Astm e 561

ASTM-E 399-81 Standard test method Plane-strain fracture toughness of metallic materials... 

Linear elastic fracture mechanics (LEFM) approach can be used to characterize the fracture behavior of random fiber composites. The methods of LEFM should be used with utmost care for obtaining meaningful fracture parameters. The analysis of load displacement records as recommended in method ASTM E 399-71 may be subject to some errors caused by the massive debonding that occurs prior to catastrophic failure of these composites. By using the R-curve concept, the fracture behavior of these materials can be more accurately characterized. The K-equa-tions developed for isotropic materials can be used to calculate stress intensity factor for these materials. 

Figure 15. (a) Variation of plane strain fracture toughness with rubber content for samples with an epoxy-to-polyester ratio of 1 2. Compact tension specimens were tested at 0.2 in./min. using ASTM E-399. (b) Variation of strain-energy release rate, GJc, with rubber content for samples with an epoxy-to-polyester ratio of 1 2. 

The plane strain fracture toughness was determined using ASTM E-399 with compact tension specimens. Specimens were precracked using a razor blade. The ratio of the precrack length to the total length of the sample was kept within the specified limits. Only samples with straight precracks were used for testing, which was done at a rate of 0.2 in./min. 

Standard Method of Test for Plane-Strain Fracture Toughness of Metallic Materials, ASTM E 399-74, 1976 Annual Book of ASTM Standards, Part 10, ASTM, Philadelphia, Pennsylvania (1976), p. 471. 

Standard test methods are used to provide assurance that test data from various laboratories yield meaningful results. Therefore, test specimens must meet the requirements of ASTM E 8 for tensile specimens, ASTM E 23 for Charpy V-notch specimens, and ASTM A 370 for both tensile and Charpy specimens. Fracture toughness specimens and testing methods should meet the intent of ASTM E 399, E 1820 and E 1921. 

Cleavage fracture Quasi-static K c, f Jct produced specimen e.g., ASTM E 399, E 1820, E1921, ESIS... 

Category 2 tests are fracture mechanics tests that use notched and precracked specimens that are statically or dynamically loaded, such as cantilever beam, compact tension, and double cantilever beam specimens, and are conducted per ASTM E 399, Test Method for Plane-Strain Fracture Toughness of Metallic Materials. 

In general, the experimental approach to the problems of crack propagation in non-linear and non-elastic materials is based on the observation and recording of behaviour of specimens with initial notches, and COD measurements were developed by several authors. Later, crack tip opening displacement (CTOD) was determined as a function of crack mouth opening displacement (CMOD) (Velasco et al. 1980), which was directly measured and recorded, for example, according to EN ISO 12737 1999 and ASTM E 399-06 (2006), (cf. Figure 10.5). 

ASTM E 399 90, Standard Test Method for Plane Strain Fracture Toughness of Metallic Mater ials, Annual Book of Standards, Vol. 03.01 (American Society for Testing and Materials, West Conshohocken, Pennsylvania, 2001) pp. 434 464. 

It is ironic that fracture toughness test methods for ceramics, which are bona fide brittle materials, have come so late to the scene. JIS R 1607 arrived in 1990, ASTM C 1421 in 1999, and the ISO and CEN standards in 2003. This is 20 - 33 years after ASTM E 399 was first adopted for metals in 1970. So although ceramists were late, we need not include in our standards the singularly pessimistic statement in E 399 ... 

Category 2 notched and precracked specimens such as cantilever beams, compact tension specimens, and double-cantilever beams (ASTM E 399)... 

The fracture toughness of the laminate material can be measured by a number of methods, some of which are shown in Fig. 4.32. The results will vary with different layup orientations. Other methods may be similar to the test specimens shown in ASTM-E-399 and may involve impact. Presently, the most widely accepted technique for evaluating the fracture toughness of a laminate or structure is a compression test after impact. Compression is a valid indicator without matrix support, the fibers will buckle, while the fibers do not need as much matrix support for tensile loading. 

Almost all standard plane-strain ftacture mechanics test specimens can be adapted to SCC testing. Several examples are illustrated schematically in Fig. 21 (Ref 19). ASTM E 399 describes the allowable specimen dimensions and test procedures for precracked specimens. 

Several designs of initial crack configuration are available. ASTM E 399 recommends that the notch root radius is not greater than 0.127 mm (0.005 in.), unless a chevron notch is used, in which case it can be 0.25 mm (0.01 in.). In order to start out with a crack as sharp as possible, ASTM E 399 describes procedures for precracking. The K level used for precracking should not exceed about two-thirds of the intended initial K value. This procedure prevents the framing of compressive stresses at the crack tip, which may alter the SCC behavior of the alloys. 

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