George S. Springer

• Stanford University

We introduce the double–double composite layup method and highlight its advantages over the current industry standard layup method. Proof that the double–double (DD) layup method can significantly reduce the required number of plies in laminates and therefore reduce the weight of composite structures is provided. The 4-ply [± ϕ∕± ψ] sub-laminates c...

For the past six years, we have been benefiting from the discovery by [1] that the trace of the plane stress stiffness matrix (tr(Q)) of an orthotropic composite is a fundamental and powerful scaling property of laminated composite materials. Algebraically, tr(Q) turns out to be a measure of the summation of the moduli of the material. It is, there...

An increase in the use of composite materials in areas of engineering has led to a greater demand for engineers versed in the design of structures made from such materials. This book offers students and engineers tools for designing practical composite structures. Among the topics of interest to the designer are stress-strain relationships for a wi...

Models were developed to calculate the mechanical properties of alpine skis. The skis considered are constructed of layers of materials which may include wood, foam, metal, plastics and fibre-reinforced composites. The ski may be manufactured with or without camber and sidecut. On the basis of the models, a computer code was written which yields th...

A propulsion system is introduced for propelling and guiding an object through a liquid. Thrust for forward motion and for turning is produced by acoustic waves generated by piezoelectric ultrasonic transducers. The principle of operation of the transducers and methods for their design are described. Test results are presented that validate the con...

In this investigation, an optical system is introduced for inspecting the interiors of confined spaces, such as the walls of containers, cavities, reservoirs, fuel tanks, pipelines, and the gastrointestinal tract. The optical system wirelessly transmits stereoscopic video to a computer that displays the video in realtime on the screen, where it is...

http://deepblue.lib.umich.edu/bitstream/2027.42/7755/5/bad2319.0001.001.pdf http://deepblue.lib.umich.edu/bitstream/2027.42/7755/4/bad2319.0001.001.txt

http://deepblue.lib.umich.edu/bitstream/2027.42/7751/5/bad2310.0001.001.pdf http://deepblue.lib.umich.edu/bitstream/2027.42/7751/4/bad2310.0001.001.txt

http://deepblue.lib.umich.edu/bitstream/2027.42/7750/5/bad2363.0001.001.pdf http://deepblue.lib.umich.edu/bitstream/2027.42/7750/4/bad2363.0001.001.txt

The use of fiber-reinforced composites from aerospace to civil structures is presented. The potential advantages of composite materials over conventional materials are discussed, the possible advantages being reduced weight, excellent mechanical properties, corrosion resistance, and lower cost. The applications of long and short-fiber composites in...

Preface List of symbols 1. Introduction 2. Displacements, strains, stresses 3. Laminated composites 4. Thin plates 5. Sandwich plates 6. Beams 7. Beams with shear deformation 8. Shells 9. Finite element analysis 10. Failure criteria 11. Micromechanics Appendix A. Cross-sectional properties of thin-walled composite beams Appendix B. Buckling loads a...

Models were developed for calculating the mechanical characteristics and the on-snow performance of snowboards.The snowboards are constructed of layers of materials which may include wood, foam, honeycomb, fibre-reinforced composites and polymeric materials.The models pertaining to the mechanical characteristics provide the bending and torsional st...

We present a method for evaluating the damage in and failure of fiber reinforced composite materials. The method is based on dissipated energy and has three major components: (i) a relationship between the strain in the material and the magnitude of the dissipated energy density, (ii) a model that relates the dissipated energy density to matrix dam...

Submitted to the Department of Aeronautics and Astronautics. Copyright by the author. Thesis (Ph. D.)--Stanford University, 2003.

A model was developed to calculate the turning characteristics of alpine skis. The skis considered are constructed of layers of materials which may include wood, foam, metal, plastics and fibre-reinforced composites. The ski may be manufactured with or without camber and sidecut. The model simulates the motion of a skier of given height, weight and...

The fatigue lives (i.e., the number of cycles to failure) of short fiber reinforced thermoplastic matrix composites were investigated. First, S-N curves were generated at stress ratios of R = 0 and R = -1 for short glass fiber reinforced Copolyamide coupons with 0° (30% or 50% fiber content by weight), 45° (50% fiber content) and 90° (30% or 50% fi...

Tests were conducted measuring the fatigue lives of 150 mm by 10 mm by 2 mm short glass fiber reinforced Copolyamide coupons under different types of cyclic loads. The fatigue lives measured in these tests were compared to those provided by the Generalized Miner’s Rule, and good agreements were found between the test and model results.

The fatigue lives of two different parts (made of short glass fiber reinforced Copolyamide) were investigated. The first one was a 150 mm by 10 mm by 4 mm coupon with a 2 mm hole at the center. The second one was an automotive gear shift link. The fiber orientations and the stresses inside these parts were calculated, respectively, by the commercia...

The fatigue lives of two different parts (made of short glass fiber reinforced Copolyamide) were investigated. The first one was a 150 mm by 10 mm by 4 mm coupon with a 2 mm hole at the center. The second one was an automotive gear shift link. The fiber orientations and the stresses inside these parts were calculated, respectively, by the commercia...

The effectiveness of repair of damaged fiber reinforced composite laminates was investigated; the effectiveness of repair being assessed by the tensile failure load of the repaired laminate. First, tests were conducted measuring the failure loads of laminates repaired either by the scarf, the uniform lap, or the stepped lap technique. Data were gen...

In this investigation, a procedure is developed for determining the effectiveness of composite materials in retrofitting masonry buildings to reduce seismic damage. The reinforcement considered is a thin layer of fiber-reinforced composite applied to the wall in a wallpaper-like fashion. Models were developed which predict the behavior of masonry w...

In a previous paper, models are described for estimating the deformations and failures of masonry walls reinforced with composites when the wall is subjected to static, in-plane shear and normal loads. In this follow-up investigation, tests were performed to assess the accuracies of these models. Three types of test specimens were constructed: i) w...

A technique was developed for simulating the resin transfer molding (RTM) process. The major feature of the technique is a computational steering system that enables the user to make changes during the simulation. Specifically, at any instance, the user can inspect the progress of the resin front. On the basis of the observed resin front position,...

Tests were conducted with the objective of evaluating the effectiveness of techniques used for repairing damaged fiber reinforced laminated composites. Effectiveness of the repair was assessed by the tensile strength of the repaired laminate. In the tests the failure loads of laminates repaired either by the scarf, the uniform lap, or the stepped l...

Models were developed for calculating the failure loads of composite laminates repaired by scarf and uniform lap techniques. The models take into account anisotropy of each ply in the laminate and in the repair ply and non-elastic behavior of the adhesive or resin interlayer between the laminate and the repair patch. On the basis of the models two...

A procedure is presented for determining the layups of unidirectional fiber reinforced composite plates (with or without cutouts) subjected to multiple in-plane and out-of-plane loadsets, such that the plate satisfies the Tsai-Wu Quadratic Strength Failure criterion, is of low weight, and has a layup which is easy to manufacture. Additionally, the...

A model is developed for determining the farfield strains in laminated composites from the strain values indicated by a microsensing device embedded inside the material. The microsensing device considered here consists of three elements: a sensor, a circuit chip, and an antenna. The sensor detects changes in the strains in the material surrounding...

A procedure is described for designing prosthetic implants made of composite materials used in central bone and combined joint and bone replacements. The primary objective was to arrive at an implant made of fiber reinforced composites which has a higher bone growth stimulus and a lower micromotion level than titanium alloy (Ti6A14V) implants curre...

A computer code was developed for simulating the resin transfer molding process. The unique feature of the code is that it is interactive such that, during the simulation process, the user can (a) change the locations of the inlet ports and exhaust vents, and (b) add, remove, open and close ports and vents, and (c) change the inlet pressure of flow...

The drapabilities of uncured unidirectional aligned discontinuous fiber composites were investigated, the drapability being defined as the ratio of the tip deflections, in one minute, of a discontinuous to a continuous fiber reinforced composite cantilevered beam. Equations were developed for calculating the deflections of such composite beams taki...

The development of a hardware/software architecture and interfaces in order to demonstrate command and control functions of amateur satellites through the World Wide web, is initiated. The basic infrastructure of such a system is assembled and validated.

Tests were performed to assess the effects of processing conditions and laminate layup on the change in shape (springback). Twelve inch long and one inch wide coupons made of Fiberite T300/976 graphite/epoxy were tested. Coupons of different layups were cured using different types of molds and different types of vacuum bagging arrangements. The cur...

An experimental technique is described which can be used to measure simultaneously the three principal permeabilities of fiber reforms made of continuous or short fibers. The technique utilizes embedded optical fibers for detecting the position of the liquid front inside the reform. Expressions were derived for calculating the permeabilities from t...

Simple models were developed for determining the vent locations and the fill time of resin transfer molds containing thin flat preforms with isotropic permeabilities. The in-plane shape of the preform is arbitrary and the preform may contain impermeable inserts. The vent locations required to avoid trapping air bubbles are determined by geometric c...

Models are described which simulated the filament winding of thermosetting and thermoplastic matrix composite cylinders. The models relate the processing conditions (applied temperature, pressure and processing speed) to parameters of interest such as composite temperature, viscosity, manufacturing stresses and strains, void sizes, as well as degre...

A method is proposed to predict the future load response of structures made of composite materials. The method makes the predictions on the basis of past loadstrain data. The method was developed for structures subjected to monotonically increasing or to random cyclic tensile loads. A computer code PREDICT was written which, in real time, can provi...

Tests were conducted with continuous glass fiber reinforced epoxy matrix composites that had different types of fiber reinforcements. Composites reinforced with either unidirectional, triaxial or random fibers were tested. The tensile and compressive strengths and moduli, the Iosipescu shear moduli, the short beam shear strengths, the mode I critic...

A semi-empirical model was developed for estimating the growth of delaminations inside fiber reinforced organic matrix composites subjected to cyclic loads. At any point on the circumference of the delamination mode I, mode II or mixed mode conditions may exist. The form of the proposed delamination growth model follows Elber's expression for the g...

The changes in shapes of fiber-reinforced composite beams, plates and shells affected by embedded piezoelectric actuators were investigated. An analytical method was developed which can be used to calculate the changes in shapes for specified applied voltages to the actuators. The method is formulated on the basis of mathematical models using two-d...

The changes in shapes of fiber-reinforced composite beams, plates and shells affected by embedded piezoelectric actuators were investigated. An analytical method was developed to determine the voltages needed to achieve a specified desired shape. The method is formulated on the basis of mathematical models using two-dimensional, linear, shallow she...

A model is presented which describes the reponse of organic matrix composites to hot and moist environments. Equations are presented for calculating the temperature and moisture distributions, the total moisture content, and the hygrothermal deformations of composite laminates. Methods for measuring the relevant material properties are described. A...

A method is presented for calculating the locations, shapes, and sizes of delaminations which occur in a fiber reinforced composite plate subjected to transverse static or dynamic (impact) loads. The plate may be simply supported, clamped, or free along its edges. A model of the delamination formation was developed. This model was then coupled with...

The use of strain sensors in detecting delaminations in fiber reinforced composite laminates was investigated. Tests were performed with (04/904)s, (06/902)s, and (03/453 - 453)s plates made of Fiberite T300/976 unidirectional graphite-epoxy tape. Strain gauges were mounted on the surfaces as well as inside the plates. The plates were subjected to...

The use of embedded intrinsic Fabry-Perot sensors in measuring strains and temperature changes was explored. Tests were performed with intrinsic Fabry-Perot sensors embedded in plates made of Fiberite T300/976 graphite-epoxy and of Fiberite APC2-PEEK graphite thermoplastic unidirectional tapes. The plates were also in strumented with thermocouples...

A finite element was developed to calculate the behavior of an axisymmetric composite body of revolution impacting on an isotropic surface. The composite is made of unidirectional fiber reinforced plies, with no restriction either on the number of plies or on the orientation of the fibers in each ply; hence the laminate may be 'thin' or 'thick', an...

A model was developed for embedded intrinsic and extrinsic Fabry-Perot fiber optic sensors. This model relates the strains and the temperature changes in the material surrounding the sensor to the reflected light intensity. The model consists of three parts. Submodel I relates the temperature and the strains in the material to the temperature and t...

Tests were performed to measure the failure loads of axially compressed glass-fiber-reinforced and graphite-fiber-reinforced composite cylinders. The data were compared with the results of a previous model, which was based on a three-dimensional stress analysis and the Tsai-Wu quadratic first-ply failure criterion. This model predicted the failure...

Tests were performed measuring the locations and geometries of delaminations in Fiberite T300/976 graphite/epoxy, Fiberite IM7/977-2 graphite-toughened epoxy, and ICI APC-2 graphite/PEEK plates subjected to transverse impact loads. The data provide specific information on the effects of impactor velocity, impactor mass, material, thickness of back...

A stress analysis of fiber-reinforced composite cylinders and cylindrical segments is presented. The analysis applies to thin as well as to thick walled cylinders with no restriction on fiber orientation, other than that an individual fiber must remain at the same radial distance from the axis. The cylinder may be subjected to hygrothermal and mech...

Tests were performed measuring the damage initiation loads and the loca tions, shapes, and sizes of delaminations in Fiberite T300/976 graphite/epoxy, Fiberite IM7/977-2 graphite-toughened epoxy, and ICI APC-2 graphite-PEEK plates subjected to transverse static loads. The data were compared to the results of the Finn-Springer model, and good agreem...

In-plane compressive and three-point bend tests were performed to evalu ate the strengths of composite laminates containing embedded sensors. Unidirectional, cross-ply and quasi-isotropic specimens were fabricated using Fiberite T300/976 or Fiberite APC-2 unidirectional tape. A thermocouple or a strain gauge was embedded at the center of the specim...

Two separate contributions to the state-of-the-art in on-line (out- of-autoclave) consolidation of thermoplastic matrix composites have been developed under this program. First, an induction consolidation sensor has been developed which appears capable of detecting differences in consolidation state without physical contact. The consolidation defec...

Tests were performed assessing the effectiveness of repair in restoring the mechanical properties of damaged, solid composite plates made either of Fiberite T300/976 graphite-epoxy, Fiberite IM7/977-2 graphite-toughened epoxy, or ICI APC-2 graphite-PEEK. The plate length, the layup and the amount of damage were also varied. Damage was introduced in...

The high temperature behavior of carbon-phenolic and carbon-carbon composites was investigated. Models were developed which describe the thermal and me chanical responses of such composites when rapidly heated to high temperatures. On the basis of the models, a computer code was written that provides the temperature and pressure distributions, vapo...

Tests were conducted to validate the model and the CHAR computer code previously developed for calculating the thermomechanical behavior of carbon-phenolic and carbon-carbon composites exposed to high temperatures. Temperature distributions in and damage of rapidly heated carbon-phenolic composites were measured. The data com pared well to the resu...

Models for autoclave curing of thermosetting matrix composites are briefly described along with models of manufacturing process models for thermoplastic matrix composites. These models can be used to obtain optimum cure cycles of composite materials. They are particularly useful since the cure cycle must be modified to account for the effect of int...

Tests were performed measuring the temperature, ionic conductivity, and compaction in 16 to 200 ply thick graphite-epoxy laminates made of either Fiberite T300/976 (tape or fabric) or Hercules AS/3501-6 (tape). The data were compared to results calculated by the Loos-Springer CURE model. Good agreement was found between the model results and the da...

Tests were conducted to validate the thermoplastic manufacturing process models described by Mantell and Springer. In the tests, APC-2 graphite/PEEK plates were fabricated both in a press and with a specially constructed tape laying apparatus. The temperature, intimate contact and bonding inside the plates were measured. The data agreed well with t...

Models were developed which simulate the processing of thermoplastic matrix composites. The models relate the applied temperature, pressure, speed, and time to the temperature, crystallinity, consolidation, interlaminar bonding, and residual stresses and strains inside the composite. The formulations follow the models proposed by Springer, Loos, an...

A model and a computer code were developed for calculating the thermal, chemical, and mechanical behaviors of carbon-phenolic and carbon-carbon composites heated rapidly to high temperatures. The model and the computer code (termed CHAR) were validated by the results of thermochemical and mechanical tests on FM5055 carbon-phenolic cloth. The result...

A finite element computer code was developed for calculating the stresses and strains in, and elongations of, racetrack shaped composite straps loaded by two pins in tension. A procedure was also established for estimating the failure loads of such straps, by utilizing the results provided by the finite element method and the Tsai-Wu failure criter...

A finite element code was developed for calculating stresses and strains in thick, curved composite laminates subjected to an arbitrary, but consistent, combination of forces and displacements. The laminate may be arbitrarily curved in one plane but must have no curvature in the other two perpendicular planes. The analysis was formulated using anis...

A model is presented describing the pultrusion process of thermoplastic matrix composites. The model provides the temperature, crystallinity, pressure, and consolidation inside the composite along the axis of the die, and the required pulling force. On the basis of the model, a computer code was written that can be used to obtain numerical results....

A rule based expert system was developed for controlling the autoclave temperature and pressure during cure of fiber reinforced thermosetting matrix composites. Rules were established which ensure that the temperatures and pressures remain within the required limits, the laminate is fully compacted and fully cured, the void content is minimum, and...

A technique is described for determining the mechanical properties of thick composite laminates. According to this technique the test specimens are cut out from thin sublaminates separated from the main laminate by porous Teflon sheets. Data are presented which show the usefulness of the method in measuring tensile, compressive and short beam shear...

Teas were conducted measuring the deformations of composite open cylindrical shells subjected to temperature changes. The cylindrical shells were made of 16 plies of Fiberite T300/934 unidirectional graphite-epoxy tape arranged as cither [02/902]2, or [902/02)2,. The measured deformations were compared to the results of a higher order shell...

The behavior of elliptical sublaminates created by delaminations in composite plates was investigated for plates subjected to in-plane compressive, shear, and thermal loads. The axes of the ellipse may be arbitrarily oriented with respect to the applied loads. A model was developed which provides the stresses, strains, and displacements of the subl...

The present volume on impact damage in composite plates presents an extensive compendium of visual and graphic data regarding a variety of material and impactor parameters. The photographs are taken with X-ray and C-scan imaging in conjunction with a dye penetrant to show matrix cracks and delaminations. Impact and static-loading tests are performe...

A model was developed for simulating the manufacturing process of filament-wound cylinders made of a thermoset matrix composite. The model relates the process variables (winding speed, fiber tension, applied temperature) to the parameters characterizing the composite cylinder and the mandrel. The model is applicable to cylinders for which the diame...

A model was developed which describes the filament winding process of composite cylinders. The model relates the significant process variables such as winding speed, fiber tension, and applied temperature to the thermal, chemical and mechanical be havior of the composite cylinder and the mandrel. Based on the model, a user friendly code was written...

Analytical and experimental studies were performed to validate the model developed by Lee and Springer for simulating the manufacturing process of filament wound composite cylinders. First, results calculated by the Lee-Springer model were com pared to results of the Calius-Springer thin cylinder model. Second, temperatures and strains calculated b...

By using the Lee-Springer filament winding model temperatures, degrees of cure, viscosities, stresses, strains, fiber tensions, fiber motions, and void diameters were calculated in graphite-epoxy composite cylinders during the winding and subsequent cur ing. The results demonstrate the type of information which can be generated by the model. It is...

The conceptual evolution of waverider configurations and their applications to hypersonic air vehicles are examined in the context of evolving mission requirements and technological advances. The fundamental objective of employing configurations which tend to maximize the payload fraction is emphasized, and the achievement of this objective over th...

A numerical procedure is presented for calculating the hygrothermal stresses and strains in laminated composite shells of revolution with axisymmetric temperature and moisture distributions. The procedure is based on a shell theory developed previously by Doxsee, and utilizes a displacement-based finite element method of solution of the governing e...

Equations are derived which describe the free damped vibrations of plates and shells made of laminated fiber-reinforced, organic-matrix composites. A finite element method is developed for obtaining solutions to these equations. A computer code is written, which can be used to calculate the natural frequencies, mode shapes, and damping factors of r...

The response of delaminated composite plates to compressive in-plane loads was investigated. The delaminated region may be either circular or elliptical, and may be located between any two plies of the laminate. For elliptical delaminations, the axes of the ellipse may be arbitrarily oriented with respect to the applied loads. A model was developed...

A model is presented for estimating the dimensions of delaminations in continuous fiber reinforced composite plates subjected to non-penetrating (low velocity) impact of a solid object. The model is based on dimensional analysis, and results in two simple, closed form expressions, one providing the delamination length, the other the delamination wi...

Models are presented for describing the stress-strain relationships and the strengths of a thermoset matrix composite exposed to elevated temperature. The models take into account the nonlinear elastic characteristics of the material. For Fiberite 976 resin and for unidirectional Fiberite T300/976 composite the constants required in the models were...

Models are presented for describing the time dependent viscoelastic and viscoplastic stress-strain relationships of unidirectional fiber reinforced thermoset matrix composites exposed to elevated temperatures. For Fiberite T300/976 graphite-epoxy com posite the constants in the stress-strain relationships were determined from data obtained in four...

A method is presented for analyzing the free damped vibration characteristics of plates, cylinders, and cylindrical panels made of fiber reinforced, organic matrix composites. A computer code is described that can be used to calculate the natural frequencies, mode shapes, and damping factors of plates, cylinders, and cylindrical panels with free, c...

Tests were conducted to determine the moisture absorption characteristics of PEEK 150P polymer and APC-2 composite exposed to humid air, and to evaluate the effects of moisture content and crystallinity on the fracture toughness. Tests were con ducted with PEEK 150P specimens having 30, 34, and 43 percent crystallinities and with APC-2 specimens ha...

Tests were performed to evaluate the usefulness of dielectric techniques in monitoring the cure of thermoset matrix composites. Using a Micromet Instrument Eumetric System II microdielectrometer, signals related to the permittivity and loss factor of the material were recorded during the cure of Fiberite T300/976 and Hercules AS/3501-6 graphite epo...

A model is presented of the steps involved in the manufacturing process of semicrystalline thermoplastic matrix composites. The model relates the temperature and pressure applied during processing to (a) the flow of the matrix into the fiber tow, (b) the formation of contact and bond between adjacent plies, and (c) the crystallinity. The results of...

Tests were performed to verify a previously developed model for simulating the manufacturing process of filament wound cylinders. The axial and hoop strains were measured during cure inside a filament wound Fiberite T300/976 graphite-epoxy cylinder. The measured strains were compared to those computed by the model. Good agreements were found betwee...

Tests were performed measuring the locations and extents of delaminations and matrix crackings in 3-in. by 3-in. Fiberite T300/934 graphite/epoxy plates impacted by 1/2-in. diameter aluminum spheres. Plates with six ply orientations were tested. The impactor speeds ranged from 700 to 1300 in/sec. The plates were inspected by C-scan both before and...

A method is presented for calculating the locations and sizes of delaminations which occur in a rectangular, fiber reinforced composite plate subjected to nonpenetrating (low velocity) impact of a solid object. The plate may be simply supported or clamped along its edges. In-plane loads or in-plane strains may be imposed on the plate during the imp...

A model is presented for describing the nonlinear, elastic behavior of unidirectional organic matrix composites at elevated temperatures. The model describes the longitudinal and transverse tensile, longitudinal and transverse compressive, and shear stress-strain relationships, as well as the Poisson ratios. Tests were performed in the temperature...

Tests were performed to evaluate the effects of moisture and temperature on the com pressive and short beam shear properties of Fiberite T300/976 fabric. The maximum mois ture content was measured as a function of relative humidity and temperature. The diffusivity was determined as a function of temperature. The compressive and short beam shear str...