Multi-layered Composites Using Photolithography

The mechanical properties of the parts made using solid freeform fabrication technologies are limited by their resins used. Previous research has shown that the mechanical properties of these parts can be enhanced substantially by using glass and fiber reinforcements. However, all of the published data is for single layered composites, which does not demonstrate its feasibility to manufacture multilayered real objects. In this paper experiments carried out to build multi-layered parts with glass fiber tow as reinforcement in a matrix of photopolymeric resin are described. These specimens are then tested in uniaxial tension and three point bending to determine their improvement in mechanical properties. The experimental data shows that the tensile strength and tensile modulus increased linearly with the volume fraction of the fiber in the composite, thus demonstrating that the trends observed in single layer composites can be also seen in multi-layered composites.Mechanical Engineerin

Adaptive lamina generation for shape dependent process control and/or object decomposition

A method of automatically operating a machine with respect to an object having a desired profile, wherein the machine\u27s operation is controlled based on a model of the object\u27s profile. The method includes generating at least a portion of the model in the form of a plurality of successive layers wherein the cross-section of each layer is defined by the intersection of a pair of parallel planes and a model profile connecting the parallel planes. Each layer\u27s thickness is selected such that the geometrical error between the object\u27s desired profile and the model profile of the layer remains no greater than a preselected geometrical error. More than one layer thickness is selected during the step of generating this portion of the object. The machine can be operated in successive steps with each step based on a separate one of the layers

STR-866: NON LINEAR FINITE ELEMENT MODEL FOR POST-EARTHQUAKE FIRE PERFORMANCE EVALUATION OF STEEL PORTAL FRAMES

Post-earthquake fires (PEF) especially in densely populated urban areas have been catastrophic in recent seismic events. It appears to be an important design load which has not been considered critical by most design standards. Moreover, current performance-based seismic design philosophy permits certain level of damage to a structure based on the assumed design seismic hazard. These damaged structures are extremely vulnerable to post-earthquake fires. Even after the outbreak of fire, the structural integrity of the damaged structure must be intact for sufficient duration enabling the firefighters to evacuate and extinguish the fire in the affected building. The recent performance-based design, necessitates evaluation of the fire resistance level of earthquake damaged building with or without the outbreak of post-earthquake fire. In this study an integrated seismic and thermal analysis model was developed using the sequential thermal–structural analysis scheme using the finite element program, ABAQUS. A simple portal frame was considered to investigate the global behaviour of the frame and determine post-earthquake fire resistance. A 2D transient heat transfer analysis was conducted and the transient nodal temperatures across the structural elements cross sections were stored for subsequent thermal structural analyses. The state of earthquake inflicted damage, corresponding to desired performance level was realized using pushover analysis. The results of the simplified 2D model matched reasonably well with that of 3D finite element model considered for validation study. The developed model is being used for subsequent study to investigate the multi-story moment resisting frames with fire scenarios resulting in asymmetric heating of the frame

Apparatus and method for layered modeling of intended objects represented in STL format and adaptive slicing thereof

A device for automating operation of a stereolithography apparatus uses an STL file as an input and includes a programmable computer, a facet processor that sorts the facets of the STL file according to a predetermined slice axis. The facet processor also groups the sorted facets according to those having common minimum vertex values with respect to the slice axis. The facet processor also subgroups the grouped facet file according to facets having common maximum vertex values with respect to the slice axis. A key characteristic identifier identifies key characteristics of the STL file. A thickness calculator determines the thickness of each layer of the model according to a geometrical error of preselected magnitude. A slicer calculates the intersection of each sliced plane by the calculated thickness. A directional ordering device insures uniformity with the direction of each other contour that defines the intersection. A model generator uses the layer thickness and intersection information to generate a portion of a model. An interface device controls the operation of the machine based on the model that is generated

Asynchronous receivers in narrowband packet radio applications

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1997.Includes bibliographical references.by Amit G. Bagchi.M.Eng

Coupled modeling for investigation of blast induced traumatic brain injury

Modeling of human body biomechanics resulting from blast exposure is very challenging because of the complex geometry and the substantially different materials involved. We have developed anatomy based high-fidelity finite element model (FEM) of the human body and finite volume model (FVM) of air around the human. The FEM model was used to accurately simulate the stress wave propagation in the human body under blast loading. The blast loading was generated by simulating C4 explosions, via a combination of 1-D and 3-D computational fluid dynamics (CFD) formulations. By employing the coupled Eulerian-Lagrangian fluid structure interaction (FSI) approach we obtained the parametric response of the human brain by the blast wave impact. We also developed the methodology to solve the strong interaction between cerebrospinal fluids (CSF) and the surrounding tissue for the closed-head impact. We presented both the arbitrary Lagrangian Eulerian (ALE) method and a new unified approach based on the material point method (MPM) to solve fluid dynamics and solid mechanics simultaneously. The accuracy and efficiency of ALE and MPM solvers for the skull-CSF-brain coupling problem was compared. The presented results suggest that the developed coupled models and techniques could be used to predict human biomechanical responses in blast events, and help design the protection against the blast induced TBI

Benchmarking of Rapid Prototyping Systems - Beginning to Set Standards

Many rapid prototyping (RP) technologies are available today and more are being developed around the world. The absence of benchmarking standards in the RP industry has led manufacturers to use their own standards and make claims about superior performance. The need for testing standards is already felt; standardization will become imperative in the near future. The present work aims to lay the groundwork for the development of standards to measure various performance factors. Issues such as appearance and finish are studied qualitatively; the test part and some findings are presented. Issues such as repeatability, warpage, curl, creep, shrinkage and tensile strength are proposed to be studied quantitatively; test parts designed for studying these are described. Benchmarking standards will help users choose proper systems for their applications and help operators in monitoring machine performance, enabling better control over part building.Mechanical Engineerin

Analysis of Combat Helmet Performance Integrating Blast Loading and Blunt Impact through Simulation

The mild traumatic brain injury (mTBI) is one of the most common injuries to service members in recent conflicts. Combat helmets have been designed and evaluated to perform against ballistic and blunt impact threats, but not blast threats. An optimal design of combat helmet considering blunt, ballistic impacts and blast effects is a key requirement to improve the head protection against mTBI. Combat helmets are usually designed based on costly and time consuming laboratory tests. Computational models can offer insights in understanding the force transmission through the head-helmet system into the brain and underlying mechanism of brain injury, and help the development of effective protective design. We developed a design approach integrating the effect of both blast and blunt threats to a helmet system by utilizing multi-physics computational tools and representative human head and helmet models. The high-fidelity computational models were used to capture the dynamic response of the composite shell, suspension pads, retention straps and head. Multiple helmet system configurations subjected to blast and blunt loadings with a combination of loading magnitude and orientation were considered to quantify their influence on brain biomechanical response. Parametric studies were carried out to assess energy absorption for different suspension geometry and material morphology for different loadings. The resulting brain responses in terms of pressure, stress, strain, and strain rate as well as the head acceleration were used with published injury criteria to characterize the helmet system performance through a single metric for each threat type. Approaches to combine single-threat metrics to allow aggregating performance against multiple threats were discussed

Accelerated boundary integral method for multiphase flow in non-periodic geometries

An accelerated boundary integral method for Stokes flow of a suspension of deformable particles is presented for an arbitrary domain and implemented for the important case of a planar slit geometry. The computational complexity of the algorithm scales as O(N) or $O(N\log N$), where $N$ is proportional to the product of number of particles and the number of elements employed to discretize the particle. This technique is enabled by the use of an alternative boundary integral formulation in which the velocity field is expressed in terms of a single layer integral alone, even in problems with non-matched viscosities. The density of the single layer integral is obtained from a Fredholm integral equation of the second kind involving the double layer integral. Acceleration in this implementation is provided by the use of General Geometry Ewald-like method (GGEM) for computing the velocity and stress fields driven by a set of point forces in the geometry of interest. For the particular case of the slit geometry, a Fourier-Chebyshev spectral discretization of GGEM is developed. Efficient implementations employing the GGEM methodology are presented for the resulting single and the double layer integrals. The implementation is validated with test problems on the velocity of rigid particles and drops between parallel walls in pressure driven flow, the Taylor deformation parameter of capsules in simple shear flow and the particle trajectory in pair collisions of capsules in shear flow. The computational complexity of the algorithm is verified with results from several large scale multiparticle simulations.Comment: Journal of Computational Physics, to appea