, WA 98195 {ctlim@u, george@ce,ganter@u, storti@u}.Washington.edu This paper describes a new technique that combines numerical optimization methods with triangulation methods for generating mathematical representations of solids from 3D point data. The solid representation obtained takes the form of an algebraic function whose level surface closely approximates the surface described by the data, The algebraic function is obtained via Implicit Solid Modeling, a constructive scheme for approximating Boolean volume set operations on implicitly defined primitive volumes, and is comprised of a blended union of spherical primitives. The parameters of the algebraic function are the spatial locations and radii of the spheres as well as the parameters that describe the blending of these primitives, Fitting an implicit solid model to a data set is formulated as a sequence of non-linear optimization problems of an increasing number of variables. The cost function we employ in these optimizations is a weighted combination of discrepancies in location (distance from points to boundary of reconstructed object), discrepancies in surface normals, and desired curvature characteristics of the reconstructed solid. Since a set of trivariate data points without any connectivity information is ambiguous, an infinite number of solids, in principle, can be constructed to fit them. Different characteristics of the solid can be specified through the cost function to create the most desirable interpretation of the data. The starting point of the optimization—corresponding to the starting configuration of the primitives—is determined by performing a 3D Delaunay triangulation on the data set, and is based on the locations and sizes of the resulting tetrahedral. The effectiveness of the algorithm is demonstrated through the reconstruction of several sample data sets, including a molar and a femur. Tradeoffs between accuracy and compactness of the representations are also examined. 1Department of Mechanical Engineering, FU-10 ‘Department of Civil Engineering, FX-10. Permission to copy without fee all or part of this material is granted provided that the copies are not made or distributed for direct commercial advantage, the ACM copyright notice and the title of the publication and its date appear, and notice is given that copying is by permission of the Association of Computing Machinery.To copy otherwise, or to republish, requires a fee andlor specific permission. Solid Modeling ’95, Salt Lake City, Utah USA

The guide to glass 3D printing: developments, methods, diagnostics and results

Purpose – This purpose of this paper is to provide an overview of the steps and processes behind successfully adapting novel materials, namely virgin glass and recycled glass, to three‐dimensional printing (3DP).Design/methodology/approach – The transition from 3DP ceramic systems to glass systems will be examined in detail, including the necessary modifications to binder systems and printing parameters. The authors present preliminary engineering data on shrinkage, porosity, and density as functions of peak firing temperature, and provide a brief introduction to the complexities faced in realizing an adequate and repeatable firing method for 3D printed glass.Findings – Shrinkage behavior for the 3D printed recycled glass showed significant anisotropy, especially beyond peak firing temperatures of 730°C. The average shrinkage ratios for the slow‐ and fast‐axes to the Z‐axis were 1:1.37 and 1:2.74, respectively. These extreme differences can be attributed to the layer‐by‐layer production method and binder ...

Skeleton-based three-dimensional geometric morphing

Abstract In this paper, we describe a method for generating geometric morphs between general 3D solid models. The method is based on the Euclidean skeleton and is capable of generating morphs between shapes that possess different feature sets and different topology. The essential concept that enables the morphing method is utilization of the trimmed skeleton of the symmetric difference as an intermediate shape. The intermediate shape is a valid solid model whose boundary does not self-intersect and is everywhere equidistant from the boundaries of the source shapes. We apply the skeleton-based intermediate shape generation procedure recursively to produce a sequence of shapes, referred to as a morph history, that gradually transform between the initial and target shapes. The method is sufficiently robust to handle significant changes in geometry and topology, such as the creation and annihilation of protrusions, indentations, internal holes and handles, and produces intuitive morph histories. The skeleton also establishes a correspondence between points on the boundaries of the source and target objects. Interpolation between corresponding points is performed to enable fast generation of a morph history consisting of a sequence of valid solid models. For source and target models that are sufficiently close, this interpolative morphing scheme generates results comparable to those obtained by the recursive skeletonization procedure, but with improved computational efficiency. The boundary point correspondence generated by the skeleton enables morphing with surface attributes (e.g., color, texture, surface roughness, and transparency). The skeleton-based procedure also allows for morphing between open curves or surfaces. A modification of the basic procedure allows the user to control the morph by specifying corresponding feature sets on the initial and final objects. Examples are presented to demonstrate the capabilities of the methods described.

Dynamics of Two Strongly Coupled Relaxation Oscillators

This paper concerns the dynamics of a pair of identical, linearly coupled van der Pol relaxation oscillators. We study the stability of the in-phase and out-of-phase modes of vibration. The stability of both modes is shown to be governed by the behavior of a linear Variational equation with periodic coefficients. Approximate analytical solutions are obtained by the method of matched asymptotic expansions. These analytical results are supplemented by numerical integrations based on Floquet theory.It is shown that previous work based on the sinusoidal (nonrelaxation) limit fails to predict a significant region of instability for both modes.

Subdivision-based multilevel methods for large scale engineering simulation of thin shells

This paper presents a multilevel algorithm to accelerate the numerical solution of thin shell finite element problems de-scribed by subdivision surfaces. Subdivision surfaces have become a widely used geometric representation for general curved three dimensional boundary models and thin shells as they provide a compact and robust framework for mod-eling 3D geometry. More recently, the shape functions used in the subdivision surfaces framework have been proposed as candidates for use as finite element basis functions in the analysis and simulation of the mechanical deformation of thin shell structures. When coupled with standard solvers, however, such simulations do not scale well. Run time costs associated with high-resolution simulations (105 degrees of freedom or more) become prohibitive. The main contribution of the paper is to show that the subdivision framework can be used for accelerating such sim-ulations. Specifically the subdivision matrix is used as the intergrid information transfer operator in a multilevel pre-conditioner. The method described in the paper allows the practical simulation or a broad range of problems. Included examples show that the run time of the algorithm presented scales nearly linearly in time with problem size.

A skeletal-based solid editor

This paper explores the concept of using skeletons as the basis for constructing a solid-editing system. Skeletal data (i.e., the skeleton and the associated maximal sphere radii) offers a valid solid representation scheme, and we examine the capability of the skeletal representation to support shape editing operations. In addition to general discussion of the capabilities of skeletalbased methods, we also present concrete examples of editing operations reahzed in a recent implementation of a skeletonbased solid editor. The im lemented skeletal-based editor imports polyhedral solids or po yhedral approximations of solids) by I, p computing their s eletal data. The editor then displays the skeletal data and provides a simple interface for editing both the skeleton and the sphere radii. The edited skeleton is then “refleshed”, based on the edited skeletal data, to reconstruct the edited solid. The reconstructed solid is represented as the halfspace associated with an implicit tinction, and polygonization methods can be applied to produce output that, like the input, is polyhedral. Editing operations illustrated correspond to stretching, bending, rounding, and uniform or non-uniform thickening of the solid. Discussions of the key enabling technologies including skeletonization, and polygonization are also presented. refleshing,

Development Process for Custom Three-Dimensional Printing (3DP) Material Systems

The development of a new material system for three-dimensional printing (3DP) can be difficult without experience in the field, since the flexibility of the 3DP process implies a large number of material and processing parameters. This paper presents a detailed explanation of the steps involved in developing specific implementations of 3DP, along with tools and insight for each step. This material system development procedure should provide a clear understanding of the 3DP process steps and development decisions to help the user take advantage of the considerable flexibility of 3DP and expedite a new system development. The paper concludes with a demonstration of how the guidance provided is applied in the development of fully dense ceramic dental copings; a research problem uniquely suited to the flexibility of 3DP.