EN 3873:2010

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Aeronavtika - Preskusne metode za kovinske materiale - Ugotavljanje stopnje rasti razpok, ki nastanejo zaradi utrujenosti, z uporabo preskusnih kosov z razpokami na robovih (CC)Luft- und Raumfahrt - Prüfverfahren für metallische Werkstoffe - Ermittlung der Rißfortschritts- Geschwindigkeit an Cornercrackproben (Eckanris)Série aérospatiale - Méthode d'essais applicables aux matériaux métalliques - Détermination de la vitesse de propagation de fissure en fatigue à l'aide d'éprouvettes avec fissure en coinAerospace series - Test methods for metallic materials - Determination of fatigue crack growth rates using Corner-Cracked (CC) test pieces49.025.05Železove zlitine na splošnoFerrous alloys in generalICS:Ta slovenski standard je istoveten z:EN 3873:2010SIST EN 3873:2011en01-maj-2011SIST EN 3873:2011SLOVENSKI
STANDARD
EUROPEAN STANDARD NORME EUROPÉENNE EUROPÄISCHE NORM
EN 3873
November 2010 ICS 49.025.05; 49.025.15 English Version
Aerospace series - Test methods for metallic materials - Determination of fatigue crack growth rates using Corner-Cracked (CC) test pieces
Série aérospatiale - Méthodes d'essais applicables aux matériaux métalliques - Détermination de la vitesse de propagation de fissure en fatigue à l'aide d'éprouvettes avec fissure en coin
Luft- und Raumfahrt - Prüfverfahren für metallische Werkstoffe - Ermittlung der Rißfortschritts-Geschwindigkeit an Cornercrackproben (Eckanris) This European Standard was approved by CEN on 30 July 2010.
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Information on measuring crack depths in corner-crack test pieces with the direct-current − Potential-drop method . 18Annex B (normative)
Stress-intensity function for corner-crack test pieces
............................................ 22Annex C (normative)
Guidelines on test piece handling and degreasing . 24SIST EN 3873:2011

1) Published by: American Society for Testing and Materials (ASTM), http://www.astm.org/. SIST EN 3873:2011

Effective range of K, due to crack closure-induced reduction applied ∆K (in MPa √m) ∆Kth Fatigue crack growth threshold
The asymptotic value of ∆K for which da/dN approaches zero. For most materials the operational threshold is defined as the ∆K corresponding to 10-7 m/cycle. When reporting ∆Kth, the corresponding lowest decade of near threshold data used in its determination must be given C Normalized K-gradient C = (1/K × dK/da). For load-shedding to attain a desired initial ∆K, C defines the fractional rate of change of K with increasing crack depth a.
C = 1/K × dK/da = 1/Kmax. × dKmax./da = 1/Kmin. × dKmin./da = 1/∆K × d∆K /da, (in mm-1) N Number of loading cycles Stress cycle (fatigue cycle, load cycle) is the smallest segment of the loading waveform spectrum which is repeated periodically N'
Number of stress cycles between two marker cycles Nm Number of stress cycles in a marker cycle ∆N Stress cycle difference r Notch radius (expressed in millimetres) Fm Mean force (expressed in kilonewtons) Fmax. Maximum tensile force applied to the test piece during a cycle (expressed in kilonewtons) Fmin. Minimum tensile force (in kilonewtons) ∆F Force range (in kilonewtons), ∆F = Fmax. − Fmin. q Resolution of crack depth measuring system (expressed in millimetres) R Force ratio (= Fmin./Fmax. = Kmin./Kmax.) R*m Ratio Fmin./Fmax. during a marker cycle Rp 0,2 % offset yield strength (Proof Stress Rp0,2) at test temperature (expressed in megapascals) SIST EN 3873:2011

(3) 4.6 The reference point for measuring the crack depth with CC test pieces is the original corner of the test piece, determined by the projections of the sides of the test piece on the fracture surface adjacent to the notch. Possible rounding of the corner during test piece manufacture will result in this reference point being no longer on the fracture surface. This rounding must be determined to obtain a “Zero-point offset” between the reference point and the rounded corner where the measurement wire is welded, which is used in the calibration of the potential-drop measurements. SIST EN 3873:2011

K = 102aWYF×××π (7) where a is the crack depth (expressed in centimetres); W
is the test piece width (expressed in centimetres); F
is the force (expressed in kilonewtons); K
is the stress-intensity (expressed in MPa√m). A check for this calculation may be made with the following input and results:
a
1 mm (0,1 cm);
W
0,8 cm;
F
32 kN. here Y 0,691; K 19,365. 6.3 Test piece size requirements For the results to be valid, the test pieces are to be subjected to a stress within the elasticity range of the material for all values of the applied load.
If hold times at maximum load are used during CGR testing at elevated temperatures, the initial 0,05 mm to 0,1 mm of growth data may be influenced by such transient effects, and should be considered as suspect, especially if a gradual transition to higher rates is evident after switching to a hold time. NOTE If reduction of the frequency from precracking to test conditions allows Fmax. to increase, due to test machine control characteristics, then all frequency changes, including stops and restarts, should be immediately preceded by a precautionary 10 % reduction in Fmax. and Fmin. to avoid Fmax. overshoot, and later increased. d) The potential at this reference crack depth and Fmin. is recorded and, if precracking was performed at RT the test piece is heated, still at Fmin., to the test temperature, if elevated temperature tests are required. If so, the potential at the test temperature is recorded and used to obtain the temperature correction coefficient
Temp.)(Test (RT)VVYooTC= (10) This coefficient may be used to correct the potentials measured, for use in the crack depth equation (see Annex A). Optimally, the test piece should be precracked at the test temperature. The reference potential is taken at RT in the notched condition, or after heating, to obtain YTC. A different potential-drop calibration will be necessary, however, due to differences between potentials for notches and cracks of the same depths. If the desired R-ratio is higher than 0,1, further cycling must now be performed to reach the desired R-ratio, reducing the loading range by 10 % after each 0,1 mm of crack extension by increasing the minimum load. For materials with Rp ~ 1 000 MPa, and for low R-ratios, reductions may be made after each 0,05 mm of extension, permitting the use of higher initial precracking stress-intensities, or enabling the possibility to reach lower stress-intensities for the initial testing con
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