ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Oecologia 93 (1993), S. 475-486 
    ISSN: 1432-1939
    Keywords: Coarse woody debris ; Habitat structure ; Palaemonetes ; Refuge ; Risk of predation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract This study demonstrates experimentally that coarse woody debris (CWD) can provide refuge from predation in aquatic habitats. In the Rhode River subestuary of Chesapeake Bay, Maryland, (USA), we (1) measured the abundance of CWD, (2) examined the utilization of CWD by mobile epibenthic fish and crustaceans, and (3) tested experimentally the value of CWD as a refuge from predation. CWD was the dominant above-bottom physical structure in shallow water, ranging in size from small branches (〈2 cm diameter) to fallen trees (〉50 cm diameter). In response to experimental additions of CWD, densities of common epibenthic cpecies (Callinectes sapidus, Fundulus heteroclitus, Fundulus majalis, Gobiosoma bosc, Gobiesox strumosus, Palaemonetes pugio, and Rithropanopeus harrisii) increased significantly compared to control sites without CWD. In laboratory experiments, grass shrimp (P. pugio) responded to predatory fish (F. heteroclitus and Micropogonias undulatus) by utilizing shelter at CWD more frequently than in absence of fish. Access to CWD increased survivorship of grass shrimp in laboratory and field experiments. These experimental results (1) support the hypothesis, commonly proposed but untested for freshwater habitats, that CWD can provide a refuge from predation for epibenthic fish and invertebrates and (2) extend the recognized functional importance of CWD in freshwater to estuarine and marine communities. We hypothesize that CWD is an especially important refuge habitat in the many estuarine and freshwater systems for which alternative physical structure (e.g., vegetation or oyster reefs) are absent or in low abundance.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 2
    facet.materialart.
    Unknown
    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2018-02-23
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 3
    Publication Date: 1993-04-01
    Print ISSN: 0029-8549
    Electronic ISSN: 1432-1939
    Topics: Biology
    Published by Springer
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 4
    Publication Date: 2011-08-18
    Description: A geometrically nonlinear finite element analysis of cohesive failure in typical joints is presented. Cracked-lap-shear joints were chosen for analysis. Results obtained from linear and nonlinear analysis show that nonlinear effects, due to large rotations, significantly affect the calculated mode 1, crack opening, and mode 2, inplane shear, strain-energy-release rates. The ratio of the mode 1 to mode 2 strain-energy-release rates (G1/G2) was found to be strongly affected by the adhesive modulus and the adherend thickness. The ratios between 0.2 and 0.8 can be obtained by varying adherend thickness and using either a single or double cracked-lap-shear specimen configuration. Debond growth rate data, together with the analysis, indicate that mode 1 strain-energy-release rate governs debond growth. Results from the present analysis agree well with experimentally measured joint opening displacements. Previously announced in STAR as N83-13497
    Keywords: STRUCTURAL MECHANICS
    Type: ASME, Transactions, Journal of Engineering Materials and Technology (ISSN 0094-4289); 106; 59-65
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 5
    Publication Date: 2011-08-19
    Description: To analyze the fatigue behavior of a simple composite-to-composite bonded joint, a combined experimental and analytical study of the cracked-lap-shear specimen subjected to constant-amplitude cyclic loading was undertaken. Two bonded systems were studied: T300/5208 graphite/epoxy adherends bonded with adhesives EC 3445 and with FM-300. For each bonded system, two specimen geometries were tested: (1) a strap adherend of 16 plies bonded to a lap adherend of 8 plies, and (2) a strap adherend of 8 plies bonded to a lap adherend of 16 plies. In all specimens tested, the fatigue failure was in the form of cyclic debonding with some 0 deg fiber pull-off from the strap adherend. The debond always grew in the region of adhesive that had the highest mode I (peel) loading and that region was close to the adhesive-strap interface. Furthermore, the measured cyclic debond growth rates correlated well with total strain energy release rates G(T) as well as with its components G(I) (peel) and G(II) (shear) for the mixed-mode loading in the present study.
    Keywords: COMPOSITE MATERIALS
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 6
    facet.materialart.
    Unknown
    In:  Other Sources
    Publication Date: 2011-08-17
    Description: 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.
    Keywords: COMPOSITE MATERIALS
    Type: Graphite/Polyimide Composites; p 259-272
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 7
    Publication Date: 2011-08-19
    Description: The repeatability of debond growth rates in adhesively bonded subjected to constant-amplitude cyclic loading was studied. Debond growth rates were compared from two sets of cracked-lap-shear specimens that were fabricated by two different manufacturers and tested in different laboratories. The fabrication method and testing procedures were identical or both sets of specimens. The specimens consisted of aluminum adherends bonded with FM-73 adhesive. Critical values of strain-energy-release rate were also determined from specimens that were monotonically loaded to failure. The test results showed that the debond growth rates for the two sets of specimens were within a scatter band which is similar to that observed in fatigue crack growth in metals. Cyclic debonding occurred at strain-energy-release rates that were more than an order of magnitude less than the critical strain-energy-release rate in static tests.
    Keywords: STRUCTURAL MECHANICS
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 8
    Publication Date: 2017-09-27
    Description: In this paper the significance of the "small" crack effect as defined in fracture mechanics will be discussed as it relates to life managing rotorcraft dynamic components using the conventional safe-life, the flaw tolerant safe-life, and the damage tolerance design philosophies. These topics will be introduced starting with an explanation of the small-crack theory, then showing how small-crack theory has been used to predict the total fatigue life of fatigue laboratory test coupons with and without flaws, and concluding with how small cracks can affect the crack-growth damage tolerance design philosophy. As stated in this paper the "small" crack effect is defined in fracture mechanics where it has been observed that cracks on the order of 300 microns or less in length will propagate at higher growth rates than long cracks and also will grow at AK values below the long crack AK threshold. The small-crack effect is illustrated herein as resulting from a lack of crack closure and is explained based on continuum mechanics principles using crack-closure concepts in fracture mechanics.
    Keywords: Aircraft Design, Testing and Performance
    Type: Application of Damage Tolerance Principles for Improved Airworthiness of Rotorcraft; 1 - 1 - 1 - 14; RTO-MP-24
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 9
    Publication Date: 2019-06-28
    Description: Fleet readiness and flight safety strongly depend on the degree of reliability that can be designed into rotorcraft flight critical components. The current U.S. Army fatigue life specification for new rotorcraft is the so-called six nines reliability, or a probability of failure of one in a million. The progress of a round robin which was established by the American Helicopter Society (AHS) Subcommittee for Fatigue and Damage Tolerance is reviewed to investigate reliability-based fatigue methodology. The participants in this cooperative effort are in the U.S. Army Aviation Systems Command (AVSCOM) and the rotorcraft industry. One phase of the joint activity examined fatigue reliability under uniquely defined conditions for which only one answer was correct. The other phases were set up to learn how the different industry methods in defining fatigue strength affected the mean fatigue life and reliability calculations. Hence, constant amplitude and spectrum fatigue test data were provided so that each participant could perform their standard fatigue life analysis. As a result of this round robin, the probabilistic logic which includes both fatigue strength and spectrum loading variability in developing a consistant reliability analysis was established. In this first study, the reliability analysis was limited to the linear cumulative damage approach. However, it is expected that superior fatigue life prediction methods will ultimately be developed through this open AHS forum. To that end, these preliminary results were useful in identifying some topics for additional study.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-102757 , NAS 1.15:102757 , AVSCOM-TR-90-B-009
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 10
    Publication Date: 2019-06-28
    Description: Because of the current U.S. Army requirement that all new rotorcraft be designed to a 'six nines' reliability on fatigue life, this study was undertaken to assess the accuracy of the current safe life philosophy using the nominal stress Palmgrem-Miner linear cumulative damage rule to predict the fatigue life of rotorcraft dynamic components. It has been shown that this methodology can predict fatigue lives that differ from test lives by more than two orders of magnitude. A further objective of this work was to compare the accuracy of this methodology to another safe life method called the local strain approach as well as to a method which predicts fatigue life based solely on crack growth data. Spectrum fatigue tests were run on notched (k(sub t) = 3.2) specimens made of 4340 steel using the Felix/28 tests fairly well, being slightly on the unconservative side of the test data. The crack growth method, which is based on 'small crack' crack growth data and a crack-closure model, also predicted the fatigue lives very well with the predicted lives being slightly longer that the mean test lives but within the experimental scatter band. The crack growth model was also able to predict the change in test lives produced by the rainflow reconstructed spectra.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-102759 , NAS 1.15:102759 , AVSCOM-TR-90-B-011 , AD-A239840
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...