On the Use of Quasi-static Testing to Assess Impact Damage Resistance of Composite Shell Structure PDF Download
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Author: Brian Lee Wardle
Publisher:
ISBN:
Category :
Languages : en
Pages : 42
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Book Description
The response of various composite structures to transverse loading was studied through impact and quasi-static testing. The AS4/3501-6 graphite/epoxy composite structures considered have a [±45n/0n]s layup configuration and include convex and concave shell sections, plates, and full cylinders. The impact tests fall within the so-called large-mass, low-velocity regime where previous findings for composite plates indicate that quasi-static tests accurately represent the impact response, i.e., impact and quasi-static tests can be considered equivalent. This equivalence includes damage if the same peak force is reached in both the impact and quasi-static tests. The present work extends the impact and quasi-static equivalence from composite plates to various composite (shell) structures, even when the shell response exhibits an instability. Over nearly the entire range of impact events and shell structures tested, impact and quasi-static response (including damage extent and distribution) is found to be equivalent. A small number of the most flexible (large span, thin) specimens displayed a large-amplitude oscillatory impact loading response which was not observed for the quasi-static tests. These few specimens indicate a regime which may limit the general equivalence of impact and quasi-static testing demonstrated herein. The general equivalence of impact and quasi-static response demonstrated herein for a wide range of composite structures, especially in regard to damage resistance, has important implications for testing and design of damage tolerant aerospace components. Furthermore, the findings suggest that quasi-static experimentation can often be used to simulate the impact response (including damage) of composite shell structures.
Author: Brian Lee Wardle
Publisher:
ISBN:
Category :
Languages : en
Pages : 42
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Book Description
The response of various composite structures to transverse loading was studied through impact and quasi-static testing. The AS4/3501-6 graphite/epoxy composite structures considered have a [±45n/0n]s layup configuration and include convex and concave shell sections, plates, and full cylinders. The impact tests fall within the so-called large-mass, low-velocity regime where previous findings for composite plates indicate that quasi-static tests accurately represent the impact response, i.e., impact and quasi-static tests can be considered equivalent. This equivalence includes damage if the same peak force is reached in both the impact and quasi-static tests. The present work extends the impact and quasi-static equivalence from composite plates to various composite (shell) structures, even when the shell response exhibits an instability. Over nearly the entire range of impact events and shell structures tested, impact and quasi-static response (including damage extent and distribution) is found to be equivalent. A small number of the most flexible (large span, thin) specimens displayed a large-amplitude oscillatory impact loading response which was not observed for the quasi-static tests. These few specimens indicate a regime which may limit the general equivalence of impact and quasi-static testing demonstrated herein. The general equivalence of impact and quasi-static response demonstrated herein for a wide range of composite structures, especially in regard to damage resistance, has important implications for testing and design of damage tolerant aerospace components. Furthermore, the findings suggest that quasi-static experimentation can often be used to simulate the impact response (including damage) of composite shell structures.
Author: Brian Lee Wardle
Publisher:
ISBN:
Category :
Languages : en
Pages : 42
Get Book Here
Book Description
The response of various composite structures to transverse loading was studied through impact and quasi-static testing. The AS4/3501-6 graphite/epoxy composite structures considered have a [±45n/0n]s layup configuration and include convex and concave shell sections, plates, and full cylinders. The impact tests fall within the so-called large-mass, low-velocity regime where previous findings for composite plates indicate that quasi-static tests accurately represent the impact response, i.e., impact and quasi-static tests can be considered equivalent. This equivalence includes damage if the same peak force is reached in both the impact and quasi-static tests. The present work extends the impact and quasi-static equivalence from composite plates to various composite (shell) structures, even when the shell response exhibits an instability. Over nearly the entire range of impact events and shell structures tested, impact and quasi-static response (including damage extent and distribution) is found to be equivalent. A small number of the most flexible (large span, thin) specimens displayed a large-amplitude oscillatory impact loading response which was not observed for the quasi-static tests. These few specimens indicate a regime which may limit the general equivalence of impact and quasi-static testing demonstrated herein. The general equivalence of impact and quasi-static response demonstrated herein for a wide range of composite structures, especially in regard to damage resistance, has important implications for testing and design of damage tolerant aerospace components. Furthermore, the findings suggest that quasi-static experimentation can often be used to simulate the impact response (including damage) of composite shell structures.
Author: Brian Lee Wardle
Publisher:
ISBN:
Category :
Languages : en
Pages : 1162
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Book Description
Work was conducted to explore and begin to understand the impact response of composite shells over a range of impact events considered in the large-mass, low-velocity regime. Both impact and quasi-static experiments were conducted on various structural configurations including convex shells, concave shells, plates, and cylinders with boundary conditions of pinned/no in-plane sliding on the axial edges and free on the circumferential edges. Specimens with a planar aspect ratio of 1 were constructed in [±45n/On]s (n = 1, 2, 3) layups from Hercules AS4/3501-6 graphite epoxy prepreg. Basic structural parameters (radius, span, and thickness) were varied via scaling to determine the effects of these parameters and ratios of these parameters on the response. Damage states were characterized visually and with the dye-penetrant x-ray photography method and compared by defining damage metrics such as the average damage extent and damage extent ratio. An instability phenomenon was noted in the response of many convex shells which has a strong influence on the response. The Hertzian type contact relation does not capture the local response of indented shells and initial stiffness does not characterize the overall shell response. Relative contributions of membrane stiffness and bending stiffness are noted to be key in the overall convex shell response. Boundary conditions were also noted to have a strong influence on the response. Quasi-static and impact response are found to be nearly identical in all respects, including compelling evidence from the damage state comparisons. Two noted differences are that backface spalling was observed for a small number of specimens in impact tests only and that some showed a low frequency, high amplitude response in impact tests which was not observed in quasi-static tests. All structural parameters were shown to affect the response, including the shell height, although thickness was of particular importance. Nondimensional ratios were not found that capture the behavior of convex shells over the entire range of data but the data indicates regimes where different ratios are important, especially the height-to-thickness ratio. Peak force is found to be an excellent damage resistance metric. Impact energy consumption of convex shells through structural deformation, resulting in lower peak forces, is observed to give convex shells improved damage resistance over plate specimens. However, at the barely visible impact damage (BVID) level, convex shells that do not undergo an instability can incur more nonvisible damage than plates at a given force. This damage behavior, which includes different damage distributions, is attributed to differences caused by compressive versus tensile membrane stresses. The general response and resulting local stress and damage state, with relative contributions from both membrane and bending effects, needs to be determined through careful analysis to better determine the important parameters in the response. The damage distribution through the thickness needs to be characterized through experimentation, and then related to the stress state through analysis.
Author: American Institute of Aeronautics and Astronautics
Publisher:
ISBN:
Category : Aeronautics
Languages : en
Pages : 896
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Author:
Publisher:
ISBN:
Category : Chemistry
Languages : en
Pages : 2540
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Author:
Publisher:
ISBN:
Category : Mechanics, Applied
Languages : en
Pages : 400
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Author: Paul A. Lagace
Publisher:
ISBN:
Category :
Languages : en
Pages : 19
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Book Description
Introduction: The aircraft industry continues to pursue the use of advanced composite materials in aircraft structures in order to save weight and produce more efficient, and potentially cost-effective, aircraft. In the more than two decades in which composite materials have been applied, such application to aircraft structures has progressed from secondary structures to "medium-primary" structures and now has pushed into the use in primary structures. The Boeing 777 with its "all-composite" empennage structure represents an important achievement in such regard. However, despite such successes and ambitious programs such as NASA's ACT (Advanced Composite Technology), application of composite materials to the largest parts of the airframe, the wing and fuselage, is still inhibited by a number of issues. Among these issues is the overriding concern of safety. Safety is a very wide-ranging issue. But, with regard to structure, safety generally deals with the ability of the structure to maintain its integrity while subjected to the loads and environment experienced in operation. The central issue in the case of a primary load-bearing structure is damage. There are three facets to this issue of damage: damage resistance, which involves the ability of a structure to undergo events without (minimal) damage occurring and which thus addresses the question "how does damage get there"; damage tolerance, which involves the ability of a structure to undergo loading with damage present without failing and which thus addresses the question of "when does damage propagate/cause failure?"; and damage arrest, which involves the ability of a structural configuration to stop propagating damage before such damage causes catastrophic failure and which thus addresses the question "how can the propagating damage be stopped?". Answers to these three questions must be provided in order for a safe structure to be designed. There are many "events" that can cause damage and must therefore be addressed within the framework just described. A key issue in the design of composite structures is impact [1]. This is of special concern in laminated composite structures due to the relatively low through-thickness strength. Furthermore, the damage caused by impact may be "hidden" beneath the surface of the laminate. Events such as runway kickup, tool drop, encounter with a hailstorm, and engine damage can cause damage in these laminated structures that can result in a significant decrease in their load-carrying capability or can promote further damage growth under cyclic loads thereby reducing the life of the part. It is therefore important to consider the issue of impact, particularly with regard to composite structural configurations that are likely to be utilized in fuselage and wing applications. Since the effects of impact, damage resistance, and damage tolerance are structural responses [2], this must be considered both for generic application as well as with particular structural configurations in mind.
Author: Brian Lee Wardle
Publisher:
ISBN:
Category :
Languages : en
Pages : 25
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Book Description
The experimental impact and quasi-static response, including damage resistance, of various composite shell structures was investigated and reported in a previous document. As an addendum to that original work, the surface damage was characterized. This characterization was in the form of the depth of the dent, which supplements the lengths and area of the visibly damaged region obtained previously. Thus, a three-dimensional characterization of the surface of the impact site was obtained nondestructively. The dent depth measurements are compared with internal damage states previously obtained by the X-radiography technique to better understand the implications of "barely visible impact damage" (BVID). No correlation was found between internal (nonvisible) damage from the X-ray data and the measured characteristics of the surface damage, specifically depth of the dent. In the work previously reported, it was found useful to separate damage data with regard to the presence of shell instability in the response. Peak force was then found to correlate the resulting internal damage for both shell and plate specimens. However, dent depth shows no such general trend or correlation with peak force when the data is separated with regard to the presence of shell instability. This indicates that, for the cases considered, dent depth is not a good indicator of internal damage extent for thin (less than 2.4 mm, or 0.10") composite plate and shell structures.
Author:
Publisher:
ISBN:
Category : Aeronautics
Languages : en
Pages : 980
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Author: Paul A. Lagace
Publisher:
ISBN:
Category :
Languages : en
Pages : 10
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Book Description
A preliminary proposal for a test to determine the (impact) damage resistance of composite materials and their structures is offered. This is centered on the utility of contact force as a parameter directly related to the damage which occurs during the event. This is demonstrated through previously published work as well as via new experiments conducted on various graphite/epoxy material systems and laminates in both monolithic panel and sandwich configurations. Static indentation and impact tests were conducted and show a similarity in the structural and damage responses which occur. This proposal is discussed in terms of the laminates tested and the results obtained, its general applicability, its utility, and issues which need to be addressed further. The proposal makes a significant step towards providing a common reference point and language for (impact) damage resistance.
