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Illg, W.

Publications and source records attributed to Illg, W..

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Strength of a thick graphite/epoxy rocket motor case after impact by a blunt object

The National Aeronautics and Space Administration is developing graphite/epoxy filament-wound cases (FWC) for the solid rocket motors of the Space Shuttle. The membrane region is about 36 mm thick. A study was made to determine the reduction in strength of the FWC due to accidental damage caused by low-velocity impacts. Two 76.2 cm diameter by 30.5 cm long cylinders were impacted every 5 cm of circumference with 1.27 cm radius impacters of various mass. The impacters represented tools and equipment dropped from various heights. One cylinder was empty and the other was filled with inert propellant. Five cm wide test specimens were cut from the cylinder. Each was centered on an impact sight. The specimens were X-rayed and loaded to failure in uniaxial tension. The strengths and depths of impact damage were analyzed in terms of maximum impact force. Rigid body mechanics and the Hertz law were used to derive an equation for impact force in terms of kinetic energy and the masses of the impacter and target. The depth of damage was predicted in terms of impact force using Love's solution of pressure applied on part of the boundary of a semi-infinite body.

Poe, C. C., Jr.↗
NASA NTRS1986

Effects of partial interlaminar bonding on impact resistance and loaded-hole behavior of graphite/epoxy quasi-isotropic laminates

A partial-bonding interlaminar toughening concept was evaluated for resistance to impact and for behavior of a loaded hole. Perforated Mylar sheets were interleaved between all 24 plies of a graphite/epoxy quasi-isotropic lay-up. Specimens were impacted by aluminum spheres while under tensile or compressive loads. Impact-failure thresholds and residual strengths were obtained. Loaded-hole specimens were tested in three configurations that were critical in bearing, shear, or tension. Partial bonding reduced the tensile and compressive strengths of undamaged specimens by about one-third. For impact, partial bonding did not change the threshold for impact failure under tensile preload. However, under compressive preload, partial bonding caused serious degradation of impact resistance. Partial bonding reduced the maximum load-carrying capacity of all three types of loaded-hole specimens. Overall, partial bonding degraded both impact resistance and bearing strength of holes.

Illg, W.↗
NASA NTRS1986

Tension strength of a thick graphite/epoxy laminate after impact by a 1/2-in. radius impactor

NASA is developing graphite/epoxy filament-wound cases for solid rocket motors of the space shuttle. They are wet-wound with AS4W graphite fiber and HBRF-55A epoxy. The membrane region is about 1.4 inches thick. Two 30-inch-diameter by 12-inch-long cylinders were impacted every two inches of circumference with 1/2-inch radius impactors that were dropped from various heights. One cylinder was empty and the other was filled with inert propellant. Two-inch-wide test specimens were cut from the cylinders. Each was centered on an impact site. The specimens were x-rayed and loaded to failure in uniaxial tension. Rigid body mechanics and the Hertz law were used to predict impact force, local deformations, contact diameters, and contact pressures. The depth of impact damage was predicted using Love's solution for pressure applied on part of the boundary of a semi-infinite body. The predictions were reasonably good. The strengths of the impacted specimens were reduced by as much as 37 percent without visible surface damage. Even the radiographs did not reveal the nonvisible damage.

Poe, C. C., Jr.↗
NASA NTRS1986

Hidden impact damage in thick composites

NASA is developing light-weight graphite/epoxy filament-wound cases (FWC) for the solid rocket motors of the Space Shuttle. The 12-foot-diameter FWC's are about 1.4 inches or more thick. Tests were conducted to determine the tension strength of an FWC after low-velocity impact. Impactors of various kinetic energies, masses, and shapes were used. The conditions that give minimum visual evidence of damage were emphasized. The capability to characterize impact damage with radiography and ultrasonic attenuation was also evaluated. After impact, the specimens were loaded uniaxially in tension to determine residual strengths.

Poe, C. C., Jr.↗
NASA NTRS1985

Prediction of impact force and duration due to low-velocity impact on circular composite laminates

Two simple and improved models - energy-balance and spring-mass - were developed to calculate impact force and duration during low velocity impact of circular composite plates. Both models include the contact deformation of the plate and the impactor as well as bending, transverse shear, and membrane deformations of the plate. The plate was transversely isotropic graphite/epoxy composite laminate and the impactor was a steel sphere. Calculated impact forces from the two analyses agreed with each other. The analyses were verified by comparing the results with reported test data.

Shivakumar, K. N.↗
NASA NTRS1983

Prediction of impact force and duration during low velocity impact on circular composite laminates

Two simple and improved models--energy-balance and spring-mass--were developed to calculate impact force and duration during low velocity impact of circular composite plates. Both models include the contact deformation of the plate and the impactor as well as bending, transverse shear, and membrane deformations of the plate. The plate was transversely isotropic graphite/epoxy composite laminate and the impactor was a steel sphere. Calculated impact forces from the two analyses agreed with each other. The analyses were verified by comparing the results with reported test data.

Shivakumar, K. N.↗
NASA NTRS1983

Analysis of progressive damage in thin circular laminates due to static-equivalent impact loads

Clamped circular graphite/epoxy plates (25.4, 38.1, and 50.8 mm radii) with an 8-ply quasi-isotropic layup were analyzed for static-equivalent impact loads using the minimum-total-potential-energy method and the von Karman strain-displacement equations. A step-by-step incremental transverse displacement procedure was used to calculate plate load and ply stresses. The ply failure region was calculated using the Tsai-Wu criterion. The corresponding failure modes (splitting and fiber failure) were determined using the maximum stress criteria. The first-failure mode was splitting and initiated first in the bottom ply. The splitting-failure thresholds were relatively low and tended to be lower for larger plates than for small plates. The splitting-damage region in each ply was elongated in its fiber direction; the bottom ply had the largest damage region. The calculated damage region for the 25.4-mm-radius plate agreed with limited static test results from the literature.

Shivakumar, K. N.↗
NASA NTRS1979

Fatigue and fracture

The effects of the load/temperature environment of the shuttle on the fatigue life of the body-flap were investigated by conducting real time and accelerated flight-by-flight tests up to 500 flights on coupons containing holes. On the fracture side, much is known about the sensitivity of the tensile strengths of composites to holes and other flaws, predominantly at room temperature. The effects of notches were assessed for graphite/polyimides at the expected temperature extremes of the body-flap: 117K (-250 F) to 589K (600 F). Results indicate that the shuttle temperature extremes may affect fatigue properties HTS/PMR-15. There is no significant effect of temperature on notch-strength. Tensile strengths for specimens with holes and slots are equal.

Illg, W.↗
NASA NTRS1971

Cooperative program for design, fabrication, and testing of graphite/epoxy composite helicopter shafting

The fabrication of UH-1 helicopter tail rotor drive shafts from graphite/epoxy composite materials is discussed. Procedures for eliminating wrinkles caused by lack of precure compaction are described. The development of the adhesive bond between aluminum end couplings and the composite tube is analyzed. Performance tests to validate the superiority of the composite materials are reported.

Wright, C. C.↗
NASA NTRS1965

Infrared shield facilitates optical pyrometer measurements

Water-cooled shield facilitates optical pyrometer high temperature measurements of small sheet metal specimens subjected to tensile stress in fatigue tests. The shield excludes direct or reflected radiation from one face of the specimen and permits viewing of the infrared radiation only.

Eichenbrenner, F. F.↗