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:

1. 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.
2. 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 300±10J 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 23°C.

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).