scholarly journals Model for the Effect of Fiber Bridging on the Fracture Resistance of Reinforced-Carbon-Carbon

2011 ◽  
Vol 133 (2) ◽  
Author(s):  
K. S. Chan ◽  
Y.-D. Lee ◽  
S. J. Hudak
Keyword(s):  
Structural Analysis ◽  
Fracture Resistance ◽  
Structural Integrity ◽  
Crack Opening ◽  
Initiation Toughness ◽  
Resistance Curve ◽  
Opening Displacement ◽  
Fiber Bridging ◽  
3D Composite ◽  
Bridging Law

A micromechanical methodology has been developed for analyzing fiber bridging and resistance-curve behavior in reinforced-carbon-carbon (RCC) panels with a 3D composite architecture and a SiC surface coating. The methodology involves treating fiber bridging traction on the crack surfaces in terms of a weight function approach and a bridging law that relates the bridging stress to the crack opening displacement. A procedure has been developed to deduce material constants in the bridging law from the linear portion of the K-resistance curve. This approach has been applied to analyzing R-curves of RCC generated using double cantilever beam and single cantilever bend specimens to establish a bridging law for RCC. The bridging law has been implemented into a micromechanical code for computing the fracture response of a bridged crack in a structural analysis. The crack geometries considered in the structural analysis include the penetration of a craze crack in SiC into the RCC as a single-edge crack under bending and the deflection of a craze crack in SiC along the SiC/RCC interface as a T-shaped crack under bending. The proposed methodology has been validated by comparing the computed R-curves against experimental measurements. The analyses revealed substantial variations in the bridging stress (σo ranges from 11 kPa to 986 kPa, where σo is the limiting bridging stress) and the R-curve response for RCC due to the varying number of bridging ligaments in individual specimens. Furthermore, the R-curve response is predicted to depend on crack geometry. Thus, the initiation toughness at the onset of crack growth is recommended as a conservative estimate of the fracture resistance in RCC. If this bounding structural integrity analysis gives unacceptably conservative predictions, it would be possible to employ the current fiber bridging model to take credit for extra fracture resistance in the RCC. However, due to the large scatter of the inferred bridging stress in RCC, such an implementation would need to be probabilistically based.

Fracture Resistance of Wire-Wrapped Cylinders

1973 ◽  
Vol 95 (1) ◽  
pp. 219-226 ◽  
Author(s):  
A. K. Shoemaker ◽  
T. Melville ◽  
J. E. Steiner
Keyword(s):  
Yield Strength ◽  
Fracture Resistance ◽  
Crack Extension ◽  
Shear Fracture ◽  
Steel Wire ◽  
Crack Opening ◽  
High Strength ◽  
Opening Displacement ◽  
Propagating Crack ◽  
The Wire

Steel cylinders wrapped with steel wire have the capability of offering not only an economical high-strength structure, but also a structure with improved fracture resistance compared with that of an unwrapped cylinder of equivalent strength. Accordingly, 2000-psi-pressure hydraulic burst tests were therefore conducted to determine the fracture resistance of 36-in-dia, 60-ksi yield-strength, 1000-psi-pressure wire-wrapped cylinders at different levels of shell notch ductility, which was varied by testing at different temperatures. The cylinders were prestressed with 1/4-in-dia cold-drawn wire, and the shells contained part-through-wall flaws. A similarly flawed unwrapped cylinder was tested for comparison. The working-stress level was 72 percent of the specified minimum yield strength in the shell and 60 percent of the minimum tensile strength in the wire. The results showed that at a pressure double that of the unwrapped shell, no crack extension occurred at a temperature at which the steel exhibited fully ductile shell behavior (+110 deg F). A 2-ft crack extension occurred at a temperature (+10 deg F) at which the steel was still in the transition temperature range from ductile-to-brittle behavior (about 20 percent shear fracture), but a brittle crack (−70 deg F) propagated to the end of the wire-wrapped shell. Except for the brittle propagating crack, wire wrapping appears to provide sufficient constraint of a shell defect or propagating crack to limit bulging and crack-opening displacement. A model based on the compatibility in displacements between the crack opening and the local wire strain is presented for calculating the arrest conditions of the propagating crack in the test at 10 deg F. The same flaw size was critical at the constant failure pressure for all test temperatures, and showed that, as predicted, ductile initiation occurs even at the −70 deg F temperature in both the wrapped and unwrapped-cylinder tests. A circumferential flaw was shown to be less critical than a longitudinal flaw of the same size.

In-Situ NDE Monitoring of Crack Bridging in Ceramic Composites via Crack Opening Displacement

1994 ◽  
Author(s):  
Abhisak Chulya ◽  
John P. Gyekenyesi
Keyword(s):  
Crack Opening ◽  
Ceramic Matrix Composites ◽  
Ceramic Composites ◽  
In Situ Observation ◽  
Matrix Composites ◽  
Opening Displacement ◽  
Crack Bridging ◽  
Interferometric Technique ◽  
Fiber Bridging

A study of crack bridging in long-fiber reinforced ceramic matrix composites (CMC) is the main focus of this paper. The in-situ observation using NDE techniques reveals that 1D SiC/CAS CMCs show only partial fiber bridging behavior while 2D SiC/SiC CMCs possess an excellent bridging mechanism. Laser interferometric technique was successfully applied to measure crack opening displacements (COD) in the notched specimens under four-point flexural loading. The onset of precracking and the effects of fiber bridging were also detected by in-situ optical microscopy and acoustic emission techniques. The applied load-COD relations were shown and on the basis of these results, the bridging stiffness parameter can be determined via the fracture mechanics formulation proposed by Cox and Marshall.

Comparative Evaluation of Fracture Mechanics Methodologies as Applied to Offshore Structural Design and Integrity Analyses

1985 ◽  
Vol 107 (4) ◽  
pp. 479-484
Author(s):  
H. C. Rhee ◽  
M. M. Salama
Keyword(s):  
Fracture Mechanics ◽  
Structural Design ◽  
Crack Opening ◽  
Resistance Curve ◽  
Opening Displacement ◽  
Design Curve ◽  
Strain Relationship ◽  
Curve Method ◽  
Offshore Industry ◽  
Material Fracture

A comparative study was performed to evaluate the three most widely used elastic-plastic fracture mechanics methodologies. The three methods are the crack opening displacement (COD) design curve, which is widely used in the offshore industry, the British Central Electricity Generating Board (CEGB) R6 method, and the J-resistance curve method. Analyses of various flawed geometries based on these three methods were performed using consistent material fracture properties. The results of both the COD and R6 methods were compared with those of the J-resistance curve, which is the most rigorous of the three methods. The results of the COD concept, following BSI PD 6493 procedures, appear to be conservative at applied stress levels below 60 percent of the material yield strength and unconservative above this value. However, the results of the R6 method appear to be consistently conservative. The behavior of COD design curve solutions can be improved when the structural geometry and the actual stress-strain relationship are properly considered in the analyses.

A Method of J Testing Based on Crack Opening Displacement for Circumferential Through-Wall Cracked Pipes under Combined Tension and Bending

2006 ◽  
Vol 110 ◽  
pp. 63-70
Author(s):  
Nam Su Huh ◽  
Ludwig Stumpfrock ◽  
Eberhard Roos ◽  
Yun Jae Kim ◽  
Young Jin Kim
Keyword(s):  
Crack Opening Displacement ◽  
Conventional Method ◽  
Crack Opening ◽  
Estimation Method ◽  
Combined Loading ◽  
Resistance Curve ◽  
Opening Displacement ◽  
Load Line ◽  
Load Line Displacement ◽  
Leak Before Break

Application of the leak-before-break concept to nuclear piping requires accurate fracture mechanics assessment on pipes with postulated circumferential through-wall crack subject to combined tension and bending. One important element is determination of relevant J-resistance curve for pipes under combined loading. This paper provides experimental J estimation method for the circumferential through-wall cracked pipe under combined tension and bending, based on the load-crack opening displacement (COD) record to estimate J-resistance curve. To give confidence in the proposed method, the J results from detailed elastic-plastic finite element (FE) analysis are also compared with estimated J based not only on proposed method but also on conventional method using load-load line displacement, which shows that estimated J based on the proposed method provides reliable J estimates regardless of analysis condition, on the other hand, the conventional method using the load-load line displacement record gives erroneous results for shallow cracks.

Estimation Procedures for J and CTOD Fracture Parameters Experimental Evaluation Using Homogeneous and Mismatched Pin-Loaded SE(T) Specimens

2010 ◽  
Author(s):  
Gabriel P. de Oliveira ◽  
Gustavo H. B. Donato
Keyword(s):  
Experimental Evaluation ◽  
Fracture Resistance ◽  
Structural Integrity ◽  
Mouth Opening ◽  
Pressure Vessels ◽  
Weld Strength ◽  
Crack Mouth Opening Displacement ◽  
J Integral ◽  
Opening Displacement ◽  
Conceptual Background

Experimental evaluation of geometry-dependent material’s fracture resistance using constraint-designed SE(T) specimens has proved to be an accurate option to assess the structural integrity of pipelines and pressure vessels reducing excessive conservatism. In this context, this work presents procedures for experimental J-integral and CTOD (δ) evaluation using the eta (η) method applied to tension pin-loaded SE(T) specimens made of homogeneous materials and also containing mismatched joints. Initially, the conceptual background is presented, followed by the description of the refined non-linear finite element models developed, which provide the necessary evolution of load with increased load-line and crack mouth opening displacement. As results, are presented η factors for J-integral estimation and CTOD calculations, which are not available in current standardized procedures. The main objective is to allow fracture resistance experimental evaluation using specimens of different a/W-ratios, material flow properties, weld joint configurations and levels of weld strength mismatch. The main motivation is the possibility of enhancing accuracy of pressure vessels and piping integrity assessments, since these later present very close fracture conditions if compared to SE(T) specimens. The present results, when taken together with previous developments, extend the knowledge about the use of pin-loaded SE(T) specimens. The reader should enhance the studies about the topic with the complimentary paper with the same title beginning but involving clamped SE(T) specimens.

scholarly journals Μελέτη θραυστότητας δομικών λίθων ιστορικών μνημείων και αποτίμηση των αποτελεσμάτων υλικών στερέωσης

2018 ◽  
Author(s):  
Νικόλαος-Στυλιανός Χανακούλας
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Structural Analysis ◽  
Intensity Factor ◽  
Crack Opening Displacement ◽  
Critical Stress ◽  
Crack Opening ◽  
Critical Stress Intensity Factor ◽  
Analysis Program ◽  
Opening Displacement

Αντικείμενο της παρούσας έρευνας είναι η μελέτη θραυστότητας δομικών λίθων ιστορικών μνημείων, καθώς και η αποτίμηση υλικών στερέωσης. Ως εκ του τούτου, η έρευνα χωρίζεται σε δύο μέρη. Στο πρώτο μέρος πραγματοποιείται η μελέτη θραυστότητας δομικών λίθων. Για το σκοπό αυτό χρησιμοποιήθηκαν τέσσερις τύποι λίθων. Πιο συγκεκριμένα μάρμαρο και ασβεστόλιθος Μάνης, ο οποίος συναντάται σε διάφορα ιστορικά κτίρια όπως το Αρχοντικό των Μεδίκων και το Δημοτικό Κτίριο Οιτύλου, ψαμμιτικός ασβεστόλιθος Λευκωσίας από την Κύπρο, ο οποίος συναντάται σε ιστορικά κτίρια όπως η Δημοτική Αγορά Λεμεσού και τέλος πωρόλιθος Λευκωσίας από την Κύπρο, που συναντάται σε ιστορικά κτίρια όπως η ενορία της Χρυσαλινιώτισσας. Η αντοχή σε θραύση των δειγμάτων μαρμάρου και ασβεστόλιθου Μάνης υπολογίστηκε με τη διεξαγωγή πειραμάτων κάμψης τριών σημείων σε δείγματα με προϋπάρχουσες ρωγμές. Τα δείγματα αυτά ήταν πρισματικοί δοκοί, με εγκοπές στο κέντρο διαφόρων βαθών (σχήμα εγκοπής U). Για την μελέτη λήφθηκαν υπόψη το άνοιγμα της εγκοπής ή αλλιώς Crack Opening Displacement (COD), καθώς και ο Κρίσιμος Συντελεστής Εντάσεως των Τάσεων ή αλλιώς Critical Stress Intensity Factor (KIC) για τον Τρόπο Ι. Η έρευνα αποκάλυψε ότι η αντοχή σε θραύση παραμένει σταθερή όταν η αναλογία της εγκοπής σε σχέση με το ύψος του δείγματος υπερβαίνει το 0,2. Κατόπιν πραγματοποιήθηκαν δοκιμές θραύσης κατά τον ίδιο ακριβώς τρόπο στον ψαμμιτικό ασβεστόλιθο και πωρόλιθο Λευκωσίας, με μόνη διαφορά τις διαστάσεις στις εγκοπές, όπου είχαν το ίδιο πλάτος με το ύψος της ρωγμής. Η έρευνα αποκάλυψε ότι η αντοχή σε θραύση παραμένει η ίδια, πράγμα που υποδεικνύει ότι η αντοχή σε θραύση εξαρτάται κυρίως από το ύψος της εγκοπής και όχι τόσο από το πάχος της.Στα πλαίσια της παρούσας περιεκτικής μεθοδολογίας για την προσέγγιση των ιστορικών κτιρίων, στο δεύτερο και τελικό στάδιο της έρευνας πραγματοποιήθηκε μελέτη στο ιστορικό κτίριο «Αρχοντικό των Μεδίκων» της Μάνης, όπου έγινε περιγραφή του με μοντέλο πεπερασμένων στοιχείων. Για την περιγραφή πραγματοποιήθηκαν κάποιες επιπλέον δοκιμές στα δείγματα του πρώτου μέρος και πιο συγκεκριμένα αντοχής σε θλίψη για τον ασβεστόλιθο Μάνης αλλά και εφελκυσμού στο κονίαμα του κτιρίου. Στη συνέχεια έγινε έλεγχος της στατικής συμπεριφοράς του μοντέλου υπό την επίδραση σεισμικών δράσεων στην υπάρχουσα κατάστασή του αλλά και αποτιμώντας το με τρεις διαφορετικές προτάσεις αποκατάστασης με υλικά στερέωσης από ανόργανα υλικά (HAP) και αλκοξυσιλάνια (ES και TEOS), πάντα με τη βοήθεια του λογισμικού προγράμματος SAP2000 v18.2. 0 - Structural Analysis Program.

Review of Low-Constraint Fracture Resistance Testing With SENT Specimens

2014 ◽  
Author(s):  
Xian-Kui Zhu ◽  
Tom McGaughy ◽  
Fabian Orth ◽  
Jon Jennings
Keyword(s):  
Fracture Resistance ◽  
Crack Tip ◽  
Test Methods ◽  
Resistance Testing ◽  
Resistance Curve ◽  
Single Specimen ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Resistance Curves ◽  
Low Constraint

Fracture resistance is an important material property and characterized by a J-integral resistance curve (J-R curve) or a crack-tip opening displacement (CTOD) resistance curve. ASTM standard specimens with deep cracks are subject to bending dominant forces, leading to high crack-tip constraint conditions and conservative fracture resistance curves. Actual cracks occurring in line pipes and welds are often shallow ones dominated by tensile forces, resulting in low constraint conditions. Shallow cracks have been shown to generate elevated fracture resistance curves in comparison to standard deep-crack results. To reduce the over-conservatism of standard resistance curves and to produce more realistic toughness properties to meet the needs of strain-based design approaches for pipelines, different procedures and technologies have been developed over the years to determine the low-constraint fracture resistance curves by use of the single edge-notched tension (SENT) specimens. This includes the multiple specimen method developed and standardized by DNV for J-R curve testing, the single specimen method developed by CanMet for J-R and CTOD-R curve testing, and the single-specimen method developed by ExxonMobil for CTOD-R curve testing. This paper delivers a technical review of existing fracture test methods using SENT specimens, and discusses the advantages and limitations of each method.

Rationalizing Sampling of Pipe Material Properties for Probabilistic Pipe Fracture Analyses

2016 ◽  
Author(s):  
Richard Olson ◽  
Bruce Young
Keyword(s):  
Material Properties ◽  
Crack Opening ◽  
Strain Curve ◽  
Initiation Toughness ◽  
Pipe Material ◽  
Stress Strain Curve ◽  
Opening Displacement ◽  
Time Step ◽  
Stress Strain ◽  
Suggested Approach

One element of probabilistic pipe fracture analyses is an assessment of the stability of cracks under applied load. If the load at some time step is greater than the cracked section can sustain, the state of the pipe is reported as ruptured. Another element of probabilistic pipe fracture analyses is the calculation of the crack opening displacement (COD) value which is used as an input to a leak rate calculation. Both of these analyses typically require pipe material properties that are sampled from a probabilistic distribution characterized by a mean value and some variance about the mean. Such properties include yield strength, ultimate strength, Ramberg-Osgood stress-strain curve coefficients, and fracture toughness curve parameters such as initiation toughness and tearing parameters. From a procedural perspective, it is tempting to sample all of the relevant parameters independently. However, in some instances, the assumption of independence leads to nonsensical conditions such as yield being greater than ultimate; yield and ultimate being completely disconnected from the underlying Ramberg-Osgood description of the stress-strain curve; J-R toughness curves that are convex instead of concave; or initiation J values as low as zero. This paper provides a suggested approach to sampling material properties for probabilistic pipe fracture analyses. The approach maintains consistency between yield, ultimate and the underlying Ramberg-Osgood stress-strain curve, and sets reasonable cutoff limits on the properties that are sampled. Equations for ensuring consistency among the related parameters are given along with justifications for the sampling limits, and an example of application of the proposed methodology.

Crack Opening for Steam Generator Tubes With Realistic Boundary Conditions

2016 ◽  
Author(s):  
Wolf Reinhardt ◽  
Revi Kizhatil
Keyword(s):  
Steam Generator ◽  
Structural Integrity ◽  
Crack Opening ◽  
Leakage Rate ◽  
High Ductility ◽  
Tube Material ◽  
Opening Displacement ◽  
Initiation Mechanism ◽  
Steam Generator Tubes ◽  
Leak Before Break

Steam generator tubes are subject to operational loads in the presence of aggressive environmental conditions. This combination of conditions can sometimes result in through-wall cracks. Since the tube material has high ductility, detectable leaks may occur long before the structural integrity of the tubes is challenged. Although operation with confirmed cracks is typically not permitted, the presence of cracks cannot be ruled out when an initiation mechanism is active. There are two scenarios dealing with through-wall cracks, namely leak-before-break that deals with the integrity of through-wall cracks with leakage below the operational shutdown limit, and an accident pop-through scenario where an accident overload causes a part-through-wall crack to penetrate the wall and leak. Both leak-before break and accident pop-through scenarios involve the calculation of leakage rate through the crack, which in turn needs the opening of the crack under the applied loads to be determined. The opening displacement is affected by the size of the crack and by the stiffness of the tube with its supports. Ignoring the effect of the tube on crack opening can severely overestimate the crack opening. The present paper discusses a method to include the tube stiffness in calculating crack opening with the objective of determining leakage. The method addresses both elastic and plastic conditions at the crack and in the surrounding tube.

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