1、raising standards worldwideNO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAWBSI Standards PublicationBS EN 843-8:2010Advanced technical ceramics Mechanical properties ofmonolithic ceramics at roomtemperaturePart 8: Guidelines for conducting prooftestsBS EN 843-8:2010 BRITISH STA
2、NDARDNational forewordThis British Standard is the UK implementation of EN 843-8:2010.The UK participation in its preparation was entrusted to TechnicalCommittee RPI/13, Advanced technical ceramics.A list of organizations represented on this committee can beobtained on request to its secretary.This
3、publication does not purport to include all the necessaryprovisions of a contract. Users are responsible for its correctapplication. BSI 2010ISBN 978 0 580 68822 5ICS 81.060.30Compliance with a British Standard cannot confer immunity fromlegal obligations.This British Standard was published under th
4、e authority of theStandards Policy and Strategy Committee on 31 July 2010Amendments issued since publicationDate Text affectedBS EN 843-8:2010EUROPEAN STANDARD NORME EUROPENNE EUROPISCHE NORM EN 843-8 June 2010 ICS 81.060.30 English Version Advanced technical ceramics - Mechanical properties of mono
5、lithic ceramics at room temperature - Part 8: Guidelines for conducting proof tests Cramiques techniques avances - Proprits mcaniques des cramiques monolithiques temprature ambiante - Partie 8: Lignes directrices de conduite dpreuves Hochleistungskeramik - Mechanische Eigenschaften monolithischer Ke
6、ramik bei Raumtemperatur - Teil 8: Leitlinien zur Durchfhrung von berlast-Prfungen This European Standard was approved by CEN on 13 May 2010. CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a nat
7、ional standard without any alteration. Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN Management Centre or to any CEN member. This European Standard exists in three official versions (English, French, German). A version in
8、 any other language made by translation under the responsibility of a CEN member into its own language and notified to the CEN Management Centre has the same status as the official versions. CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic,
9、 Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom. EUROPEAN COMMITTEE FOR STANDARDIZATION COMIT EUROPEN DE NORM
10、ALISATION EUROPISCHES KOMITEE FR NORMUNG Management Centre: Avenue Marnix 17, B-1000 Brussels 2010 CEN All rights of exploitation in any form and by any means reserved worldwide for CEN national Members. Ref. No. EN 843-8:2010: EBS EN 843-8:2010EN 843-8:2010 (E) 2 Contents Page Foreword 31 Scope 42
11、Normative references 43 Terms and definitions .44 Principle 55 Main considerations 56 Design of proof-test equipment .67 Test operation 78 Report .7Annex A (informative) Basis of proof-testing .9A.1 Short-term strength .9A.2 Long-term effects.9A.3 Defining the need to proof-test . 10Bibliography . 1
12、1BS EN 843-8:2010EN 843-8:2010 (E) 3 Foreword This document (EN 843-8:2010) has been prepared by Technical Committee CEN/TC 184 “Advanced technical ceramics”, the secretariat of which is held by BSI. This European Standard shall be given the status of a national standard, either by publication of an
13、 identical text or by endorsement, at the latest by December 2010, and conflicting national standards shall be withdrawn at the latest by December 2010. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. CEN and/or CENELEC shall not
14、be held responsible for identifying any or all such patent rights. EN 843, Advanced technical ceramics Mechanical properties of monolithic ceramics at room temperature, consists of the following nine parts: Part 1: Determination of flexural strength Part 2: Determination of Youngs modulus, shear mod
15、ulus and Poissons ratio Part 3: Determination of subcritical crack growth parameters from constant stressing rate flexural strength tests Part 4: Vickers, Knoop and Rockwell superficial hardness Part 5: Statistical analysis Part 6: Guidance for fractographic investigation Part 7: C-ring tests Part 8
16、: Guidelines for conducting proof tests FprCEN/TS 843-9, Advanced technical ceramics Mechanical properties of monolithic ceramics at room temperature Part 9: Method of test for edge-chip resistance According to the CEN/CENELEC Internal Regulations, the national standards organizations of the followi
17、ng countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovaki
18、a, Slovenia, Spain, Sweden, Switzerland and the United Kingdom. BS EN 843-8:2010EN 843-8:2010 (E) 4 1 Scope This European Standard describes requirements and methods for proof testing of advanced technical ceramic components. It provides general guidance concerning the design of the test and the met
19、hodology for the selection of loading conditions. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including a
20、ny amendments) applies. EN 843-3, 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 EN 843-5, Advanced technical ceramics Mechanical properties
21、 of monolithic ceramics at room temperature Part 5: Statistical analysis CEN/TS 14425-1, Advanced technical ceramics Test methods for determination of fracture toughness of monolithic ceramics Part 1:Guide to test method selection EN ISO/IEC 17025, General requirements for the competence of testing
22、and calibration laboratories (ISO/IEC 17025:2005) 3 Terms and definitions For the purposes of this document, the following terms and definitions apply. 3.1 delayed failure fracture of an item after an extended period under stress 3.2 item under test component to be subjected to the proof test 3.3 pr
23、oof test short-term test designed to investigate the mechanical or thermo-mechanical potential of a component, removing by fracture those components which do not meet specified levels 3.4 proof-test ratio ratio of the stress to be applied in a short-term proof test to the expected long-term service
24、stress within an item under test NOTE “Item under test“, see 3.2. 3.5 sub-critical crack growth extension of existing cracks or flaws under a stress which does not produce instant failure BS EN 843-8:2010EN 843-8:2010 (E) 5 4 Principle Since advanced technical ceramic components can contain microstr
25、uctural inhomogeneities and mechanical damage which are difficult to detect by non-destructive observations (dye tests, ultrasonics, etc.), an individual component can have insufficient strength to perform adequately in a particular application. The objective of mechanical or thermo-mechanical proof
26、 testing is to determine whether an individual item has adequate mechanical properties before being placed into service. The principle is to apply a short-term stressing operation to the item under test, the level of stress in which exceeds the expected service conditions. Items which fail in this t
27、est, are removed from the population, providing a guarantee of a minimum life in the survivors. The stressing can be directly mechanical, or as a result of thermal stress, such as in a thermal shock test. This guarantee is valid only for the conditions and state of the test piece item under test dir
28、ectly after the proof test. Any change in the material, the geometry or structure of the item after the proof test (e.g. mechanical, thermal, oxidative, corrosive, wear or other damage) can change the strength and can shorten the minimum life of the item. 5 Main considerations The short-term fractur
29、e stress of an advanced technical ceramic component is determined by the most highly stressed microstructural inhomogeneity or discontinuity, and is therefore determined by the method of manufacture and surface finishing. In general, it is not possible to predict with any certainty the forces that c
30、an be applied to a component without risking failure. For some applications where premature failure carries with it considerable costs, it can be beneficial to take steps to minimise the risks by removing from the population of items those individuals which are most at risk from failure. Additionall
31、y, many types of advanced technical ceramic suffer from the slow growth of small cracks under maintained stress, with a consequent loss of the remaining strength. This thermally activated process may be accelerated by the presence of water, or by a corroding environment, which can react with the cry
32、stalline or amorphous bonding at the tip of crack. Thus if a component is held under stress for a prolonged period, it can weaken with time and lead to delayed failure. The tendency of a material to behave in this way can be detected, for example, by undertaking strength tests at different stressing
33、 rates (see EN 843-3) or by statically stressing the material until failure occurs. Generally, the effect is most marked in silicate glasses, and in glass-phase containing oxide ceramic materials. It is less marked in purely crystalline oxide ceramics, and least marked in non-oxide ceramics. The pri
34、nciple of the proof-test (see Annex A) is to stress the item to such a level as will probe the item to determine the presence of features that would result in low strength. The stress distribution should ideally match that seen in the application of the item, and should be applied smoothly and quick
35、ly, and then removed in a similar manner such that the strength of the surviving items is not reduced by non-catastrophic crack growth. There are several philosophies that can be adopted: a) Select a stress level which pragmatically removes a certain fraction of the population, by a few percent, pro
36、viding a guaranteed minimum strength for the remainder. b) Select a stress level which is a factor of typically two or three times the expected stress level in service, providing a greater assurance that it will survive in service. c) Numerically determine the over-stress level factor from the fract
37、ure mechanical behaviour of the material, specifically the critical stress intensity factor (see CEN/TS 14425-1) and the sub-critical crack growth characteristics (see EN 843-3), combined with Weibull parameters (see EN 843-5) to provide stress-volume or stress-area predictions of the risk of failur
38、e. This method, while scientifically rigorous, is time-consuming and effective only if the fracture mechanical data that can be acquired are applicable to the item in every respect. NOTE Components may be produced and finished in ways which are not equivalent to the conditions employed for manufactu
39、ring, and testing test pieces of closely defined geometry, and thus may vary in density, microstructural homogeneity, surface finishing and residual stress levels. Predictions may be poor unless the equivalence is good. BS EN 843-8:2010EN 843-8:2010 (E) 6 Of these three philosophies, a) and b) are p
40、ragmatic and can be set by simple judgement. They are typically used to ensure that each item, as supplied, has adequate strength at the point of delivery, but the procedures take no account of the potential of the material to age in service and to fail as a consequence of progressive loss of remain
41、ing strength with time. The third philosophy, c), additionally takes the slow loss of strength into account, and has been used successfully on safety-critical components under long-term stress. The effectiveness of a proposed proof-testing method can be determined by evaluating the short-term streng
42、th distribution of proof-tested items compared with the strength distribution before proof testing. In the prior proof-tested batch, there should be an absence of items failing at less than the set proof-test level. The continued presence of items failing at less than the proof-test level is an indi
43、cation that there is some weakening of items during the proof-test, which either has to be taken into account in selecting the proof-test loading level, or the proof-test schedule itself has to be examined to reduce or eliminate the effect. Overload proof-testing will not be successful in guaranteei
44、ng a component in service in the following circumstances: where the item becomes damaged in service, particularly where such damage is in regions of high stress; where the stresses in service are poorly defined or undefined, such as shock loading, or localised hard contact; where temperature changes
45、 are significant; where the item has features that would suffer unduly in overload proof-testing, such as sharp edges, joints to other materials or surface coatings, or marking of items by the testing system; where the stress distribution under the service conditions cannot be conveniently modelled
46、in a proof-testing situation; where proof-testing cannot be performed quickly and smoothly, particularly the unloading part of the cycle; where it may not be possible adequately to design an overload thermo-mechanical proof-test because of temperature limitations, oxidation, or unknown or undefinabl
47、e heat transfer conditions. The principal considerations are therefore the design of the system for undertaking the proof-test, and ensuring that it adequately matches the service stress condition during item testing. 6 Design of proof-test equipment The principal factors in the appropriate design o
48、f proof-testing equipment are: clear understanding of service conditions to be experienced by the item under test, and the lifetime to be expected; definition of the stress distribution to be achieved in the item during testing; definition of and agreement concerning the overload factor to be employ
49、ed; evaluation of methods of achieving the stress distribution in a non-destructive manner; design of a proof-testing system which provides the appropriate stress distribution without otherwise marking or damaging the items under test. Ideally, the proof-testing system should incorporate the following features: BS EN 843-8:2010EN 843-8:2010 (E) 7 easy insertion and removal of the item to be tested; contacts between the item under test and metallic parts
