Fracture Toughness Testing for Improving the Safety of Gas Pipelines

2016 ◽  
Vol 821 ◽  
pp. 464-470
Author(s):  
Ľubomír Gajdoš ◽  
Martin Šperl
Keyword(s):  
Mechanical Properties ◽  
Fracture Toughness ◽  
Fracture Mechanics ◽  
Mechanical Tests ◽  
Internal Stresses ◽  
Pipe Material ◽  
Cylindrical Wall ◽  
Fracture Toughness Testing ◽  
Toughness Testing ◽  
Thin Walled

For standard fracture mechanical tests flat specimens (principally CT or SENB) are required. When investigating fracture mechanical properties of thin – walled pipes this brings about a problem because it is necessary to straighten pipe bands. However, this operation causes internal stresses to be induced not only in the semi-product subjected to straightening but also in finished specimens. A question therefore arises to what extent are then the magnitudes of the fracture toughness determined representative for the actual cylindrical wall. To solve this problem fracture mechanics tests were caried out on flat (straightened) CT specimens as well as on curved CT specimens with the natural curvature. The R – curves as well as the resulting parameters of the fracture toughness, obtained for both types of CT specimens, were compared and it was concluded that the fracture toughness of the pipe material determined on straightened CT specimens was practically the same as that obtained on curved CT specimens.

Fracture Toughness Testing and its Implications to Engineering Fracture Mechanics Analysis of Energy Pipelines

2018 ◽  
Author(s):  
Sergio Limon ◽  
Peter Martin ◽  
Mike Barnum ◽  
Robert Pilarczyk
Keyword(s):  
Fracture Toughness ◽  
Fracture Mechanics ◽  
Test Data ◽  
Fracture Mode ◽  
Fracture Process ◽  
Fracture Behavior ◽  
Fracture Initiation ◽  
Fracture Toughness Testing ◽  
Final Fracture ◽  
Toughness Testing

The fracture process of energy pipelines can be described in terms of fracture initiation, stable fracture propagation and final fracture or fracture arrest. Each of these stages, and the final fracture mode (leak or rupture), are directly impacted by the tendency towards brittle or ductile behavior that line pipe steels have the capacity to exhibit. Vintage and modern low carbon steels, such as those used to manufacture energy pipelines, exhibit a temperature-dependent transition from ductile-to-brittle behavior that affects the fracture behavior. There are numerous definitions of fracture toughness in common usage, depending on the stage of the fracture process and the behavior or fracture mode being evaluated. The most commonly used definitions in engineering fracture analysis of pipelines with cracks or long-seam weld defects are related to fracture initiation, stable propagation or final fracture. When choosing fracture toughness test data for use in engineering Fracture Mechanics-based assessments of energy pipelines, it is important to identify the stage of the fracture process and the expected fracture behavior in order to appropriately select test data that represent equivalent conditions. A mismatch between the physical fracture event being modeled and the chosen experimental fracture toughness data can result in unreliable predictions or overly conservative results. This paper presents a description of the physical fracture process, behavior and failure modes that pipelines commonly exhibit as they relate to fracture toughness testing, and their implications when evaluating cracks and cracks-like features in pipelines. Because pipeline operators, and practitioners of engineering Fracture Mechanics analyses, are often faced with the challenge of only having Charpy fracture toughness available, this paper also presents a review of the various correlations of Charpy toughness data to fracture toughness data expressed in terms of KIC or JIC. Considerations with the selection of an appropriate correlation for determining the failure pressure of pipelines in the presence of cracks and long-seam weld anomalies will be discussed.

Si3N4/BN Composite Ceramics with Nd2O3-Al2O3-Y2O3 Ternary Additives by Pressureless Sintering

2010 ◽  
Vol 434-435 ◽  
pp. 106-108
Author(s):  
Ping Liu ◽  
Yong Feng Li ◽  
Xiang Dong Wang ◽  
Hai Yun Jin ◽  
Guan Jun Qiao
Keyword(s):  
Mechanical Properties ◽  
Fracture Toughness ◽  
Phase Transformation ◽  
Flexural Strength ◽  
Pressureless Sintering ◽  
Sintering Process ◽  
Composite Ceramics ◽  
Fracture Toughness Testing ◽  
Β Phase ◽  
Toughness Testing

Si3N4/BN composite ceramics with 25vol% h-BN were prepared by pressure-less sintering process with Nd2O3/Al2O3/Y2O3 as sintering additives. The effects of these ternary additives on the densification behaviors and mechanical properties were investigated. XRD and FESEM were used to investigate the α-β phase transformation and microstructure. The XRD results showed that α-Si3N4 has transformed to β-Si3N4 completely in all the samples during the pressureless sintering process. The line shrinkage increased with the Nd2O3 contents increasing, and the highest line shrinkage (7.75%) was observed when 4wt% Nd2O3 was added, then decreased. The same trends were observed in flexural strength and fracture toughness testing. The ternary additives of Y2O3-Al2O3-Nd2O3 could improve the density, strength and fracture toughness of the material effectively.

Mechanical Properties of Toughened Polyester Reinforced with Untreated and Treated Kenaf Hybird Carbon Composite

2017 ◽  
Vol 894 ◽  
pp. 17-20
Author(s):  
Noor Najmi Bonnia ◽  
Aein Afina Redzuan ◽  
Siti Norasmah Surip ◽  
Noor Azlina Hassan
Keyword(s):  
Mechanical Properties ◽  
Fracture Toughness ◽  
Impact Strength ◽  
Carbon Black ◽  
Hybrid Composites ◽  
Carbon Composite ◽  
Compression Moulding ◽  
Fracture Toughness Testing ◽  
Rubber Toughened ◽  
Toughness Testing

This research focusing on mechanical properties of rubber toughened polyester filled carbon black (RPCB) reinforced with untreated kenaf (RPCBUK) and treated kenaf (RPCBTK). The samples were fabricated via compression moulding technique in which 3 % of LNR was added as toughening agent in this composite. Percentages of carbon black (CB) is 4 % and kenaf used vary from 5,10,15,20 and 25wt %. The mechanical properties were evaluated by impact and fracture toughness testing. The result for each test was discussed to determine the most optimum loading of kenaf fibre used to produce the best properties of composite. Untreated hybrid composite showed improvement on impact strength as compared to RPCB composite. RPCBTK with 25% of kenaf and RPCBUK with 5% of kenaf loading give the highest impact strength among the hybrid composites, approaching the strength of neat polyester. Same trend shows by fracture toughness testing. The microstructures of the composites’ fracture surface images from scanning electron microscope (SEM) prove the mechanical properties of the hybrid composites.

Development of Fracture Toughness Testing of Thin-Width SEN(B) Specimens

2011 ◽  
Author(s):  
R. S. Kulka
Keyword(s):  
Fracture Toughness ◽  
Fracture Mechanics ◽  
Test Specimen ◽  
Stress Triaxiality ◽  
Crack Tip ◽  
Element Analysis ◽  
Fracture Toughness Testing ◽  
Out Of Plane ◽  
Toughness Testing ◽  
Crack Tip Constraint

During fracture toughness testing of SEN(B) specimens, an important assumption is that the test specimen is highly constrained. This assumption is ensured by the testing of a deeply cracked specimen, with in-plane and out-of-plane dimensions that are sufficient to guarantee an appropriate level of crack tip stress triaxiality. This condition guarantees that high-constraint fracture toughness values are derived, conservative for use in standard fracture mechanics assessments. In reality, many components have small in-plane or out-of-plane dimensions. It is considered that this could cause a reduction in crack tip constraint of a sufficient amount to increase the effective fracture toughness of the components. However, there is currently limited understanding as to the magnitude of the benefits that could be claimed. Finite element analysis of various thin-width SEN(B) specimens has been undertaken. The knowledge gained can be used to develop fracture mechanics methodology for the testing of thin-width specimens and the subsequent derivation of appropriate toughness values.

Equipment for fracture toughness testing of specimen at low temperatures

1988 ◽  
Vol 20 (5) ◽  
pp. 698-702
Author(s):  
I. D. Abushenkov ◽  
A. I. Alekseev ◽  
V. Ya. Il'ichev ◽  
N. I. Mokryi ◽  
A. I. Telegon ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Low Temperatures ◽  
Fracture Toughness Testing ◽  
Toughness Testing
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