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COMPOSITES AND PLASTICS - Click here to return to overview or click on a title to download the document
- Alternate Test Methods for Determining Mechanical Properties of Graphite Epoxy Materials,
Authors: Michael J. Viens, Goddard Space Flight Center
Language: English
He work performed for this memorandum investigated the use of three devices which could potentially reduce both cost and turn around time for testing graphite epoxy (Gr/Ep) tensile coupons. Gr/Ep test coupons are typically tabbed to facilitate load transfer to the test coupon and are strain gauged to determine stiffness and strain at failure of the test coupon. The implementation of the aforementioned devices would eliminate the need for both test tabs and the strin gauges. The tensile loading of tabless coupons was performed using hydraulic grips with hybrid wedge surfaces to transfer load the test coupons. The strain in the test coupons was monitored using a laser extensometer. The coupon stifness was measured prior to tensil testing with a sonic resonance measurement system. This memorandum reports the results of these tests and compares the strength results to that of prvious tests and the strain results obtained using strain gauges.
- Degradation und Erholung der Verformungsmoduli von Polycarbonat unter mechanische Last
Authors: Rainer Tilgner, Infineon Technologies
Language: German
Am Beispiel der Veränderung der Verformungsmoduli von Polycarbonat unter mechanischer Last wird die Notwendigkeit einer derartigen Bestimmung für eine moderne Konstruktionstechnik verdeutlicht. Dazu wird neben einfachen statischen Belastungstests eine dynamische Meßmethode, die das Schwingungsverhalten von Probekörpern verfolgt, beschrieben. Gerade der zeitliche Verlauf von Degradation und Erholung verdeutlicht deren Bedeutung für Sicherheits- und Zuverlässigkeitsaspekte moderner Aufbautechnik.
- Determination of Elastic Moduli of Fiber-Resin Composites Using an Impulse Excitation Technique
Authors: Michael J. Viens, Jeffrey J. Johnson
Language: English
The elastic moduli of graphite/epoxy and graphite/cyanate ester composite specimens with various laminate lay-ups was determined using an impulse excitation/acoustic resonance technique and compared to those determined using traditional strain gauge and extensometer techniques. The stiffness results were also compared to those predicted from laminate theory using unaxial properties. The specimen stiffness interrogated ranged from 12 to 30 Msi. The impulse excitation technique was found to be a relatively quick and accurate method for determining elastic moduli with minimal specimen preparation and no requirement for mechanical loading frames. The results of this investigation showed good correlation between the elastic modulus determined using the impulse excitation technique, strain gauge and extensometer techniques, and modulus predicted from laminate theory. The flexural stiffness determined using the impulse excitation was in good agreement with that predicted from laminate theory. The impulse excitation/acoustic resonence interrogation technique has potential as a quality control test.
- Development of ZrO2 -ZrB2 composites
Authors: B. Basu, J. Vleugels, O. Van Der Biest
Language: English
Yttria-stabilised tetragonal zirconia (Y-TZP) composites with 30 vol.% ZrB2 are prepared by hot pressing in vacuum for 1 h at 1450°C. Different commercial zirconia starting powders as well as a range of ZrO2 'powder mixture' grades, based on co-precipitated powders were used for the composite production. The measured differences in the mechanical properties of the obtained composites is explained in terms of the microstructure, the residual stresses due to the presence of ZrB2 , and the stabiliser content and its distribution. While the stabiliser content and distribution remained significant, the residual stress in the zirconia matrix is found to be an important additional factor influencing the tetragonal zirconia transformability. Crack deflection by the ZrB2 phase was identified as an active toughening mechanism in the composites.
- Etude des relations Structure - Propriétés mécaniques de thermoplastiques renforcés par des particules inorganiques Nanoscopiques
Authors: Emmanuelle Reynaud, INSA Lyon
Language: French
- Particulate-Reinforced Titanium Alloy Composites Economically formed by Combined Cold and Hot Isostatic Pressing,
Authors: Stanley Abkowitz, Paul F. Weihrauch, Susan M. Abkowitz, Dynamet Technology Inc.
Language: English
- Toughness Optimisation of ZrO2-TiB2 composites
Authors: B. Basu, J. Vleugels and O. Van Der Biest, Key Engineering Materials Vols. 206-213 (2002) pp. 1177-1180
Language: English
Yttria-stabilised tetragonal zirconia (Y-TZP) composites with 30 vol. % TiB2 are fabricated by hot pressing in vacuum for 1 hour at 1450°C. Commercial co-precipitated zirconia starting powder as well as a range of experimental powder mixture grades of monoclinic and coprecipitated 3Y-TZP powders was used to study the influence of the zirconia matrix composition on the fracture toughness of the composites. The observed variation in mechanical properties of the composites is explained in terms of the microstructure, the residual stresses due to the presence of TiB2 and the stabiliser content. Whereas the overall yttria content is very crucial, the residual stress is found to be an additional important parameter influencing the t-ZrO2 transformability that needs to be taken into account when optimising the toughness of the composites. Beside transformation toughening, crack deflection was identified as an active toughening mechanism in the composites. A simple approach to tailor the toughness of ZrO2-TiB2 composites is proposed.
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