Accepted Manuscripts

Benliang Zhu, Rixin Wang, Hai Li and Xianmin Zhang
J. Mech. Des   doi: 10.1115/1.4039975
In level-set-based topology optimization methods, the spatial gradients of the level set field need to be controlled to avoid excessive flatness or steepness at the structural interfaces. One of the most commonly utilized methods is to generalize the traditional Hamilton-Jacobi equation by adding a diffusion term to control the level set function to remain close to a signed distance function near the structural boundaries. This study proposed a new diffusion term and built it into the Hamilton-Jacobi equation. This diffusion term serves two main purposes: (I) maintaining the level set function close to a signed distance function near the structural boundaries, thus avoiding periodic re-initialization, and (II) making the diffusive rate function be a bounded function so that a relatively large time step can be used to speed up the evolution of the level set function. A two-phase optimization algorithm is proposed to ensure the stability of the optimization process. The validity of the proposed method is numerically examined on several benchmark design problems in structural topology optimization.
TOPICS: Diffusion (Physics), Optimization, Topology, Hamilton-Jacobi equations, Design, Optimization algorithms, Stability
Yao Wang, Dongpao Hong, Xiaodong Ma and Hairui Zhang
J. Mech. Des   doi: 10.1115/1.4039919
System reliability assessment is a challenging task when using computationally intensive models. In this work, a radial based centralized Kriging method is proposed for achieving high efficiency and accuracy. The method contains two components: Kriging based system most probable point (MPP) search and radial based centralized sampling. The former searches for the system MPP by progressively updating Kriging models regardless of the nonlinearity of the performance functions. The latter refines the Kriging models with the training points collected from pre-generated samples. It concentrates the sampling in the important high-probability density region. Both components utilize a composite criterion to identify the critical Kriging models for system failure. The final Kriging models are sufficiently accurate only at those sections of the limit states that bound the system failure region. Its efficiency and accuracy are demonstrated via application to three examples.
TOPICS: Reliability, System failures, Probability, Density, Composite materials
Design Innovation Paper  
Mohammad Hussein Kahrobaiyan, Etienne Thalmann, Lennart Rubbert, Ilan Vardi and Simon Henein
J. Mech. Des   doi: 10.1115/1.4039887
Classical mechanical watch plain bearing pivots have frictional losses limiting the quality factor of the hairspring-balance wheel oscillator. Replacement by flexure pivots leads to drastic friction reduction and an order of magnitude increase of the quality factor. However, flexure pivots have drawbacks including gravity sensitivity, nonlinearity and limited stroke. This paper analyses these issues in the case of the cross-spring flexure pivot and presents an improved version addressing them. We first show that the cross-spring pivot cannot be simultaneously linear, insensitive to gravity and have long stroke: the 10 ppm accuracy required for mechanical watches holds independently of the orientation with respect to gravity only when the leaf springs cross at 12.7% of their length. But, in this case the pivot is nonlinear and the stroke is only 31% of the symmetrical (50% crossing) cross-spring pivot’s stroke. The symmetrical pivot is also unsatisfactory as its gravity sensitivity is of order 10^4 ppm. This paper introduces the co-differential concept which we show is gravity insensitive. It is used to construct a long stroke gravity insensitive flexure pivot consisting of a main rigid body, two co-differentials and a torsional beam. We show that this novel pivot achieves linearity or the maximum stroke of symmetrical pivots while retaining gravity insensitivity.
TOPICS: Gravity (Force), Bending (Stress), Springs, Symmetry (Physics), Q-factor, Wheels, Plain bearings, Friction
Technical Brief  
Katja Holtta-Otto, Kevin N. Otto, Chaoyang Song, Jianxi Luo, Timothy Li, Carolyn C. Seepersad and Warren P Seering
J. Mech. Des   doi: 10.1115/1.4039851
Ten years ago it was shown that an innovative mechanical product embodies on average three characteristics of innovation. At the time it was not known if these product were to be successful innovations and if the amount or type of innovation characteristics would be related with success. In this work, we categorized the products from the previous data set into well- and under-adopted products. Due to the significant difference between new ventures and established firms we separated products based on in which type of firm launched them. We show that the innovative products enjoy a success rate of 77% on average. The success is not dependent on the amount or type of innovation characteristics in the set where they all embody on average three characteristics. However, products developed in new ventures embody, on average, one more innovation characteristic and enjoy a success rate of 90%.
TOPICS: Mechanical products, Innovation
Technical Brief  
Zhengwei Hu and Xiaoping Du
J. Mech. Des   doi: 10.1115/1.4039770
Component reliability can be estimated by either statistics-based methods with data or physics-based methods with models. Both types of methods are usually independently applied, making it difficult to estimate the joint probability density of component states, which is a necessity for an accurate system reliability prediction. The objective of this study is to investigate the feasibility of integrating statistics- and physics-based methods for system reliability analysis. The proposed method employs the first-order reliability method directly for a component whose reliability is estimated by a physics-based method. For a component whose reliability is estimated by a statistics-based method, the proposed method applies a supervised learning strategy through Support Vector Machines to infer a linear limit-sate function that reveals the relationship between the component states and basic random variables. With the integration of statistics- and physics-based methods, the limit-state functions of all the components in the system will then be available. As a result, it is possible to predict the system reliability accurately with all the limit-state functions.
TOPICS: Reliability, Physics, Statistics as topic, Density, Event history analysis, Probability, Support vector machines
Ping Du and Erin F. MacDonald
J. Mech. Des   doi: 10.1115/1.4039768
Consumers often use a product's visual design as a mental shortcut to judge its unobservable attributes. Mental associations between visual design and unobservable attributes aid consumers in their judgments, and hypothetically reduce consumers' mental load. This paper describes a study that shows the possibility of quickly creating an association in subjects' minds between a holistic visual cue of a product–its body shape–and the general idea of “environmentally friendly” versus “not environmentally friendly,” a typically unobservable attribute. In this study, products' actual environmental friendliness was not measured. Subjects completed an association-building task, which allowed them to learn predetermined associations between a product's visual cues and its “environmental friendliness” rating, an arbitrarily predetermined rating the authors supplied. The body shape was successfully used as a cue to subliminally communicate to subjects the product's “environmental friendliness.” As a comparison, an individual feature of the product was also used to cue; however, that was unsuccessful. An eye-tracking device was used to identify where subjects were focusing their eyes and for how long. In both the association-building task and a testing task that followed, subjects spent a greater percentage of time looking at the product's cued areas (the body and the selected feature). But during the testing task, subjects spent an even higher percentage of their time looking at the cued areas than they did during the association-building task. This indicates that mental associations, or cues, work to distribute mental load more efficiently.
TOPICS: Design, Shapes, Stress, Testing
John Meluso and Jesse Austin-Breneman
J. Mech. Des   doi: 10.1115/1.4039494
Parameter estimates in large-scale complex engineered systems affect system evolution yet can be difficult and expensive to test. Systems engineering uses analytical methods to reduce uncertainty, but a growing body of work from other disciplines indicates that cognitive heuristics also affect decision-making. Results from interviews with expert aerospace practitioners suggest that engineers bias estimation strategies. Practitioners reaffirmed known system features and posited that engineers may bias estimation methods as a negotiation and resource conservation strategy. Specifically, participants reported that some systems engineers ``game the system'' by biasing requirements to counteract subsystem estimation biases. An agent-based model simulation which recreates these characteristics is presented. Model results suggest that system-level estimate accuracy and uncertainty depend on subsystem behavior and are not significantly affected by systems engineers' ``gaming'' strategy.
TOPICS: Engineers, Systems engineers, Simulation, Systems engineering, Aerospace industry, Analytical methods, Engineering disciplines, Decision making, Uncertainty, Negotiation
Design Innovation Paper  
Leah Gaffney, Paul M. Loschak and Robert D. Howe
J. Mech. Des   doi: 10.1115/1.4039495
A bracing device for stabilizing cardiac catheters inside the heart was developed to provide surgical-level dexterity to minimally invasive catheter-based procedures for cardiac valve disease. The brace was designed to have a folding structure which lies flat along a catheter during navigation through vasculature and then unfolds into a rigid bracing configuration after deployment across the interatrial septum. The brace was designed to be easily deployable, provide bracing support for a transseptal catheter, and also be compliant enough to be delivered to the heart via tortuous vasculature. This aims to improve dexterity in catheter-based mitral valve repair and enable other complex surgical procedures to be done with minimally invasive instruments.
TOPICS: Bracing (Construction), Catheters, Surgery, Valves, Instrumentation, Diseases, Navigation, Maintenance
Steffen Hau, Alexander York, Gianluca Rizzello and Stefan Seelecke
J. Mech. Des   doi: 10.1115/1.4039104
State of the art actuator technologies, e.g., solenoids or pneumatic cylinders, are available in nearly infinite variations to address every specific application. However, for a large number of applications, dielectric elastomers (DE) represent a more energy efficient, lightweight, and low-cost solution with respect to the established technologies mentioned above. In addition to large strain, low power consumption, and high flexibility, DE actuators (DEA) have also highly scalable performance, which allow to adapt them to a large variety of applications. An effective means to scale DE performance is represented by the scaling of material geometry. In fact, a DE membrane can be easily designed in different sizes and shapes. However, in order to perform a successful design, the relation between material geometry and performance has to be properly investigated. In this paper, performance scaling by means of geometry is studied for circular out-of-plane DEAs. Such actuators consist of a silicone elastomer membrane sandwiched between two electrodes (carbon black silicone mixture). DEAs with six different geometries are manufactured, and a model-based strategy is used to find an experimental relationship between geometry and electro-mechanical characteristics. In addition, an effective and computationally simple method for predicting force-displacement characteristics of different geometries, given by a specific material combination (elastomer and electrode), is presented. The proposed method allows to easily adapt DEAs to different applications in terms of stroke and force requirement, while minimizing at the same time both characterization and prototyping effort.
TOPICS: Elastomers, Scaling laws (Mathematical physics), Actuators, Membranes, Geometry, Silicones, Electrodes, Displacement, Energy consumption, Shapes, Design, Pneumatic cylinders, Carbon black pigments, Solenoids
Design Innovation Paper  
Rami Alfattani and Craig Lusk
J. Mech. Des   doi: 10.1115/1.4037621
This paper presents a new Bistable Collapsible Compliant Mechanism (BCCM) that is utilized in a Lamina- Emergent Frustum. The mechanism is based on transforming a polygon spiral into spatial frustum shape using a mechanism composed of compliant links and joints that exhibits bistable behavior. A number of mechanism types (graphs) were considered to implement the shape-morphing spiral, including 4-bar, 6-bar, and 8-bar chains. Our design requirements permitted the selection of a particular 8-bar chain as the basis for the BCCM. Bistable behavior was added to the mechanism by introducing snap-through bistability as the mechanism morphs. Parametric CAD was used to perform the dimensional synthesis. The design was successfully prototyped. We anticipate that the mechanism may be useful in commercial small animal enclosures or as a frame for a solar still.
TOPICS: Compliant mechanisms, Chain, Design, Shapes, Computer-aided design, Solar stills
Amy Suski
J. Mech. Des   doi: 10.1115/1.4025965
TOPICS: Design

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