Snapping algorithm and heterogeneous bio-tissues modeling for medical surgical simulation and product prototyping

This paper presents a novel technique for modeling soft biological tissues as well as the development of an innovative interface for bio-manufacturing and medical applications. Heterogeneous deformable models may be used to represent the actual internal structures of deformable biological objects, which possess multiple components and non-uniform material properties. Both heterogeneous deformable object modeling and accurate haptic rendering can greatly enhance the realism and fidelity of virtual reality environments. In this paper, a tri-ray node snapping algorithm is proposed to generate a volumetric heterogeneous deformable model from a set of object interface surfaces between different materials. A constrained local static integration method is presented for simulating deformation and accurate force-feedback based on the material properties of a heterogeneous structure. Biological soft tissue modeling is used as an example to demonstrate the proposed techniques. By integrating the heterogeneous deformable model into a virtual environment, users can both observe different materials inside a deformable object as well as interact with it by touching the deformable object using a haptic device. The presented techniques can be used for surgical simulation, bio-product design, bio-manufacturing, and medical applications.     

一种新颖的用于触觉再现的平行菱形链连接模型

针对如何提高虚拟触觉再现的精度与实时性问题,提出了一种新颖的基于物理意义的平行菱形链连接触觉变形模型.该模型中各个链结构单元中菱形的长度等比例变化,因而计算量小;改变链结构单元中菱形的长度和夹角就可方便对不同的柔性体进行建模,系统中各个链结构单元的相对位移的叠加对外等效为物体表面的变形,与之相连的弹簧弹性力的合力等效为物体表面的接触力.利用手控器对柔性体的接触变形和实时虚拟触觉反馈进行了仿真.实验表明所提出的方法适用于柔性体的触觉反馈计算,能够满足精细作业对虚拟现实系统的要求.     

Haptic modeling for a virtual coordinate measuring machine

Introducing a haptic device into coordinate measuring machine (CMM) inspection path planning leads to the proposal of a novel CMM off-line inspection path planning environment, a haptic virtual coordinate measuring machine (HVCMM), which makes use of the haptic modeling technique for CMM off-line programming. The HVCMM is an accurate model of a real CMM, which simulates a CMM's operation and its measurement process in a virtual environment with haptic perception. In this paper, a simple and effective mechanics model is implemented for the proposed HVCMM. The HVCMM enables CMM off-line programming to take place exactly as if an operator were in front of a real CMM and moving a real CMM probe. Even more, operators can feel the collision between the CMM and a part. Since there is a force feedback when the probe reaches the surface of the part, besides showing the contact in the HVCMM environment, it is much easier to generate a collision-free probe path than using other off-line inspection planning methods. The HVCMM not only facilitates inspection path planning, but also speeds it up because the operator does not need to slow the probe down when it is approaching an object. Combined visual and force feedback is the best indicator for selecting measurement points.     

Fatigue crack growth simulation in heterogeneous material using s-version FEM

A fully automatic fatigue crack growth simulation system is developed using the s-version Finite Element Method (s-FEM). This system is extended to fractures in heterogeneous materials. In a heterogeneous material, the crack tip stress field has a mixed-mode condition, and the crack growth path is affected by inhomogeneous materials and mixed-mode conditions. Stress intensity factors (SIFs) in the mixed-mode condition are evaluated using the virtual crack closure method (VCCM). The criteria for the crack growth amount and crack growth path are based on these SIFs, and the growing crack configurations are obtained. At first, the basic problem is solved, and the results are compared with some results available in the literature. It is shown that this system gives an adequate accurate estimation of the SIFs. Then, two-dimensional fatigue crack growth problems are simulated using this system. The first example is a plate with an interface between hard and soft materials. The cracks tend to grow in soft materials through the interface. A second example is a plate with distributed hard inclusions. The crack takes a zig-zag path by propagating around the hard inclusions. In each case, the crack growth path changes in a complicated manner. Changes of the SIFs values are also shown and discussed.     

Latest Developments in Modeling and Characterization of Joining Metal Based Hybrid Materials

Advanced materials consist of several materials systems that exhibit complementary properties for multi‐purpose applications. Joining of dissimilar materials is a critical and challenging advanced manufacturing technique to develop novel hybrid materials with properties fully transferred. The “bonding strength” of a joint is crucial for its integrity and performance. The bonding strength is affected by a range of parameters that can be better understood, controlled, and optimized via both experimental and analytical approaches. In this paper, the authors review the theoretical and experimental studies of the interface inside several metal based composites. The scope includes interface bonding's critical parameters, characterization techniques of joining processes, potential applications, and their future perspectives. The review is significant to develop advanced manufacturing techniques for heterogeneous materials and to design innovative heterogeneous systems for various medical, electrical, electronics, industrial, and other daily life applications that involve the broad range of “joining” processes.

     

软物质力学:行为特性、理论模型和测试方法

软物质已成为物理学、化学、材料、力学和生命科学重要的前沿研究课题,在技术和生产上有广阔的应用前景,是国际上普遍重视的多学科交叉研究领域,更是通向研究生命体系的桥梁。软物质力学是力学的一个新兴方向,其研究对推动多学科的交集协同发展有着极其重要的作用。然而,软物质组成复杂,常是多相集合体,且往往涉及与硬物质的界面相互作用,其运动和变化规律与一般流体和固体迥异。软物质中结构单元之间的作用力弱,在一般流体和固体中作用较小的力,如表、界面作用力、范德华力等,可能在软物质中起到主导作用,传统的流体/固体理论已无法全面刻画软物质所呈现的许多独特现象。软物质的本构关系比较复杂,涉及到流变、大变形、熵等新概念。目前,除了软物质物理、化学、生物等相关研究以外,研究者们开始从力学的角度对软物质的行为特性及其理论分析模型与测试方法进行深入探索,在生物力学、界面和接触力学、胶体力学、实验力学等领域取得了丰硕的成果。近几年来,学者们对生物组织、细胞和生物大分子、水凝胶、形状记忆聚合物、活性软材料、柔性电子器件、颗粒、液晶等多种软物质体系进行了力学分析、模拟及实验,探索了软物质微结构形成的物理机制和动力学引起的新生长规律。也有学者将软物质的不稳定性和自组装行为用于开发低成本、高性能的新材料和新设备。还有许多学者考虑学科交叉,从新的角度研究软物质材料,将连续介质力学中的本构关系、计算技术和建模方法引入到软物质模拟计算中,实现对软物质的自组装行为及表面不稳定性的理论分析,并将综合的力学测试方法和技术带入到软物质力学实验中,实现对软物质复杂力学响应的小尺度性能测试。本文论述了软物质材料的力学行为及特性:包括复杂力学响应、自组织行为和表面不稳定性及其相关研究进展;重点讨论了软物质在生物力学、界面和接触力学、胶体力学和实验力学等力学领域的研究发展;对软物质力学的发展前景做了展望,提出了值得进一步研究的方向,以期推动国内软物质力学学科的发展。     

Shear bond of composites-to-brick applied with highly deformable,in relation to resin epoxy,interface materials

The paper presents comparison of a work of stiff and flexible bonds fastening composite strengthening to masonry. In the first approach (traditional), barely deformable interface material made of stiff epoxy resin is used as shear bonds of composites-to-brick. In the second one (innovative), highly deformable interface material made of flexible polymer is used as repair shear bonds of composites-to-brick. Behavior of both materials was compared using single-lap shear tests made on four kinds of fiber fabrics (glass, carbon, basalt and steel) applied to clay brick units. The results indicated that highly deformable interface materials allow increasing load capacity, because deformable adhesive layers reduce shear stress concentrations in bond, redistributing stress more evenly along the whole lap joint. Usefulness of the theory which allows calculating the bond shear stress–slip characteristic was also discussed in accordance to the highly deformable interface materials.     

Direct numerical simulation of saturated deformable porous media using parallel hybrid Lattice–Boltzmann and finite element method

Numerical techniques for modeling saturated deformable porous media have mainly been based on mixture theory or homogenization techniques. However, these techniques rely on phenomenological relationships for the constitutive equations along with assumptions of homogeneous and isotopic material properties to obtain closure. Direct numerical simulations of the multiphasic problem for flow in deformable porous media avoid such assumptions and thus can provide significantly accurate understanding of the physics involved. They serve as a tool to investigate the constitutive relationships in complex geometries. They also allow the validation of the existing mixture theory models and determine their limitations. In this work, a parallel hybrid method using Lattice Boltzmann Method (LBM) for fluid phase and Finite Element Method (FEM) for solid phase is used for direct numerical simulation of saturated deformable porous media. The method provides a number of unique features including scalability on distributed computing necessary for such a problem. The method has been validated for modeling fluid–structure interactions in complex geometries against a number of experimental and analytical solutions. Further some challenging problems has been chosen to show the capability of the method. Copyright © 2010 John Wiley & Sons, Ltd.     

Error Estimation of Nanoindentation Mechanical Properties Near a Dissimilar Interface via Finite Element Analysis and Analytical Solution Methods

Nanoindentation methods are well suited for probing the mechanical properties of a heterogeneous surface, since the probe size and contact volumes are small and localized. However, the nanoindentation method may introduce errors in the computed mechanical properties when indenting near the interface between two materials having significantly different mechanical properties. Here we examine the case where a soft material is loaded in close proximity to an interface of higher modulus, such as the case when indenting bone near a metallic implant. Results are derived from both an approximate analytical quarter-space solution and a finite element model, and used to estimate the error in indentation-determined elastic modulus as a function of the distance from the apex of contact to the dissimilar interface, for both Berkovich and spherical indenter geometries. Sample data reveal the potential errors in mechanical property determination that can occur when indenting near an interface having higher stiffness, or when characterizing strongly heterogeneous materials. The results suggest that caution should be used when interpreting results in the near-interfacial region.     

多尺度材料模型研究及应用

在分别介绍宏观,介观,微观,原子和电子尺度材料模型研究的基础上,论述了多尺度材料模型（MMM）这一新兴的跨学科的前沿研究领域产生的前提,概念主其在材料科学,特别是在宏观形变及新断裂过程研究中的重要作用,综合分析了多种跨尺度关联方法的原理,技术方案及其应用,并探讨了当前多尺度研究的热点及进一步发展的方向。     

Stretchable and Soft Electronics using Liquid Metals

The use of liquid metals based on gallium for soft and stretchable electronics is discussed. This emerging class of electronics is motivated, in part, by the new opportunities that arise from devices that have mechanical properties similar to those encountered in the human experience, such as skin, tissue, textiles, and clothing. These types of electronics (e.g., wearable or implantable electronics, sensors for soft robotics, e‐skin) must operate during deformation. Liquid metals are compelling materials for these applications because, in principle, they are infinitely deformable while retaining metallic conductivity. Liquid metals have been used for stretchable wires and interconnects, reconfigurable antennas, soft sensors, self‐healing circuits, and conformal electrodes. In contrast to Hg, liquid metals based on gallium have low toxicity and essentially no vapor pressure and are therefore considered safe to handle. Whereas most liquids bead up to minimize surface energy, the presence of a surface oxide on these metals makes it possible to pattern them into useful shapes using a variety of techniques, including fluidic injection and 3D printing. In addition to forming excellent conductors, these metals can be used actively to form memory devices, sensors, and diodes that are completely built from soft materials. The properties of these materials, their applications within soft and stretchable electronics, and future opportunities and challenges are considered.     

Freeform modelling using sweep differential equation with haptic interface

This paper presents the development of a virtual sculpting system and addresses the issues of interactive freeform solid modelling with haptic interface. A virtual reality (VR) approach is taken to make the developed system more intuitive and interactive. The virtual sculpting method is based on the metaphor of carving a primitive or imported solid model into a 3D freeform object. The geometric modelling is based on the sweep differential equation method to compute the boundary of the tool swept volume. The ray-casting method is used to perform Boolean operations to simulate the sculpting process. A new method of surface reconstruction from dexel data is presented. The PHANToM™ manipulator is used to provide the position and orientation data of the sculpting tool and also to provide haptic sensation to the user hand during the sculpting. An accuracy analysis is performed to determine the limitations on the sculpted geometric details.     

Liquid Crystalline Elastomer for Separate or Collective Sensing and Actuation Functions

A porous liquid crystalline elastomer actuator filled with an ionic liquid (PLCE-IL) is shown to exhibit the functions of two classes of materials: electrically responsive, deformable materials for sensing and soft active materials for stimuli-triggered actuation. On one hand, upon the order–disorder phase transition of aligned mesogens, PLCE-IL behaves like a typical actuator capable of reversible shape change and can be used to assemble light-fuelled soft robot. On the other hand, at temperatures below the phase transition, PLCE-IL is an elastomer that can sustain and sense large deformations of various modes as well as environmental condition changes by reporting the corresponding electrical resistance variation. The two distinguished functions can also be used collectively with PLCE-IL integrated in one device. This intelligent feature is demonstrated with an artificial arm. When the arm is manually powered to fold and unfold, the PLCE-IL strip serves as a deformation sensor; while when the manual power is not available, the role of the PLCE-IL strip is switched to an actuator that enables light-driven folding and unfolding of the arm. This study shows that electrically responsive LCEs are a potential materials platform that offers possibilities for merging deformable electronic and actuation applications.     

Extreme Toughening of Soft Materials with Liquid Metal

Soft and tough materials are critical for engineering applications in medical devices, stretchable and wearable electronics, and soft robotics. Toughness in synthetic materials is mostly accomplished by increasing energy dissipation near the crack tip with various energy dissipation techniques. However, bio‐materials exhibit extreme toughness by combining multi‐scale energy dissipation with the ability to deflect and blunt an advancing crack tip. Here, we demonstrate a synthetic materials architecture that also exhibits multi‐modal toughening, whereby embedding a suspension of micron sized and highly deformable liquid metal (LM) droplets inside a soft elastomer, the fracture energy dramatically increases by up to 50x (from 250 ± 50 J m^‐2 to 11,900 ± 2600 J m^‐2) over an unfilled polymer. For some LM‐embedded elastomer (LMEE) compositions, the toughness is measured to be 33,500 ± 4300 J m^‐2, which far exceeds the highest value previously reported for a soft elastic material. This extreme toughening is achieved by (i) increasing energy dissipation, (ii) adaptive crack movement, and (iii) effective elimination of the crack tip. Such properties arise from the deformability of the LM inclusions during loading, providing a new mechanism to not only prevent crack initiation, but also resist the propagation of existing tears for ultra tough, soft materials.     

Freeform modelling using sweep differential equation with haptic interface

This paper presents the development of a virtual sculpting system and addresses the issues of interactive freeform solid modelling with haptic interface. A virtual reality (VR) approach is taken to make the developed system more intuitive and interactive. The virtual sculpting method is based on the metaphor of carving a primitive or imported solid model into a 3D freeform object. The geometric modelling is based on the sweep differential equation method to compute the boundary of the tool swept volume. The ray-casting method is used to perform Boolean operations to simulate the sculpting process. A new method of surface reconstruction from dexel data is presented. The PHANToM? manipulator is used to provide the position and orientation data of the sculpting tool and also to provide haptic sensation to the user hand during the sculpting. An accuracy analysis is performed to determine the limitations on the sculpted geometric details.     

Virtual prototyping and manufacturing planning by using tri-dexel models and haptic force feedback

This paper presents a new method of using the tri-dexel volumetric models and a haptics force feedback for virtual prototyping and manufacturing planning. In the proposed method, the initial polyhedral surface model is converted to a tri-dexel volumetric model by using a depth-peeling dexelization algorithm. In the virtual prototyping process, the tri-dexel volumetric model is updated by the swept volume of a moving cutter via a haptic force feedback interface device. A collision detection algorithm is proposed for the virtual sculpting and the pencil-cut planning with real-time haptic force feedback to the users. Tool paths are generated for machining the virtual sculpted parts via the simulation and verification on a virtual CNC machine tool before they are actually machined. Computer implementation and practical examples are also presented in this paper. The proposed method enables the haptic-aided virtual prototyping and manufacturing planning of complex surface parts.     

Numerical modelling of fracture of particulate composites using SPH method

Simplicity of mesh generation and robustness against mesh entanglement during large deformations are key attractive features of particle based methods. These features can be exploited in number of engineering problems where traditional techniques suffer due to aforementioned limitations. Numerical modelling of particulate composites is one of such ideal engineering applications where particle based methods can be effectively used due to their simplicity and robustness. Complicated geometrical configurations of particulate composites obtained from techniques such as scanning electron microscopy (SEM) can be easily converted to particle based mesh without loosing much information. This enables more accurate analysis of the chosen composite materials. Therefore, a smooth particle hydrodynamics (SPH) based numerical technique is developed here to investigate the mechanical properties and evolution of debonding process in particulate composites. To perform the numerical study, a Lagrangian corrected SPH (CSPH) method is presented together with an appropriate numerical model for treating material interface discontinuity within the particulate composites. The material interface discontinuity is enforced using an innovative method which combines penalty formulation with a bilinear interface cohesive model for SPH method. The proposed SPH methodology is used in a number of numerical examples involving composite materials and related interface problems. The effect of penalty value on the interface model and of the smoothing length of the SPH method are also analysed during these simulations. The results illustrate the effectiveness, robustness and potential of the developed methodology. It is concluded that the proposed numerical techniques can be easily and effectively applied to simulate multi-phase composites with various interface conditions and, can provide useful information regarding the inherent mechanism of damage evolution and fracture of particulate or fibre reinforced composites.     

Virtual prototyping and manufacturing planning by using tri-dexel models and haptic force feedback

This paper presents a new method of using the tri-dexel volumetric models and a haptics force feedback for virtual prototyping and manufacturing planning. In the proposed method, the initial polyhedral surface model is converted to a tri-dexel volumetric model by using a depth-peeling dexelization algorithm. In the virtual prototyping process, the tri-dexel volumetric model is updated by the swept volume of a moving cutter via a haptic force feedback interface device. A collision detection algorithm is proposed for the virtual sculpting and the pencil-cut planning with real-time haptic force feedback to the users. Tool paths are generated for machining the virtual sculpted parts via the simulation and verification on a virtual CNC machine tool before they are actually machined. Computer implementation and practical examples are also presented in this paper. The proposed method enables the haptic-aided virtual prototyping and manufacturing planning of complex surface parts.     

Electrical characterization of semiconductor materials and devices—review

Semiconductor materials and devices continue to occupy a pre-eminent technological position because of their importance in building integrated electronic systems for wide ranging applications from computers, cell-phones, personal digital assistants, digital cameras and electronic entertainment systems, to electronic instrumentation for medical diagnostics and environmental monitoring. A key ingredient of this technological dominance has been the rapid advances in the quality and processing of materials—semiconductors, conductors and insulators—thus providing the complementary metal-oxide-semiconductor device technology with its important characteristics of negligible standby power dissipation, good input–output isolation, surface potential control and reliable operation. However, in assessing the material quality and device reliability, it is important to have non-destructive, accurate and easy-to-use electrical characterization techniques available, so that important parameters such as carrier doping density, type and mobility of carriers, interface quality, oxide trap density, semiconductor bulk defect density, contact and other parasitic resistances and oxide electrical integrity can be rapidly determined. This article describes some of the more widely used and popular techniques that are used to determine these important parameters. The techniques presented in this paper range in complexity and requirements for test structures. It ranges from the simple current–voltage measurements, to the more sophisticated low-frequency noise and deep-level transient spectroscopy techniques.     

Strategies and challenges for the mechanical modeling of biological and bio-inspired materials

The mechanical modeling of biological materials has received much attention due to diverse applications in medicine and engineering. Biological materials are often structurally hierarchical and may possess highly desirable structure–property relations that serve as templates for bio-inspired materials. This paper reviews the strategies that have been employed for the mechanical modeling of biological and bio-inspired materials, and outline the outstanding challenges. The review focuses on models based on the following approaches: single-scale versus multi-scale, microstructural versus phenomenological, and continuum versus discrete. Challenges in scale-bridging, integrated microstructural representation at all hierarchies and accurate constitutive modeling are discussed. In particular, inverse modeling and cross-property correlations are viewed as future challenges for the modeling of bio-inspired materials.