Engineering topics

Chamis, Christos C.

Publications and source records attributed to Chamis, Christos C..

At least 235 records · Page 13

NASA NTRS1988

Stress-and-Strain Analysis Of Hot Metal/Fiber Composites

Macroscopic mechanical properties derived from micromechanics. Stress-and-strain equations developed to express microscopic and macroscopic mechanical properties of metals reinforced by unidirectional fibers, over range of temperatures. New equations reduce computational load by providing approximate, closed-form expressions for microscopic and pseudohomogeneous anisotropic properties of single ply reinforced by unidirectional fibers. Typical application is calculation of residual stress in newly manufactured article.

Hopkins, Dale A.↗

NASA NTRS1988

Simplified procedures for designing composite bolted joints

Simplified procedures are described to design and analyze single and multi-bolt composite joints. Numerical examples illustrate the use of these methods. Factors affecting composite bolted joints are summarized. References are cited where more detailed discussion is presented on specific aspects of composite bolted joints. Design variables associated with these joints are summarized in the appendix.

Chamis, Christos C.↗

NASA NTRS1988

Design Procedures for Fiber Composite Box Beams

Step-by-step procedures are described which can be used for the preliminary design of fiber composite box beams subjected to combined loadings. These procedures include a collection of approximate closed-form equations so that all the required calculations can be performed using pocket calculators. Included is an illustrated example of a tapered cantilever box beam subjected to combined loads. The box beam is designed to satisfy strength, displacement, buckling, and frequency requirements.

Chamis, Christos C.↗

NASA NTRS1988

Probabilistic structural analysis to quantify uncertainties associated with turbopump blades

A probabilistic study of turbopump blades has been in progress at NASA Lewis Research Center for over the last two years. The objectives of this study are to evaluate the effects of uncertainties in geometry and material properties on the structural response of the turbopump blades to evaluate the tolerance limits on the design. A methodology based on probabilistic approach was developed to quantify the effects of the random uncertainties. The results indicate that only the variations in geometry have significant effects.

Nagpal, Vinod K.↗

NASA NTRS1988

Finite element substructuring methods for composite mechanics

Finite element substructuring strategies are presented to obtain numerical solutions for three typical problems of interest to the composites community: (1) impact and toughness characterization of composites using Charpy's impact test specimen; (2) free-edge stress analysis of composite laminates; and (3) fracture toughness predictions of composites for individual and combined fracture of modes I, II, and III. The key issue common to these problems is the presence of singular or near singular stress fields. The regions prone to see steep stress gradients are substructured with progressively refined meshes to study the local response simultaneously with the global response. The results from the select examples indicate that finite element substructuring methods are computationally effective for composite singularity mechanics.

Murthy, Pappu L. N.↗

NASA NTRS1988

Hygrothermomechanical fiber composite fatigue: Computational simulation

The technology of advanced composites has matured to the point where these composites are prime contenders for various structural applications. One of the major design considerations for prolonged service of these composites is fatigue due to cyclical hygral (moisture), thermal, and mechanical (hygrothermomechanical) loading conditions. Recent research activities at the NASA Lewis Research Center have led to the development of formal procedures for predicting, using computational simulation, fatigue in fiber composites due to cyclic hygrothermomechanical loading conditions. These formal procedures have subsequently been programmed into a computer module and embedded into the Integrated Composites Analyzer (ICAN) computer code. The objective of this paper is to present and describe results obtained using the augmented ICAN computer code.

Ginty, Carol A.↗

NASA NTRS1988

Application of structural tailoring to spar/shell turboprops

The problem of designing a swept advanced turboprop (ATP) blade for minimum noise output is discussed. Optimal sweep distributions are found using the computer code STAT (Structural Tailoring of Advanced Turboprops). The initial designs are unswept. The blade designs have minimum noise output while satisfying other blade design requirements. The STAT program and the modifications required during this work are described. Parameter studies of the effect of sweep on noise output are also presented.

Rubinstein, Robert↗

NASA NTRS1988

Probabilistic structural analysis of aerospace components using NESSUS

Probabilistic structural analysis of a Space Shuttle main engine turbopump blade is conducted using the computer code NESSUS (numerical evaluation of stochastic structures under stress). The goal of the analysis is to derive probabilistic characteristics of blade response given probabilistic descriptions of uncertainties in blade geometry, material properties, and temperature and pressure distributions. Probability densities are derived for critical blade responses. Risk assessment and failure life analysis is conducted assuming different failure models.

Shiao, Michael C.↗

NASA NTRS1988

Fiber Composite Sandwich Thermostructural Behavior - Computational Simulation

Four computational simulation methods with different levels of sophistication were used to simulate thermal behavior and structural changes of composite sandwich panels with a honeycomb core subjected to a variety of environmental effects. The models on thich these methods are based include three-dimensional finite-element modeling, three-dimensional finite-element modeling assuming a homogeneous core, laminate theory, and simple equations for predicting the equivalent properties of the honeycomb core. A procedure was developed and embedded in a composite mechanics computer code, which made it possile to conduct parametric studies to determine 'optimum' composite sandwich configurations for specific applications. The procedure was applied for the evaluation of composite sandwich behavior at the global, local, laminate, ply, and micromechanics levels when the composite sandwich is subjected to hygral, thermal, and mechanical loading environments.

Chamis, Christos C.↗

NASA NTRS1988

A unique set of micromechanics equations for high-temperature metal matrix composites

A unique set of micromechanic equations is presented for high-temperature metal matrix composites. The set includes expressions to predict mechanical properties, thermal properties and constituent microstresses for the unidirectional fiber reinforced ply. The equations are derived based on a mechanics of materials formulation assuming a square array unit cell model of a single fiber, surrounding matrix and an interphase to account for the chemical reaction which commonly occurs between fiber and matrix. A three-dimensional finite element analysis was used to perform a preliminary validation of the equations. Excellent agreement between properties predicted using the micromechanics equations and properties simulated by the finite element analyses are demonstrated. Implementation of the micromechanics equations as part of an integrated computational capability for nonlinear structural analysis of high temperature multilayered fiber composites is illustrated.

Hopkins, Dale A.↗

NASA NTRS1988

Thermoviscoplastic nonlinear constitutive relationships for structural analysis of high-temperature metal matrix composites

A set of thermoviscoplastic nonlinear constitutive relationships (TVP-NCR) developed for application to high-temperature metal matrix composites (HT-MMC) is described. The structural response of a turbine blade, made from fiber-reinforced superalloy HT-MMC and subject to representative loading conditions, is evaluated. Results indicate that this set of TVP-NCR is computationally effective.

Chamis, Christos C.↗

NASA NTRS1988

Composite interlaminar fracture toughness - Three-dimensional finite-element modeling for mixed mode I, II, and fracture

A computational method/procedure is described which can be used to simulate individual and mixed mode interlaminar fracture progression in fiber composite laminates. Different combinations of Modes 1, 2, and 3 fracture are simulated by varying the crack location through the specimen thickness and by selecting appropriate unsymmetric laminate configurations. The contribution of each fracture mode to strain energy release rate is determined by the local crack closure methods while the mixed mode is determined by global variables. The strain energy release rates are plotted versus extending crack length, where slow crack growth, stable crack growth, and rapid crack growth regions are easily identified. Graphical results are presented to illustrate the effectiveness and versatility of the computational simulation for: (1) evaluating mixed-mode interlaminar fracture, (2) for identifying respective dominant parameters, and (3) for selecting possible simple test methods.

Murthy, Pappu L. N.↗

NASA NTRS1988

Sublaminate- or ply-level analysis of composites and strain energy release rates of end-notch and mixed-mode fracture specimens

The sublaminate or ply-level analysis of composite structures is presently undertaken by a computational procedure yielding the stresses in regions affected by delaminations, transverse cracks, and discontinuities that are related to material properties, geometries, and loads. Attention is given to layers or groups of layers that are immediately affected by flaws; these are analyzed as if they were homogeneous bodies in equilibrium, in isolation from the rest of the laminate. Computed stresses agree with those from a three-dimensional FEM analysis.

Valisetty, Rao R.↗

NASA NTRS1988

Probabilistic structural analysis of aerospace components using NESSUS

Shiao, Michael C.↗

NASA NTRS1987

STAEBL/general composites with hygrothermal effects (STAEBL/GENCOM)

A computer code has been developed to perform structural optimization of turbine blades made from angle ply fiber composite laminates. Design variables available for optimization include geometric parameters such as blade thickness distribution and root chord, and composite material parameters such as ply angles and numbers of plies of each constituent material. Design constraints include resonance margins, forced response margins, maximum stress, and maximum ply combined stress. A general description of this code is given. Design optimization studies for typical blades are presented.

Rubenstein, Robert↗

NASA NTRS1987

ICAN: Integrated Composites Analyzer

Program calculates macromechanical, micromechanical, and related environmental effects. Computer code ICAN developed to carry out comprehensive linear analyses of multilayered fiber composites. Contains essential features required to design structural components made from fiber composites. Code in FORTRAN IV.

Chamis, Christos C.↗

NASA NTRS1987

Design of Fiber Composites for Structural Durability

Hygrothermomechanical effects analyzed by computers. Computational methodology developed and available at NASA Lewis Research Center to design and analyze fiber-composite structures subjected to complex hygrothermomechanical environments. Includes composite mechanics and advanced finited-element structural-analysis methods. Methodology applied to such problems as progressive fracture of composite material, design of composite material for cycle fatigue combined with hot and wet conditions, and general composite-laminate configurations.

Chamis, Christos C.↗

NASA NTRS1987

Simplified composite micromechanics for predicting microstresses

A unified set of composite micromechanics equations is summarized and described. This unified set is for predicting the ply microstresses when the ply stresses are known. The set consists of equations of simple form for predicting three-dimensional stresses (six each) in the matrix, fiber, and interface. Several numerical examples are included to illustrate use and computational effectiveness of the equations in this unified set. Numerical results from these examples are discussed with respect to their significance on microcrack formation and, therefore, damage initiation in fiber composites.

Chamis, Christos C.↗