Charpy Impact Test for Metallic Materials

Charpy Impact Test for Metallic Materials

Charpy impact test method for metallic materials is specified by European EN 10045 standard. This specification defines terms, dimension and tolerances of test pieces, type of the notch (U or V), test force, verification of impact testing machines etc.

For certain particular metallic materials and applications, Charpy impact test may be the subject of specific standards and particular requirements. The test consists of breaking by one blow from a swinging pendulum, under conditions defined by standard, a test piece notched in the middle and supported at each end. The energy absorbed is determined in joules. This absorbed energy is a measure of the impact strength of the material.

The designations applicable to this standard are as indicated in the Table 1 and on the Figure1.

Table 1. Characteristics of test piece and testing machine

Reference (Figure 1) Designation Unit

1 Length of test piece mm

2 Height of test piece mm

3 Width of test piece mm

4 Height below notch mm

5 Angle of notch Degree

6 Radius of curvature of base of notch mm

7 Distance between anvils mm

8 Radius of anvils mm

9 Angle of taper of each anvil Degree

10 Angle of taper of striker Degree

11 Radius of curvature of striker mm

12 Width of striker mm

- Energy absorbed by breakage KU or KV Joule

Figure 1. Charpy impact test

Test pieces

The standard test piece shall be 55 mm long and of square section with 10 mm sides. In the centre of the length, there shall be a notch. Two types of notch are specified:

a. V notch of 45, 2 mm deep with a 0,25 mm radius of curve at the base of notch. If standard test piece cannot be obtained from the material, a reduced section with a width of 7,5 mm or 5 mm shall be used, the notch being cut in one of the narrow faces.

b. U notch or keyhole notch, 5 mm deep, with 1 mm radius of curve at the base of notch. The test pieces shall be machined all over, except in the case of precision cast foundry test pieces in which the two faces parallel to the plane of symmetry of the notch can be unmachined.

The plane of symmetry of the notch shall be perpendicular to the longitudinal axis of the test piece.

The tolerances of the specified dimensions of the test piece are given by standard as well. For the standard test piece, machining tolerance in length is 0.6 mm for both type of tests, and tolerances in height are 0.11 mm for U and 0.06 mm for V notch test piece. Tolerances for angle between plane of symmetry of the notch and longitudinal axis of test piece as well as for angle between adjacent longitudinal faces of test piece are 2 only.

Comparison of results is only of significance when made between test pieces of the same form and dimensions. Machining shall be carried out in such a way that any alternation of the test piece, for example due to cold working or heating, is minimized. The notch shall be carefully prepared so that no grooves, parallel to the base of the notch, are visible to the naked eye. The test piece may be marked on any face not in contact with the supports or anvils and at a point at least 5 mm from the notch to avoid the effects of cold working due to marking.

Testing machine

The testing machine shall be constructed and installed rigidly and shall be in accordance with European Standard 10 045 part 2.

Standard test condition shall correspond to nominal machine energy of 30010J at the use of a test piece of standard dimensions. The reported absorbed energy under these conditions shall be designated by the following symbols:

KU for a U notch test piece

KV for a V notch test piece

Testing machines with different striking energies are permitted, in which case the symbol KU or KV shall be supplemented by an index denoting the energy of the testing machine.

For example KV 150 denotes available energy of 150 J, and KU 100 denotes available energy of 100 J. KU 100 = 65 J means that:

nominal energy is100 J

standard U notch test piece is used

energy absorbed during fracture is 65 J.

For tests on a subsidiary V notch test piece, the KV symbol shall be supplemented by indices denoting first the available energy of the testing machine and second the width of the test piece, e.g.:

KV 300 / 7,5: available energy 300 J, width of test piece 7.5 mm

KV 150 / 5: available energy 150 J, width of test piece 5 mm

KV 150 / 7,5 = 83 J denotes:

nominal energy 150 J

reduced section test piece of width 7,5 mm

energy absorbed during fracture: 83 J.

The test piece shall lie against the anvils in such a way that the plane of symmetry of the notch shall be no more than 0.5 mm from the plane of symmetry of the anvils. If the test temperature is not specified in the product standard, it shall be about 23C.

National standards corresponding to EN 10045-2 are DIN 51306 (1983), NFA 03-508 (1985), BS 131 Part 4 (1972) and international ISO 442 (1965).

Charpy impact test

An Impact test machine.

The Charpy impact test is a standardized high strain-rate test which determines the amount of energy absorbed by a material during fracture. This absorbed energy is a measure of a given material's toughness and acts as a tool to study brittle-ductile transition. It is widely applied in industry, since it is easy to prepare and conduct and results can be obtained quickly and cheaply. But a major disadvantage is that all results are only comparative.[1]The qualitative results of the fracture may be used to determine the toughness of the material. Also, this test may be done with the material at various temperatures to determine the brittle-ductile transition temperature.

DefinitionThe apparatus consists of a pendulum hammer swinging at a notched sample of material. The energy transferred to the material can be inferred by comparing the difference in the height of the hammer before and after a big fracture.

The notch in the sample affects the results of the impact test,[2] thus it is necessary for the notch to be of a regular dimensions and geometry. The size of the sample can also affect results, since the dimensions determine whether or not the material is in plane strain. This difference can greatly affect conclusions made.[3]Quantitative resultsThe quantitative result of the impact testthe energy needed to fracture a materialcan be used to measure the toughness of the material and the yield strength. Also, the strain rate may be studied and analyzed for its effect on fracture.

The ductile-brittle transition temperature (DBTT) may be derived from the temperature where the energy needed to fracture the material drastically changes. However, in practice there is no sharp transition and so it is difficult to obtain a precise transition temperature. An exact DBTT may be empirically derived in many ways: a specific absorbed energy, change in aspect of fracture (such as 50% of the area is cleavage), etc.[1] Qualitative resultsThe qualitative results of the impact test can be used to determine the ductility of a material.[4] If the material breaks on a flat plane, the fracture was brittle, and if the material breaks with jagged edges or shear lips, then the fracture was ductile. Usually a material does not break in just one way or the other, and thus comparing the jagged to flat surface areas of the fracture will give an estimate of the percentage of ductile and brittle fracture.[1]Sample sizesAccording to ASTM A370, standard specimen for Charpy impact test is 10mm10mm55mm. Subsize specimen are: 10mm7.5mm55mm , 10mm6.7mm55mm , 10mm5mm55mm , 10mm5mm55mm , 10mm3.3mm55mm , 10mm2.5mm55mm. Details of specimen as per ASTM A370 (Standard Test Method and Definitions for Mechanical Testing of Steel Products).

Notes1. ^ a b c Meyers and Chawla. Mechanical Behaviors of Materials. Prentice Hall, Inc. (Pearson Education). (1999).

2. ^ Kurishita, H et al. Effects of V-Notch Dimensions on Charpy Impact Test Results for Differently Sized Miniature Specimens of Ferritic Steel. Materials Transactions, JIM (Japan). 34, No. 11, 10421052 (1993).

3. ^ Mills, N. J. The mechanism of brittle fracture in notched impact tests on polycarbonate. J. of Mater. Sci., 11, No. 2, 363375 (1976)

4. ^ Mathurt, KK et al. 3D analysis of failure modes in the Charpy impact test. Modeling Simul. Mater. Sci. Eng., 2, 617635 (1994).

See also Izod impact strength test

Ductility

Brittle

Impact force

Size Effects in the Charpy V-Notch TestJournalInternational Journal of Fracture

PublisherSpringer Netherlands

ISSN0376-9429 (Print) 1573-2673 (Online)

IssueVolume 116, Number 3 / August, 2002

DOI10.1023/A:1020112028641

Pages275-296

Subject CollectionChemistry and Materials Science

SpringerLink DateTuesday, November 02, 2004

A.A.Benzerga1, V.Tvergaard2 and A.Needleman3

AbstractIssues related to the size dependence of the upper shelf energy (USE) and the ductile-to-brittle transition temperature (DBTT) in the Charpy V-notch test are investigated. Emphasis is placed on the interplay between inertial, strain rate hardening, strain hardening, thermal softening and material length scale effects. Geometrically similar specimens are considered first. For such specimens, the ductile-to-brittle transition temperature is found to increase with specimen size, with the amount of the increase depending on the material properties. To model available experiments, calculations are also carried out for Charpy specimens where only the ligament size is varied and two classes of pipe steels are considered. For a relatively high strength pipe steel, the experimental results exhibit no size dependence of the DBTT. On the other hand, a significant shift in the DBTT is obtained for a low strength steel. The numerical studies are used to understand the difference between these two classes of steels. The extent to which the size effect is material dependent is investigated.

Impact loading-high strain-rate-adiabatic heating-ductile-brittle transition