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The experimental and analytical efforts being undertaken to investigate the response of composite and aluminum structures under crash loading conditions were reviewed. A Boeing 720 airplane was used in the controlled-impact demonstration test. Energy absorption of composite materials, the tearing of fuselage skin panels, the friction and abrasion behavior of composite skins, and the crushing behavior and dynamic response of composite beams were among the topics addressed.

A method is introduced to identify an unknown impact on a composite plate. The identification includes the impact location and force time history. A distributed piezoelectric sensor array measures the plate response to the impact. An optimization technique solves the identification problem. The technique identifies the impact by comparing the calculated model response to the measured response. The identification method was implemented in the computer code IDIMPACT. To verify the identification system, many impacts were distributed on a 36-inch by 30-inch composite plate with a distributed surface-mounted piezoelectric sensors. The code proved to be a reliable and accurate identification system. The average error in the reported impact was .56 inch, and the average error in the energy of the force reconstruction was 15%.

A method is introduced to identify an unknown impact on a composite plate. The identification includes the impact location and force time history. A distributed piezoelectric sensor array measures the plate response to the impact. An optimization technique solves the identification problem. The technique identifies the impact by comparing the calculated model response to the measured response. The identification method was implemented in the computer code IDIMPACT. To verify the identification system, many impacts were distributed on a 36-inch by 30-inch composite plate with a distributed surface-mounted piezoelectric sensors. The code proved to be a reliable and accurate identification system. The average error in the reported impact was .56 inch, and the average error in the energy of the force reconstruction was 15%.

The effect of low velocity impact on the strength of laminates fabricated from graphite/epoxy and Kevlar 49/epoxy composite materials was studied. The test laminates were loaded statically either in uniaxial tension or compression when impact occurred to evaluate the effect of loading on the initiation of damage and/or failure. Typical aircraft service conditions such as runway debris encountered during landing were simulated by impacting 1.27-cm-diameter projectiles normal to the plane of the test laminates at velocities between 5.2 and 48.8 m/s.

The experimental and analytical efforts being undertaken to investigate the response of composite and aluminum structures under crash loading conditions were reviewed. A Boeing 720 airplane was used in the controlled-impact demonstration test. Energy absorption of composite materials, the tearing of fuselage skin panels, the friction and abrasion behavior of composite skins, and the crushing behavior and dynamic response of composite beams were among the topics addressed.

The compressive behavior of a graphite/epoxy (AS-3501-6) composite system is studied here experimentally and analytically. First, a test method is developed using a flat-end specimen. Tests are then performed for six (6) different composite laminates. In each case, the variation of the test temperature ranges from -12 C to 121 C while the variation of the moisture content in the specimens ranges from dry to saturated-wet. Two cases of dry/wet/dry conditioned specimens are also studied. An analytical model which is based on the concept of microbuckling is developed to predict the compression strength of unidirectional laminates. The analytical results compare well with experiment. The rule-of-mixture method is shown to predict the compressive strength of laminates of complex lay-ups. (Author)

The effect of low velocity projectile impact on sandwich-type structural components was investigated. The materials used in the fabrication of the impact surface were graphite-, Kevlar-, and boron-fibers with appropriate epoxy matrices. The testing of the specimens was performed at moderately low- and high-temperatures as well as at room temperature to assess the impact-initiated strength degradation of the laminates. Eleven laminates with different stacking sequences, orientations, and thicknesses were tested. The low energy projectile impact is considered to simulate the damage caused by runway debris, the dropping of the hand tools during servicing, etc., on the secondary aircraft structures fabricated with the composite materials. The results show the preload and the impact energy combinations necessary to cause catastrophic failure in the laminates tested. A set of faired curves indicating the failure thresholds is shown separately for the tension-and compression-loaded laminates. The specific-strengths and -modulii for the various laminates tested are also given.

The objective of this project was to model the 5-3/4 inch pressure vessels used on the NASA RTOP program in an attempt to learn more about how impact damage forms and what are the residual effects of the resulting damage. A global-local finite element model was developed for the bottle and the states of stress in the bottles were determined down to the constituent level. The experimental data that was generated on the NASA RTOP program was not in a form that enabled the model developed under this grant to be correlated with the experimental data. As a result of this exercise it is recommended that an experimental program be designed using statistical design of experiment techniques to generate data that can be used to isolate the phenomenon that control the formation of impact damage. This data should include residual property determinations so that models for post impact structural integrity can be developed. It is also recommended that the global-local methodology be integrated directly into the finite element code. This will require considerable code development.

The compressive behavior of a graphite/epoxy (As-3501-6) composite system is studied here experimentally and analytically. First, a test method is developed using a flat end specimen. Tests are then performed for six (6) different composite laminates. In each case, the variation of the test temperature ranges from -12 C to 121 C while the variation of the moisture content in the specimens ranges from dry to saturated wet. Two cases of dry/wet/dry conditioned specimens are also studied. An analytical model which is based on the concept of microbuckling is developed to predict the compression strength of unidirectional laminates. The analytical results compare well with experiment: The rule-of-mixture method is shown to predict the compressive strength of laminates of complex lay-ups.

The compressive behavior of a graphite/epoxy (As-3501-6) composite system is studied here experimentally and analytically. First, a test method is developed using a flat end specimen. Tests are then performed for six (6) different composite laminates. In each case, the variation of the test temperature ranges from -12 C to 121 C while the variation of the moisture content in the specimens ranges from dry to saturated wet. Two cases of dry/wet/dry conditioned specimens are also studied. An analytical model which is based on the concept of microbuckling is developed to predict the compression strength of unidirectional laminates. The analytical results compare well with experiment: The rule-of-mixture method is shown to predict the compressive strength of laminates of complex lay-ups.