Frequently Asked Questions
Some sources are given below, but first a word of warning. Fracture toughness databases are often used to get an estimate of the toughness of materials in an existing structure, from which it is difficult or impossible to extract specimens. It is important to be aware that a fracture toughness database gives only an example of the toughness measured in a given material under particular conditions (such as specimen thickness, heat treatment and test temperature). In isolation, it cannot give an indication of the expected scatter in fracture toughness, which can be very high. Some points to consider are given below:
- Even measurements of toughness reported as KIc measurements, which are therefore considered to be independent of geometry, vary far more than materials parameters such as yield and ultimate tensile strength.
- Ferritic steels, and other materials showing a ductile-brittle transition curve, show very high scatter (a variation in Kmat by an order of magnitude for a single batch of steel has been reported).
- The specification of the material may not be a good guide to its actual toughness. For example, steel sold as BS4360 Grade 50C (now superseded) must meet a Charpy energy requirement of 27J at 0°C. In practice, the steel actually supplied may be considerably better, perhaps meeting the 50E requirement (27J at -40°C). If the toughness of this steel is subsequently treated as 'typical' of Grade 50C and used in a fracture assessment, the estimate of toughness will be optimistic and thus potentially unsafe.
- Most defect assessments require information on weldments, since these are the most likely sites of defects. Few databases specifically address the toughness of weld metal and HAZ, which may be considerably lower than that of the parent material. A careful examination of the weld procedure qualification record is required to determine what tests were actually carried out on the weldments and what the results were. Direct use of the data (if fracture toughness tests were carried out) or estimation of the fracture toughness from Charpy data may then be possible (see FAQon 'What fracture toughness can I assume for a ferritic steel if I know that it meets a certain Charpy energy requirement?')
- If the structure has been in service for a number of years, fracture toughness may be lower than that originally measured, because of in-service embrittlement, e.g. temper embrittlement.
With the above precautions in mind, the following sources may be of use:
- Hudson, CM and Seward, SK: 'A Compendium of sources of fracture toughness and fatigue-crack growth data for metallic alloys, IJF (International Journal of Fracture), vols. 14, R151-R184, 1978, 20, R58-R117, 1982, 39, R43-R63, 1989, 48, R19-R43, 1991
This is a four-part bibliography which gives references to publications containing fracture toughness and fatigue crack growth data; it does not itself contain the data. A wide range of materials is covered, including:
- iron and steel,
- stainless steel,
- titanium, nickel, aluminium, magnesium, copper, zinc, zirconium, molybdenum, cobalt, uranium and tungsten, plus alloys of the above
- 'Structural alloys handbook', published by Battelle Laboratories' Metals and Ceramics Information Center (1985) includes information on fracture toughness of a range of ferrous and non-ferrous alloys. Both the data and their original sources are available in TWI's library (reference only).
- The ASM Metals Handbook series, especially
Volume 1 ('Properties and selection: Irons, steels and high-performance alloys').
Volume 2 ('Properties and selection: Non-ferrous alloys and special-purpose materials').
Volume 3 ('Properties and selection: Stainless steels, tool materials and special-purpose metals').
These references are available from TWI's library (reference only).
- TWI fracture toughness database and reports database; TWI has access to the results of thousands of fracture toughness tests, mainly on welded joints. Selected data can be made available anonymously to TWI Industrial Members on request.
For more information, please contact us.