Lundsgaard-Larsen, C.

Sørensen, Bent F.

Wahlgren, Søren

Online Research Database In Technology

                       General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.  • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal   If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.     Downloaded from orbit.dtu.dk on: Dec 19, 2017Cyclic crack propagation  and - arrest in a unidirectional polymer matrix compositeexhibiting large scale bridgingWahlgren, Søren; Sørensen, Bent F.; Lundsgaard-Larsen, C.Published in:ProceedingsPublication date:2011Link back to DTU OrbitCitation (APA):Wahlgren, S., Sørensen, B. F., & Lundsgaard-Larsen, C. (2011). Cyclic crack propagation  and - arrest in aunidirectional polymer matrix composite exhibiting large scale bridging. In Proceedings (pp. TH24-2)18th International Conference on composite materials CRACK PROPAGATION AND -ARREST IN A UNIDIRECTIONAL POLYMER MATRIX COMPOSITE EXHIBITING LARGE SCALE BRIDGING   Søren Wahlgren1, Bent F. Sørensen2 and Christian Lundsgaard-Larsen3  1LM Wind Power, Vingen 1, 6640 Lunderskov, Denmark Email: sqwa@risoe.dtu.dk, web page: http://www.risoe.dk  and swah@lmwindpower.com, web page: http://www.lmwindpower.com   2Materials Research Division, Risø DTU, Frederiksborgvej 399, 4000 Roskilde, Denmark. Email: bsqr@risoe.dtu.dk, web page: http://www.risoe.dk  3LM Wind Power, Vingen 1, 6640 Lunderskov, Denmark Email: clla@lmwindpower.com, web page: http://www.lmwindpower.dk  Keywords: Composite mechanics, fracture mechanics, fatigue, cohesive law    ABSTRACT  Unidirectional laminate double cantilever beam specimens were subjected to mode I fracture in cyclic loading using a novel test setup based on pure bending moments. Crack propagation was studied with the aim of identifying a cyclic cohesive law representing large-scale fiber cross over bridging as a function of the applied load level. It was found that the crack propagation occurred relatively fast in the first load cycles, followed by a transient situation where crack growth rate decreases as a crack bridging zone develops from the initial notch to the crack tip. For loads over a certain threshold, a lower steady state crack growth velocity is attained as the bridging zone is fully developed; then the crack bridging zone propagates along the specimen at the same rate as the crack tip. For loads below this threshold, the crack propagation rate continually decreases and do not reach steady state crack growth. Rates for initial as well as steady state crack growth were determined for a range of external loads. Using a similar approach except with displacement control instead of load control, it has been investigated whether an engineering threshold value exists below which the crack will grow to a certain length where fiber bridging shields the crack tip sufficiently to cause arrest in crack growth. It was shown that such a threshold value does exist and that crack growth caused by cyclic loading below this threshold comes to an apparent stop.   First A. Author, Second B. Author and Third C. Author    Figure 1: The crack lengths extensions are shown as a function of the number of load cycles for two identical test specimens at different cyclic loads which are pure bending moments at R=0.1. The DCB specimen loaded at the higher bending moment of the two, represented by the dotted marker, clearly shows transient followed by steady state crack growth. The DCB specimen subjected to the lesser load, represented by X’es, also displays transient crack growth, however, it does not reach steady state but rather approaches coming to a halt.    Figure 2: Result of a displacement controlled test showing the max applied load, expressed by the value of the J integral of the applied load, in a load cycle as a function of cycle number. The load initially drops rapidly and levels out as the number of load cycles increases.  As crack growth approaches zero the load approaches what can be considered an engineering threshold for cyclic crack growth.  0 200000 400000 600000 800000 10000000501001502002503003504000501001502002503003504000 200000 400000 600000 800000 1000000Crack extension, a [mm]Number of cycles, N [-]0 200000 400000 600000 800000 1000000010020030040050060070080001002003004005006007008000 10000 20000 30000 40000 50000 60000 70000 80000 90000 100000Applied load, Jext [J/m²]Number of cycles, N [-]

Cyclic crack propagation and - arrest in a unidirectional polymer matrix composite exhibiting large scale bridging

http://orbit.dtu.dk/ws/files/6370464/CRACK%20PROPAGATION.pdf

Cyclic crack propagation and - arrest in a unidirectional polymer matrix composite exhibiting large scale bridging

Abstract

Similar works

Full text

Available Versions

Online Research Database In Technology