Kishore Pochiraju

Long-Term Durability of Polymeric Matrix Composites

Long-Term Durability of Polymeric Matrix Composites presents a comprehensive knowledge-set of matrix, fiber and interphase behavior under long-term aging conditions, theoretical modeling and experimental methods.This bookcovers long-term constituent behavior, predictive methodologies, experimental validation and design practice. Readers will also find a discussion of various applications, including aging air craft structures, aging civil infrastructure, in addition to engines and high temperature applications.

Color point cloud registration with 4D ICP algorithm

This paper presents methodologies to accelerate the registration of 3D point cloud segments by using hue data from the associated imagery. The proposed variant of the Iterative Closest Point (ICP) algorithm combines both normalized point range data and weighted hue value calculated from RGB data of an image registered 3D point cloud. A k-d tree based nearest neighbor search is used to associated common points in {x, y, z, hue} 4D space. The unknown rigid translation and rotation matrix required for registration is iteratively solved using Singular Value Decomposition (SVD) method. A mobile robot mounted scanner was used to generate color point cloud segments over a large area. The 4D ICP registration has been compared with typical 3D ICP and numerical results on the generated map segments shows that the 4D method resolves ambiguity in registration and converges faster than the 3D ICP

A Computer-Aided Optimization Approach for the Design of Injection Mold Cooling Systems

A methodology is presented for the design of optimal cooling systems for injection mold tooling which models the mold cooling as a nonlinear constrained optimization problem. The design constraints and objective function are evaluated using Finite Element Analysis (FEA). The objective function for the constrained optimization problem is stated as minimization of both a function related to part average temperature and temperature gradients throughout the polymeric part. The goal of this minimization problem is to achieve reduction of undesired defects as sink marks, differential shrinkage, thermal residual stress built-up, and part warpage primarily due to non-uniform temperature distribution in the part. The cooling channel size, locations, and coolant flow rate are chosen as the design variables. The constrained optimal design problem is solved using Powells conjugate direction method using penalty function. The cooling cycle time and temperature gradients are evaluated using transient heat conduction simulation. A matrix-free algorithm of the Galerkin Finite Element Method (FEM) with the Jacobi Conjugate Gradient (JCG) scheme is utilized to perform the cooling simulation. The optimal design methodology is illustrated using a case study.

Heterogeneous Thermo-oxidative Behavior of Multidirectional Laminated Composites

This article examines the through-the-thickness heterogeneity observed in oxidation profiles of composite laminates. The effect of ply angle on oxygen diffusivity and the influence of ply stacking sequence on oxidation behavior of isothermally aged multidirectional composites are discussed by correlating experimental observations and a three-dimensional oxidation model. Experimental observations of oxidation growth are made using dark-field optical microscopy, while damage initiation and growth is detected using fluorescence imaging with dye impregnation. Oxidation growth in laminated systems is simulated using a diffusion-reaction-conversion model developed earlier for resin oxidation along with homogenization techniques. Several stacking sequences of carbon fiber-reinforced polyimide composites are studied. The effects of the orthotropy in the diffusivity tensors of each ply and the influence of neighboring ply on oxidation growth are clearly illustrated. The simulation results presented in this article are valid till the onset of damage, beyond which coupling effects between oxidation growth and damage evolution have to be addressed.

Structure-modulus relationships for injection-molded long fiber-reinforced polyphthalamides

Abstract The structural information needed for modulus evaluation of long fiber-reinforced composites includes the fiber volume fraction, the modulus and the Poissons ratio of the constituents, the fiber orientation and the fiber length distribution. In this work, the fiber orientation distribution is expressed in terms of three parameters which may vary with spatial location on the part: the average orientation angle on the surface, the average orientation angle on the mid-plane and the thickness of shell-core layers. With the independent evaluation of the fiber length distribution, composite models are used to evaluate mechanical property distribution such as modulus and Poissons ratio as a function of spatial location on the part. The approach used in this work combines the Halpin-Tsai equations and a stiffness modeling scheme which follows a combination of iso-stress and iso-strain averaging techniques to determine the anisotropic material behavior of these composites. The predictions are compared with experimental data from injection-molded plaques fabricated at different processing conditions. Modulus variation with location is measured by fabricating dog-bone tensile samples from the plaques at four in-flow and four cross-flow positions. Modulus variability is shown to be high with location and the model captures this non-uniformity over the whole range of tested samples.

Point cloud segmentation with LIDAR reflection intensity behavior

Light Detection and Ranging (LIDAR) scans are increasingly being used for 3D map construction and reverse engineering. The utility and benefit of the processed data maybe enhanced if the objects and geometry of the area scanned can be segmented and labeled. In this paper, we present techniques to model the intensity of the laser reflection return from a point during LIDAR scanning to determine diffuse and specular reflection properties of the scanned surface. Using several illumination models, the reflection properties of the surface are characterized by Lambertian diffuse reflection model and Blinn-Phong, Gaussian and Beckmann specular models. Experimental set up with eight different surfaces with varied textures and glossiness enabled measurement of algorithm performance. Examples of point cloud segmentation with the presented approach are presented.

Remotely Operated and Autonomous Mapping System (ROAMS)

The development of a relatively low cost mobile 3D mapping robot prototype named ROAMS (Remotely Operated and Autonomous Mappings Systems) which enables rapid generation of high resolution 3D maps of indoor/outdoor environments is presented. The Robotic system generates 3D maps using a video registered Lidar scanning system integrated with a multiple degree of freedom actuator. This vehicle is also used as a test platform for conducting studies and real-time experiments on autonomous operations. Environmental awareness sensors in combination with a long range wireless communications system is used to enable remote operation and monitoring of ROAMS. Techniques for improving the resolution and point distribution of Lidar data through the use of video images and actuator speed control are also investigated and presented.

Oxidation-induced damage evolution in a unidirectional polymer matrix composite

Long-term degradation and failure in high-temperature polymer matrix composites are driven by chemical changes due to oxidation reactions and damage evolution. In this paper, we present a methodology for simulating oxidation-induced damage in a unidirectional composite. This approach explicitly models the time-dependent growth of oxidation layers and the evolution of discrete cracking in a homogenized representation of the composite. Long-term isothermal aging is simulated with high-resolution tracking of morphological changes and damage evolution. An element-free Galerkin method is used to simulate the oxidation layer growth, and the extended finite element method is used for computing the stress fields and predicting damage. The developed model captures both oxidation and damage growth in the unidirectional lamina through long periods of oxidative aging. The model predictions correlate well with the experimental results for a carbon/polyimide composite system.

Three‐Dimensional Simulation of Moisture Diffusion in Polymer Composite Materials

Abstract This article presents a three‐dimensional Galerkin finite element methodology (GFEM) for simulating Fickian diffusion with temperature‐dependent diffusion coefficients, with particular application to moisture diffusion in composite materials. The coupled thermal and moisture diffusion problems are solved by using three‐dimensional finite element method with orthotropic diffusion coefficients and an implicit time‐stepping procedure. Both Frontal and Jacobi conjugate gradient (JCG) solution techniques are used. Numerical examples are presented to illustrate the methodology and include orthotropic diffusivities and multiple material regions. Moisture diffusion within a periodic unit cell of a typical composite material is also considered. The results show that the iterative JCG method is effective and computationally inexpensive to analyze diffusion three‐dimensional diffusion problems with multiple materials.

Multidisciplinary Parametric Design Optimization for Enhancing the Affordability of Molded Composites

The role of design optimization in assisting design decision-making and enhancing the affordability of composite products is studied in this paper. The design of composite products that meet performance, manufacturability, and cost requirements is a multidisciplinary problem. Solutions to appropriately formulated design optimization problems can assist in quickly examining several design alternatives at early conceptual design and parametric design stages. However, the candidate designs require manufacturing process, structural and material performance, and product cost evaluations. These evaluations are often conducted by several domain experts using sophisticated and diverse numerical analysis tools. The formulation of constraint and objective functions in multiple domains, the use of numerical model-based evaluation of the functions, and the solution of multidisciplinary optimization problems during the design of injection molded plastics are addressed in this paper. Numerical examples are presented illustrating the application of optimization techniques in process and exploring material alternatives as well as in parametric design of geometry with affordable cost objectives. A brief description of a software system developed to systematically integrate optimization with the domain-dependent knowledge and geometric design is also presented.