| The Effect of Loading Parameters on Fatigue of Composite Laminates: Part V |
JUN 2001 |
58 pages |
| Authors:
H. T. Hahn; S. W. Choi; CALIFORNIA UNIV LOS ANGELES DEPT OF MECHANICAL AND AEROSPACE ENGINEERING
|
 | This report is the fifth in a series of reports on the damage growth of notched and visible impact-damaged AS4/3501-6 graphite/epoxy quasi-isotropic laminates under long-term mechanical fatigue loading. The effects of load type, load level, load sequence, and spectrum modification are evaluated in this study. X-ray radiography is taken of the test specimens to monitor the fatigue damage, which are in the form of splitting and delamination around the center ... |
|
| The Effect of Loading Parameters on Fatigue of Composite Laminates: Part IV Information Systems |
DEC 2000 |
77 pages |
| Authors:
H. T. Hahn; Ozgur Turkgenc; CALIFORNIA UNIV LOS ANGELES DEPT OF MECHANICAL AND AEROSPACE ENGINEERING
|
| Damage tolerance, damage resistance and durability assessments of aircraft composite structures are essential components of certification. The certification procedure requires lengthy experimental validation of those assessments, although much research has been conducted to understand the behavior of polymer matrix composites under service conditions. A fair amount of data is available together with a number of analytical models in these areas of research. However, because of the vast number of parameters ... |
|
| Intelligent Processing of Thick Composites |
MAR 1999 |
12 pages |
| Authors:
H. T. Hahn; M. Kang; M. Lin; D. Shin; F. Sonmez; CALIFORNIA UNIV LOS ANGELES DEPT OF MECHANICAL AND AEROSPACE ENGINEERING
|
| Composites consolidation In various manufacturing processes has been studied from a unified point of view to develop a simulation model. As a result a master formulation is now available and can be tailored to each manufacturing process. Process simulation codes have been developed for the resin transfer molding (RTM) and %%autoclave/compression molding processes. The other key results are: (1) development of a finite element code RTMSIM to simulate resin transfer ... |
|
| The Effect of Preloading on Fatigue Damage in Composite Structures: Part 1 |
APR 96 |
44 pages |
| Authors:
H. T. Hahn; Jeffrey L. Timmer; Johthan Bartley-Cho; Seaman Lee; Seung-Gyu Lim; CALIFORNIA UNIV LOS ANGELES DEPT OF MECHANICAL AEROSPACE AND NUCLEAR ENGINEER ING
|
| The effect of preload on damage development in unnotched graphite/ epoxy laminates is studied. Two types of tension-tension fatigue tests were conducted on quasi-isotropic (0/45/-45/90)53, AS-4/3501-6 laminates, and damage was measured in the form of ply cracks. Baseline fatigue tests were run at constant amplitudes ranging from 20% to 60% of the ultimate tensile strength (UTS) while specimens with preloads of 50% to 80% UTS were tested in fatigue at ... |
|
| An Adaptive Time Domain Deconvolution Technique to Characterize Planar Flaws in Highly Attenuative Composites |
SEP 94 |
|
| Authors:
H. A. Huang; C. E. Bakis; H. T. Hahn; A. P. Diwanji
|
 | To identify planar heterogeneities or flaws inside a structure using ultrasonic tests, it is necessary to characterize reflections originating from the boundaries of the heterogeneities. However, for composite materials with high, frequency-dependent wave attenuation, it is often not possible to clearly identify the reflections with either A-scan signals or conventional deconvolution techniques due to the combined effect of signal distortion and overlap. To enable deconvolution of a distorted propagating wave, ... |
|
| Ultrasonic Sol/Gel Processing of Aluminoborosilicate Glass and its Composite with Carbon Fiber Reinforcement |
94 |
|
| Authors:
Song Chiou; H. T. Hahn; CALIFORNIA UNIV LOS ANGELES DEPT OF MECHANICAL AEROSPACE AND NUCLEAR ENGINEER ING
|
| An ultrasonic sol/gel technique has been used to process aluminoborosilicate glass and its composite with carbon fiber reinforcement. In this new technique, ultrasonic energy is used in place of alcohol solvent. Gel time is easily controlled by varying the amount of ultrasonic energy and the resulting gel also exhibits less shrinkage during the densification process. The sonogel-based composite has lower flexural strengths than the alcogel and has close values between ... |
|
| Prediction of Ultrasonic Wave Attenuation in Fiber Reinforced Composite Laminates |
94 |
|
| Authors:
H. A. Huang; C. E. Bakis; H. T. Hahn
|
| The prediction of frequency-dependent wave attenuation in laminated composite materials is essential for the optimization of ultrasonic techniques and test systems. An ultrasonic wave propagating in a composite laminate undergoes absorption and multiple scattering such that the resulting acoustic properties of the laminate are frequency dependent. In this paper, a semi- empirical method is used to predict the frequency dependent wave attenuation coefficients of unidirectional fiber preform and monolithic matrix ... |
|
| The Effects of Processing and Constituent Materials on Compressive Strength of Thick Composite Laminates |
AUG 93 |
42 pages |
| Authors:
H. T. Hahn; E. A. Kempner; J. Slaughter; CALIFORNIA UNIV LOS ANGELES DEPT OF MECHANICAL AEROSPACE AND NUCLEAR ENGINEER ING
|
| The objectives of this study pertain to both the processing of thick composites and the constituent materials used. The main objectives of the research are to identify the processing conditions that are responsible for fiber wrinkling in thick, filament-wound cylinders and to develop a process simulation model for filament winding of thick cylinders. Analysis-experiment correlation will be used to aid model development. Also, the effect of constituent materials on compressive ... |
|
| Impact Monitoring in Smart Composite Structures Using Piezoelectric Sensors |
93 |
|
| Authors:
I. Kim; H. T. Hahn; D. Weems; PENNSYLVANIA STATE UNIV UNIVERSITY PARK
|
| One promising method of monitoring structural integrity of composite structures is based on the use of piezoelectric sensors to detect potentially damage-inducing impact events. The present paper describes the results of a research effort to characterize the performance of piezopolymer sensors in a smart composite structure subjected to low-velocity impact. In order to predict the sensor output signal due to impact, equations describing the piezoelectric behavior of the sensor were ... |
|
| The Stress Development during Filament Winding of Thick Cylinders |
AUG 92 |
34 pages |
| Authors:
H. T. Hahn; S. S. Lee; PENNSYLVANIA STATE UNIV UNIVERSITY PARK DEPT OF ENGINEERING SCIENCE AND MECHA NICS
|
| The stress development during filament winding of thick composite cylinders has been studied using dry glass fiber tows. The thicknesses of the wound cylinders were more than 38 mm while the aluminum mandrel used had an outside diameter of 58 mm. Circumferential winding was used and the winding tension was varied between 4 and 23 N. The radial pressure measured at the mandrel surface using foil gages increased over the ... |
|
| Creep Testing of CVD Silicon Carbide Fibers |
92 |
|
| Authors:
C. A. Lewinsohn; C. E. Bakis; H. T. Hahn; R. E. Tressler; PENNSYLVANIA STATE UNIV UNIVERSITY PARK DEPT OF ENGINEERING SCIENCE AND MECHA NICS
|
| A method for creep testing Textron SCS-6 silicon carbide fibers is described. Creep strains are provided for stresses from 190 to 357 MPa, temperatures from 1200 to 1400 C, and thermal pretreatments of 1300 and 1400 C. It is concluded that the fibers display only primary creep at temperatures between 1200 and 1400 C, at stresses ranging from 190 to 357 MPa, in air, for times as long as 100 ... |
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| Compressive Strength of Carbon Fibers |
JAN 91 |
|
| Authors:
J. M. Prandy; H. T. Hahn; NARMCO MATERIALS INC COSTA MESA CA
|
| Most composites are weaker in compression than in tension, which is due to the poor compressive strength of the load bearing fibers. The present paper discusses the compressive strengths and failure modes of 11 different carbon fibers: PAN-AS1, AS4, IM6, IM7, T700, T300, GY-30, putch-75, ultra high modulus (UHM), high modulus (HM), and high strength (HS). The compressive strength was determined by embedding a fiber bundle in a transparent epoxy ... |
|
| Compressive Strength of Carbon Fibers |
91 |
|
| Authors:
J. M. Prandy; H. T. Hahn; NARMCO RESEARCH AND DEVELOPMENT SAN DIEGO CA*
|
| Most composites are weaker in compression than in tension. This is due to the poor compressive strength of the load bearing fibers. The present paper discusses the compressive strengths and failure modes of 11 different carbon fibers. The compressive strength was determined by embedding a fiber bundle in a transparent epoxy matrix and testing in compression. The resin allows for the containment and observation of failure during and after testing ... |
|
| Compressive Strength of Carbon Fibers |
91 |
|
| Authors:
J. M. Prandy; H. T. Hahn; NARMCO MATERIALS INC COSTA MESA CA
|
| Most composites are weaker in compression than in tension, which is due to the poor compressive strength of the load bearing fibers. This paper discusses the compressive strengths and failure modes of 11 different carbon fibers: PAN-AS1, AS4, IM6, IM7, T700, T300, GY-30, pitch-75, ultra high modulus (UHM), high modulus (HM), and high strength (HS). The compressive strength was determined by embedding a fiber bundle in a transparent matrix of ... |
|
| Compressive Strength of Carbon Fibers |
90 |
|
| Authors:
J. M. Prandy; H. T. Hahn; BASF STRUCTURAL MATERIALS INC ANAHEIM CA*
|
|
| Damage Assessment in Composites by Acousto-Ultrasonic Technique |
DEC 89 |
4 pages |
| Authors:
J. Lee; H. T. Hahn; PENNSYLVANIA STATE UNIV UNIVERSITY PARK COMPOSITES MANUFACTURING TECHNOLOGY C ENTER
|
| Th main objective of the research was to develop and refine the acousto-ultrasonic technique to assess damage in composite materials. Specifically, this research was directed toward three goals: 1) to improve the acousto-ultrasonic technique by focusing on the understanding of the relationship between material properties and wave propagation, 2) to establish operational methods for research and industrial applications, and 3) to improve material characterization and damage assessment using the refined ... |
|
| Prediction and Control of Processing-Induced Residual Stresses in Composites. Part 2. AS4/PEEK Composite |
OCT 89 |
89 pages |
| Authors:
K. J. Schulte; H. T. Hahn; PENNSYLVANIA STATE UNIV UNIVERSITY PARK COMPOSITES MANUFACTURING TECHNOLOGY C ENTER
|
| Residual stresses in symmetric cross-ply laminates were monitored by measuring the dimensionless curvature. The cooling rate was found to have a significant influence on the amount of residual stress in graphite/PEEK (APC-2) laminates. The transverse strain due to crystallization was not negligible and must be considered when predicting residual stresses for cooling rates of 75 deg C/min and lower. The stress-free temperature for O3/90(3) APC-2 laminates decreases with increasing cooling ... |
|
| Effect of Interfacial Properties on Matrix Cracking Stress of Fiber Reinforced Ceramics |
89 |
|
| Authors:
R. A. Shimansky; H. T. Hahn; PENNSYLVANIA STATE UNIV UNIVERSITY PARK COMPOSITES MANUFACTURING TECHNOLOGY C ENTER
|
| Subcritical damage in continuous fiber brittle matrix composites is governed by fiber pullout mechanisms that depend on characteristic strength of the fiber/matrix interface. A predictive tool that approximates the effect of interface properties on matrix cracking stress has been developed for the development and optimization of interface modified composites. Based upon an existing fiber pullout model, an approximate expression for matrix cracking stress is derived. The effects of thermal mismatch, ... |
|
| Ultrasonic Characterization of Sol/Gel Processing |
89 |
|
| Authors:
S. Chiou; H. T. Hahn
|
| The sol/gel process has recently received attention because it enables the production of pure and homogeneous glass without external heating, eliminating the high processing temperatures needed in conventional methods. A disadvantage of the process is that if the rate of evaporation during syneresis is too high, cracking due to mechanical shrinkage can be extensive. A slower evaporation rate produces less cracking, but results in a longer processing time. The key ... |
|
| ultrasonic characterization of sol/gel processing |
89 |
|
| Authors:
S. Chiou; H. T. Hahn
|
| the sol/gel process has recently received attention because it enables the production of pure and homogeneous glass without external heating, eliminating the high processing temperatures needed in conventional methods. to monitor the process, an ultrasonic signal was passed through the material. spectrum changes were measured and then converted to changes in modulus and viscosity, while shrinkage and density changes were monitored using an air-type transducer and an electronic balance. the ... |
|
| A Simplified Analysis of Transverse Ply Cracking in Cross-Ply Laminates |
88 |
|
| Authors:
Y. M. Han; H. T. Hahn; PENNSYLVANIA STATE UNIV UNIVERSITY PARK DEPT OF ENGINEERING SCIENCE AND MECHA NICS
|
| This paper presents a method of analyzing transverse crack initiation and multiplication in symmetric cross-ply laminates. The method is based on the concept of a through-the-thickness inherent flaw and the energy balance principle. With a second-order polynomial assumed for the crack opening displacement, the perturbed stress field due to the presence of ply cracks is determined from the equilibrium conditions. The energy released as a result of ply cracking is ... |
|
| Ultrasonic Cure Characterization of Epoxy Resins: Constitutive Modeling |
OCT 86 |
|
| Authors:
E. J. Tuegel; H. T. Hahn; WASHINGTON UNIV ST LOUIS MO
|
| The use of ultrasound to monitor the cure of epoxy resins have been reported in the lit erature. It has been observed that the speed of the ultrasonic wave increases as the resin cures while the attenuation first increases and then decreases. These changes have been qualitatively explained in terms of the changes in viscosity. In order to use ultrasonic technique to characterize property changes during cure, quantitative relationships between ... |
|
| Compression Failure Mechanisms of Composite Structures |
JUN 86 |
116 pages |
| Authors:
H. T. Hahn; Mohsen Sohi; Suresh Moon; WASHINGTON UNIV ST LOUIS MO CENTER FOR COMPOSITES RESEARCH
|
| An experimental and analytical study was conducted to delineate the compression failure mechanisms of composite structures. Results on unidirectional and quasi-isotropic graphite/epoxy laminates were published previously. The present report summarizes further results on kink band formation in unidirectional composites. In order to assess the compressive strengths and failure modes of fibers themselves, a fiber bundle was embedded in epoxy casting and tested in compression. A total of six different fibers ... |
|
| Compression Failure Mechanisms of Composite Structures. |
JUN 1986 |
|
| Authors:
H. T. Hahn; M. Sohi; S. Moon; WASHINGTON UNIV ST LOUIS MO SCHOOL OF ENGINEERING AND APPLIED SCIENCE
|
| An experimental and analytical study was conducted to delineate the compression failure mechanisms of composite structures. Results on unidirectional and quasi-isotropic graphite/epoxy laminates were published previously. The present report summarizes further results on kink band formation in unidirectional composites. The kink band formation in these composites under compression was studied analytically and through microscopy. The material combinations selected include seven graphite/epoxy composites, two graphite/thermoplastic resin composites, on Kevlar 49/epoxy composite ... |
|
| Compression Failure Mechanisms of Composite Structures, |
JUN 1986 |
|
| Authors:
H. T. Hahn; M. Sohi; S. Moon; WASHINGTON UNIV ST LOUIS MO
|
| An experimental and analytical study was conducted to delineate the compression failure mechanisms of composite structures. Results on kink band formation in unidirectional composites under compression are reported. The material combinations selected include seven graphite/epoxy composites, two graphite/thermoplastic resin composites, one Kevlar 49/epoxy composite and one S-glass/epoxy composite. The dominant mode of failure in all composites was the kink band initiation and propagation. Not only microbuckling, but also compressive failure ... |
|
| Damage Assessment by Acousto-Ultrasonic Techniques in Composites |
APR 86 |
|
| Authors:
Luis Lorenzo; H. T. Hahn; WASHINGTON UNIV ST LOUIS MO CENTER FOR COMPOSITES RESEARCH
|
| This paper addresses the non-destructive evaluation of cross-ply 0/90 subscript 2S and 90/0 subscript 25 S-2 G1/DER 332 laminates using acousto- ultrasonic and acoustic emission techniques. Acoustic emission and acousto- ultrasonic measurements gave early warnings of damage initiation before transverse cracks became visible. AU parameters such as peak amplitude, energy and stress wave factor were equally sensitive to damage initiation but peak amplitude and energy were more sensitive to damage ... |
|
| Damage Assessment by Acousto-Ultrasonic Technique in Composites |
APR 86 |
|
| Authors:
L. Lorenzo; H. T. Hahn; WASHINGTON UNIV ST LOUIS MO
|
| This paper addresses the non-destructive evaluation of cross-ply (0/ 90) sub 2S and (90/0) sub 2S S-2 G1/DER 332 laminates using acousto-ultrasonic and acoustic emission techniques. Acoustic emission and acousto-ultrasonic measurements gave early warnings of damage initiation before transverse cracks became visible. AU parameters such as peak amplitude, energy and stress wave factor were equally sensitive to damage initiation but peak amplitude and energy were more sensitive to damage accumulation. ... |
|
| The Effect of Resin Toughness and Modulus on Compressive Failure Modes of Quasi-Isotropic Graphite/Epoxy Laminates |
MAR 86 |
48 pages |
| Authors:
Mohsen M. Sohi; H. T. Hahn; Jerry G. Williams; NATIONAL AERONAUTICS AND SPACE ADMINISTRATION HAMPTON VA LANGLEY RESEARCH CEN TER
|
| Compressive failure mechanisms in quasi-isotropic graphite/epoxy laminates were characterized for both unnotched and notched specimens and also following damage by impact. Two types of fibers (Thornel 300 and 700) and four resin systems (Narmco 5208, American Cyanamid BP907, and Union Carbide 4901/MDA and 4901/mPDA) were studied. The widely used T300/5208 served as the baseline composite system. For all material combinations, failure of unnotched specimens was initiated by kinking of fibers ... |
|
| The Effect of Resin Toughness and Modulus on Compressive Failure Modes of Quasi-Isotropic Graphite/Epoxy Laminates, |
MAR 1986 |
|
| Authors:
M. M. Sohi; H. T. Hahn; J. G. Williams; NATIONAL AERONAUTICS AND SPACE ADMINISTRATION HAMPTON VA LANGLEY RESEARCH CENTER
|
| Compressive failure mechanisms in quasi-isotropic graphite/epoxy laminates were characterized for both unnotched and notched specimens and also following damage by impact. Two types of fibers (Thornel 300 and 700) and four resin systems (Narmco 5208, American Cyanamid BP907, Union Carbide 4901/MDA and 4901/mPDA) were studied. The widely used T300/5208 served as the baseline composite system. For all material combinations, failure of unnotched specimens was initiated by kinking of fibers in ... |
|
| Hygrothermal Degradation of Sheet Molding Compounds, |
JUN 1985 |
|
| Authors:
A. B. Hosangadi; H. T. Hahn
|
| This paper characterizes the hygrothermal degradation of a sheet molding compound (SMC) containing 65% by weight of E-glass fibers. Six different environments were chosen for the study: room temperature (RT)/65% relative humidity (RH), RT/98% RH, RT/water, 75 deg. C/65% RH, 75 deg. C/65% RH, 75 deg. C/98% RH, and 75 deg.C/water. The extent of degradation was evaluated using visual, microscopic, and chemical analysis techniques. From this study, distinct color changes ... |
|
| Fatigue Failure Mechanisms in Unidirectional Composites, |
OCT 1984 |
|
| Authors:
L. Lorenzo; H. T. Hahn
|
| The tension fatigue behavior of unidirectional composites was studied using model composites where bundles of E-glass and T300 graphite fibers were combind with ductile and brittle epoxies. Model specimens allowed one to monitor and identify the basic failure mechanisms which are difficult to detect in real composite coupons. Fatigue failure modes and the sequence of damage accumulation depended on the stress level. Matrix microcracks between fibers normal to the applied ... |
|
| Detection of Ply Cracking Through Wave Attenuation, |
03 APR 1984 |
|
| Authors:
L. Lorenzo; H. T. Hahn
|
| It is shown that ply cracking of composite laminates can be detected by the change in attenuation of acoustic waves. Ply cracking was induced by loading cross-ply fiberglass S2/epoxy laminates in tension. Two different pi over 4 stacking sequences were used. Acoustic waves were transmitted by using a piezoelectric transducer and were received at a fixed distance by another transducer. Although the peak amplitude was sensitive to the ply cracking, ... |
|
| Effects of Constituent Properties on Compression Failure Mechanisms, |
1984 |
|
| Authors:
H. T. Hahn
|
| Compression failure mechanisms were studied in laminates at three different levels of material construction. The first level is a fiber bundle embedded in epoxy, where the sequence of failure of the fiber bundle can be monitored because the bundle is well contained within the epoxy. The second level is unidirectional laminas loaded in the fiber direction. A comparison between the results from these two levels help in understanding the influence ... |
|
| Effects of Vacuum and Temperature on Mechanical Properties of S2-Glass/Epoxy, |
JAN 1983 |
|
| Authors:
H. T. Hahn; D. G. Hwang; W. K. Chin
|
| Mechanical properties of an S2-glass/epxoy composite were characterized at room temperature and a 100 deg in vacuum. The latter was to simulate the flywheel service environment. The epoxy was DER 332. The composite was filament-wound and cured 2 h at 150 deg. It was found that the composite continues to lose weight even after 150 days of conditioning at 100 deg in vacuum. The composite shows less moisture absorption than ... |
|
| Hygrothermal Expansion of Kevlar 49/Epoxy and S2-Glass/Epoxy Composites, |
NOV 1982 |
|
| Authors:
S. Y. Lo; H. T. Hahn; WASHINGTON UNIV ST LOUIS MO
|
| The hygrothermal expansion properties of Kevlar 49/epoxy and S2 glass/epoxy were studied. The longitudinal and transverse thermal expansion behavior of unidirectional composites and the thickness thermal expansion behavior of pi over 4 laminates were determined for a temperature range of 25-150 degrees C. The results compared favorably with the predictions from a combined micromechanics and laminated plate analysis. One-phase and two-phase diffusion models were used to describe the moisture sorption ... |
|
| Swelling of Kevlar 49/Epoxy and S2-Glass/Epoxy Composites, |
25 OCT 1982 |
|
| Authors:
S. Y. Lo; H. T. Hahn; T. T. Chiao
|
| The moisture effect on the swelling of fiberglass S2/epoxy and Kevlar 49/epoxy was investigated under the environments of 75 deg C/75% RH and 75 deg. C/water. The results indicate that Kevlar 49 fibers swell substantially in the radial direction. Both composites exhibited a change in color after long-time exposure in the environments tested. Kevlar 49/epoxy, was found to be more stable than the fiberglass S2/epoxy. (Author, modified). |
|
| Modeling of Dimensional Stability of Fiber Reinforced Composite Materials, |
JUN 1982 |
|
| Authors:
H. T. Hahn; A. Hosangadi; WASHINGTON UNIV ST LOUIS MO
|
| A review was made of various methods of predicting the expansion and diffusion properties of composite laminates. The analytical complexity and the lack of experimental data for short-fiber composites have been pointed out. However, it is concluded that the prediction equations for continuous-fiber composites can be applied to SMC composites as the effective fiber aspect ratio in the latter is large enough. The effect of hygrothermal expansion on the dimensional ... |
|
| Mechanical Properties of an Aramid Fiber/Epoxy Composite for Flywheel Applications, |
11 JAN 1982 |
|
| Authors:
H. T. Hahn; W. K. Chin
|
| The mechanical properties of a filament-wound Kevlar 49/epoxy composite were characterized under a simulated flywheel service environment of vacuum and 75 degrees C. The five uniaxial static properties and the fatigue properties in longitudinal tension were found to be only slightly affected by the environment. No extraneous weight loss was observed after a long-term exposure to the environment. Both macroscopic and microscopic examinations of failed specimens did not indicate any ... |
|
| Effect of Curing Stresses on the First Ply-Failure in Composite Laminates, |
1982 |
|
| Authors:
R. Y. Kim; H. T. Hahn
|
| An experimental technique of detecting the first ply-failure in laminated composites using a combination of long strain gages and acoustic emission measurement is described. The material system chosen for this study is T300/5208 graphite/epoxy laminates of pi over 4 orientations. The reliability of the techniques was established by visually observing cracks on photomicrographs. Furthermore, the experimental data for all three types of laminates agreed fairly well with the analytical predictions ... |
|
| Residual Stresses and Their Effects in Composite Laminates, |
29 DEC 1981 |
|
| Authors:
H. T. Hahn; D. G. Hwang
|
| The effect of residual stresses on the dimensional stability on composite laminates was studied through the warping of unsymmetric graphite/epoxy laminates while their effect on ply failure was analyzed for Kevlar 49/epoxy laminates. Classical laminated plate theory was used to predict the warping of small and large panels. (Author, modified). |
|
| Flywheel Materials Technology: Design Data Manual for Composite Materials, |
JUL 81 |
|
| Authors:
H. T. Hahn; D. G. Hwang; H. C. Chen; S. Y. Lo; LAWRENCE LIVERMORE NATIONAL LAB LIVERMORE CA
|
| Compiled in this manual are data on thermomechanical properties of unidirectional fiber reinforced composites taken from open literature and government reports. Acknowledgement is extended to the original authors. The primary objective of the manual is to provide the material property data necessary for design of flywheels using modern composite materials. The manual is especially helpful for any design with composites where structural performance is a major concern. Mechanical, flexural and ... |
|
| Flywheel Materials Technology: Design Data Manual for Composite Materials, |
JUL 1981 |
|
| Authors:
H. T. Hahn; D. G. Hwang; H. C. Cheng; S. Y. Lo; LAWRENCE LIVERMORE NATIONAL LAB LIVERMORE CA
|
| Data on thermomechanical properties of unidirectional composites are presented. The data were taken from open literature and government reports. The primary objective of this manual is to provide the material property data necessary for design of flywheels using modern composite materials. However, the manual will be helpful for any design with composites where structural performance is major concern. The characterization of strength and fatigue properties and the hygrothermal properties of ... |
|
| Characterization of Matrix/Interface-Controlled Strength of Unidirectional Composites, |
09 MAR 1981 |
|
| Authors:
H. T. Hahn; J. B. Erikson; S. W. Tsai
|
| A method is presented for characterizing the matrix/interface-controlled strength, including scatter, of unidirectional composites under combined loading. The failure envelope is represented by a second order polynomial and the scatter is described by the strength vector whose magnitude has a Weibull distribution. The method is based on the assumption of failure originating at inherent cracks parallel to the fibers and holds promise as a means of accounting for the size ... |
|
| Failure Characterization of a Graphite/Epoxy Laminate Through Proof Testing, |
12 FEB 1981 |
|
| Authors:
H. T. Hahn; D. G. Hwang
|
| The failure behavior of a pi over 4 AS/3501-5A graphite/epoxy laminate was investigated through proof testing. A primary emphasis was on the delineation of the effect of the proof test on the residual strength and life, the establishment of strength-life relations, and the identification of failure process. The test series consisted of static tests, tension-tension fatigue tests preceded by proof tests, and examinations of failure modes. Major findings are summarized. ... |
|
| Fatigue Failure of Composite Laminates |
FEB 81 |
|
| Authors:
H. T. Hahn; D. G. Hwang; WASHINGTON UNIV ST LOUIS MO DEPT OF MECHANICAL ENGINEERING
|
| The results of an investigation on the tension-tension fatigue behavior of Gr/Ep laminate is summarized. A relation exists between static strength and fatigue life such that a stronger specimen has a longer fatigue life. Thus a minimum fatigue life can be assured by a proof test. The effect of proof test on the subsequent strength and life is not significant. At the 50% probability of survival the S-logN relation is ... |
|
| Fatigue Failure of Composite Laminates, |
28 OCT 80 |
|
| Authors:
H. T. Hahn; D. G. Hwang
|
| The effects of proof testing both on the subsequent strength and on the subsequent fatigue life were delineated and the sources of the scatter in fatigue life were identified. The pi over 4 graphite/epoxy laminate chosen had an average fiber volume fraction of 0.66. Twenty specimens were tested in each test series. Fatigue tests were carried out at the stress ratio of 0.1 and the loading frequency of 5 Hz. ... |
|
| Long-Term Behavior of Composite Materials, |
26 AUG 80 |
|
| Authors:
H. T. Hahn; T. T. Chiao
|
| A two-parameter Weibull distribution was used to analyze the stress- rupture lifetime data spinning over 8 years for Kevlar 49/epoxy and S-glass/ epoxy composites. The results show that, in S-glass/epoxy, a random failure process prevails regardless of the level of applied stress. However, in Kevlar 49/epoxy, the failure above 80% UTS, a wear-out type of failure process is observed. A similar wear-out process also dominates the stress rupture at elevated ... |
|
| Stress-Rupture Lifetimes of Organic Fiber-Epoxy Strands and Pressure Vessels, |
11 FEB 1980 |
|
| Authors:
H. T. Hahn; I. L. Chieu; T. L. Gates
|
| To understand the long-term behavior of filament-wound pressure vessels Kevlar 49/epoxy strands were tested in stress-rupture for more than a year. Because the strands are the smallest structural unit in filament winding, their behavior directly controls the performance of levels. Five different stress levels were studied: 86, 80, 74, 68, and 50% of the mean ultimate tensile strength (UTS). At each stress level, approximately one-hundred strands were hung in a ... |
|
| Crack-tip Damage and Fracture Toughness of Borsic/Titanium Composite |
80 |
|
| Authors:
J. Awerbuch; H. T. Hahn; DREXEL UNIV PHILADELPHIA PA DEPT OF MECHANICAL ENGINEERING AND MECHANICS
|
| The fracture behavior of center-notched unidirectional borsic/ titanium composites under uniaxial tensile loading has been investigated. Load- crack-opening displacement (COD) curves were obtained for crack length-to-width ratios ranging from 0.05 to 0.5. The COD was measured across the crack surfaces by means of laser interferometric displacement gage (gage length of 500 micrometers). As expected, the interferometric displacement gage (IDG) was very sensitive to the appearance of damage at the crack ... |
|
| Environmental Effects on Mechanical Properties of a Kevlar 49/Epoxy Composites, |
80 |
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| Authors:
H. T. Hahn; W. K. Chin; WASHINGTON UNIV ST LOUIS MO MATERIALS RESEARCH LAB
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| The mechanical properties of a Kevlar 49/epoxy composite in a simulated flywheel service environment were determined. The simulated environment of 75 deg. C in vacuum was found to have little effect on static and fatigue properties. While the elevated temperatures of 75 deg. C was not delerterious, the lack of air could be beneficial because it eliminates the possiblity of oxidation. Thus, the elevated temperature of 75 deg. C is ... |
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