EN 843-3-2005 pdf download.Advanced technical ceramics – Mechanical properties of monolithic ceramics at room temperature- Part 3: Determination of subcritical crack growth parameters from constant stressing rate flexural strength tests.
Measure the test jag span(s) to the nearest 0,1 mm and, using the travelling microscope or other suitable device (see 5.4.2), check that the relative positions of the rollers are in accordance with the requirements of 5.1. Assemble the lest-jig in the test machine and arrange the environmental control facility as appropnate to the agreed test programme.
Select at least five loading rates coveting at least four orders of magnitude (e.g. 102 N s1, 10’ N s1, 1 N s, 10 N & and 100 N &1), and test at least 10 test pieces at each rate Wi the following manner.
NOTE 1 If the available test machine does not offer preselected constant loading rates (load control). employ cross-head displacement rate control and select five displacement rates covering four orders of magnitude in rate (see 5,3. Note 2).
Insert each test piece m turn in the test jig and carefully align it in accordance with the practice given in EN 843-1. If the tests are being conducted in a controlled environment, unless otherwise agreed allow at least 2 h equilibration of the test-piece In the environment before stressing.
NOTE 2 For chemically corrosive environments it may be desirable closely to define the equilibration period by agreement
If the tests are to be performed in a humid atmosphere, record the relative hianidity. The relative humidity shall not change by more than 10 % during the course of the test series.
Record the ambient temperature. The temperature may be between 15 C and 30 C, and shall not vary by more than 3 K during the test series.
Choose a range for recording the force applied by the testing machine (when necessary) such that the expected mean fracture force is near the centre of the range.
Apply the test force at the chosen rate and record the forceidisplacement relationship and the peak force at fracture Retrieve and identity the broken fragments of test piece for later examination. Clean the test jig of debris, reposition In the test machine and repeat the test on a fresh test piece.
NOTE 3 Subject to agreement between parties It Is possible to shorten the period requwed for testing at slow loading rates by using a faster rate br the initial period 0f loading Caution should be exercised in doing this when testing materials with medium to low values of n or with a wide scatter of strength. For example, the results of tests at higher rates may be used to ind.cate by extrapolation the expected fracture stresses at slower rates, and then the slower tests may commence with fast loading to a maximum stress of approximately half the expected fracture stress. If sucti a procedure is employed it should be tuUy documented In the report.
It the test-pieces are In the as-fired condition (category I), re-measure the width and thickness of the test- piece at the fracture position, and use these data for the calculation of fracture strength.
8 CalculatIon
Calculate the noninal strength of each test-piece from the following equations:
differences in vakies of n and B0 between matenals are not significant because of the propagation of uncertainties in the analysis of this method (see below). This test method is considered appropriate for values of n less than 80.
When using the flexural strength test procedure according to EN 843-1. the error of any mdMdual strength test result small compared with the statistical spread of strengths at any one loading rate. The principal uncertainty In the present results therefore originates from the statistical variation of the strength at each rate. The coefficient of variation of the results Is typicallyt 10 %; for 10 test-pieces at each rate, the standard error of the mean is then approximately ± (standard deviation’n ± 3 %, and the 95 % standard error confidence band Is typically 6 % either side of the mean strength level. This uncertainty is propagated through the least squares line-fitting routine apIed to all data and the different stressing rates, and assuming that a true linear relationship exists, can result in typically ±20 % in the value of n fitted over four orders of magnitude of stressing rate Similar large errors can occur in the value of 8.
This level of uncertainty may appear high, but nevertheless, estimation of n is valuable in determining the relative susceptibility of different materials to different environments, especially for materials selection purposes. Small differences in values of n between materials within those typical uncertainty bands are therefore not significant.
NOTE This document has been drafted taking into account the results of demonstrations in the open literature and two round rotsn exeroses, The results of the round rotirns may be found summarised in (4J and (51.
10 Test report
The test report shall be In accordance with EN ISO/IEC 17025 and shall contain the following Information:
a) name of the testing establishment,
b) date of the test, a unique identification of the report and of each page, the name and address of the customer, and the signatory of the report;
C) reference to this method, I.e. determined in accordance with EN 843-3, and whether the test was in three or four point flexure:
d) description of the test apparatus employed, including jig design, construction mateflals, environmental facility and testing machine;
e) details of the test material type, manufacturing code, batch number, etc.;
f) surface finish category appropriate to the preparation method, i.e. I, H. 111.1, or 111.2;
g) exact method of test piece preparation, including details of the grinding machine, the grinding and finishing operations, grit sizes, directions of grinding and depths or cut, method of chamfering, and any subsequent thermal treatment;EN 843-3-2005 pdf download.