ISO 148-2:2016 download.Me(allic materials — Charpy pendulum impact test — Part 2: Verification of testing machines.
Introduction
The suitability of a pendulum impact testing machine for acceptance testing of metallic materials has usually been based on a calibration of its scale and verification of compliance with specified dimensions, such as the shape and spacing of the anvils supporting the specimen. The scale calibration is commonly verified by measuring the mass of the pendulum and its elevation at various scale readings. This procedure for evaluation of machines had the distinct advantage of requiring only measurements of quantities that could be traced to national standards. The objective nature of these traceable measurements minimized the necessity for arbitration regarding the suitability of the machines for material acceptance tests.
However, sometimes two machines that had been evaluated by the direct-verification procedures described above, and which met all dimensional requirements, were found to give significantly different impact values when testing test pieces of the same material.
This difference was commercially important when values obtained using one machine met the material specification, while the values obtained using the other machine did not. To avoid such disagreements, some purchasers of materials added the requirement that all pendulum impact testing machines used for acceptance testing of material sold to them are to be indirectly verified by testing reference test pieces supplied by them. A machine was considered acceptable only if the values obtained using the machine agreed, within specified limits, with the value furnished with the reference test pieces.
This part of ISO 148 describes both the original direct verification and the indirect verification procedures.
1 Scope
This part of ISO 148 covers the verification of pendulum-type impact testing machines, in terms of their constructional elements, their overall performance and the accuracy of the results they produce. It is applicable to machines with 2 mm or 8 mm strikers used for pendulum impact tests carried out, for instance, in accordance with ISO 148-I.
IL can be applied to pendulum Impact esung machines of various capacities and oldilTerent design.
Impact machines used for industrial, general or research laboratory testing of metallic materials in accordance with this part of ISO 148 are referred to as industrial machines. Those with more stringent requirements are referred to as reference machines. Specifications for the verification of reference machines are found in ISO 148-3.
This part oF ISO 148 describes two methods of verification.
a) The direct method, which is static In nature, Involves measurement of the critical parts of the machine to ensure that It meets the requirements of this part of ISO 148. Instruments used for the verification and calibration are traceable to national or international standards.
b) The indirect method. which is dynamic in nature, uses reference test pieces to verify points on the measuring scale for absorbed energy. The requirements for the reference test pieces are found in
ISO 148-3.
A pendulum impact testing machine is not in compliance with this part of ISO 148 untIl It has been verified by both the direct and Indirect methods and meets the requirements of Clause 6 and Clause 7.
This part of ISO 148 describes how to assess the different components of the total energy absorbed in fracturing a test piece This total absorbed energy consists of
— the energy needed to fracture the test piece itself, and
— the Internal energy losses of the pendulum impact testing machine performing the first half-cycle swing from the Initial position.
NOTE Internal energy losses are due to the following:
— air resistance, Iricuon of the bean ags of the rotation axis and olthe Indicating pointer of the pendulum which can be determined by the direct method (see 6.4.5);
— shock of the foundation, vibration olthe frame and pendulum for whIch no suitable measuring methods and apparatus have been developed.
2 Nonnatlve references
The following documents, in whole or In part are normatively referenced in this document and are indispensable for Its application. For dated references, only the edition cited applies. For undated references, the latest edition olthe referenced document (including any amendments) applies.
ISO 148-1. Met allic materials — Charpy pendulum impart test — Part 1: Test method
b) Ensuring that the machine is not subject to external vibrations transmitted through the foundation at the time of the impact test.
NOTE This can be accomplished, for example, by placing a small container of water on any convenient location on the machine fi-amework. The absence of ripples on the water surface during an impact test indicates that this requirement has been met.
6.3 Machine framework
6.3.1 Inspection of the machine framework (see Figure 1) shall consist of determining the following items
a) free position of the pendulum;
b) location of the pendulum In relation to the supports;
c) transverse and radial play of the pendulum bearings;
d) clearance between the hammer and the framework.
Machines manufactured after 1998 shall have a reference plane from which measurements can be made. Annex C Is provided for In formation.
6.3.2 The axis of rotation of the pendulum shall be parallel to the reference pLane to within 2/1 000. This shall be certified by the manufacturer.
6.3.3 The machine shall be installed so that the reference plane is honzontal to within 2/1 000.
For pendulum mpact testing machines without a reference plane, the axis of rotation shall be established to be horizontal to within 4/1 000 directly or a reference plane shall be established from which the horizontality of the axis of rotation can be verified as described above.
6.3.4 When hanging free, the pendulum shall hang so that the striking edge is within 2,5 mm of the position where IL would lust touch the test specimen.
NOTE This condition can be determined using a gauge In the form of a bar that Is approxImately 55 mm In length and of rectangular section 7,5mm by 12.5mm (see Flgurc3.).
6.3.5 The plane of swing of the pendulum shall be 90,00 ± O,1 to the axis of rotation (U c 0,05),
6.3.6 The striker shall make contact over the full thickness of the test piece.
One method of verifying this Is to use a test piece having dimensions of 55 mm a 10 mm a 10 mm that Is tightly wrapped in thin paper (e.g. by means of adhesive tape) and a striking edge that is tightly wrapped In carbon paper with the carbon side outermost (i.e. not facing the striker). From its position of equilibrium, the pendulum is raised a few degrees, released so that it contacts the test piece, and prevented from contacting the test piece a second time. The mark made by the carbon paper on the paper covering the test piece should extend completely across the paper. This verification can be performed concurrently with that of checking the angle of contact between the striker and the test piece (see 6AU).
6.3.7 The pendulum shall be located so that the centre of the striker and the centre of the gap between the anvils are coincident to within 0,5 mm (a <0,1 mm).
6.3.8 Axial play in the pendulum bearings shall not exceed 0,25 mm (u c 0.05 mm) measured at the centre-of-rotation under a transverse force of approximately 4% of the effective weight of the pendulum. F5 (see FIgure 4 b)j, applied at the centre of strike.