ENGINEERING STANDARDS Test Method Materials GMN3922 Specifying Conditions for Compressive Stress Relaxation Testing of Rubber and TPE (90 A) ? Copyright 2005 General Motors Corporation All Rights Reserved August 2005 Originating Department: North American Engineering Standards Page 1 of 7 1 Scope This document describes test procedures and conditions for determining the loss in counter- force of a standard specimen shape com- pressed at a constant deformation in specified media, under conditions of time and tempera- ture. It is designed for testing of (a) specimens of vulcanized rubber, and thermoplastic elas- tomers with instantaneous Shore A hardness from 45 to 90 (ASTM D2240), cut from standard sheets (ASTM D3182) and (b) finished produc- tion articles of same hardness range (e.g. molded profile o-ring) per ASTM D3183. Note: Nothing in this procedure supersedes ap- plicable laws and regulations unless a specific exemption has been obtained. Note: In the event a conflict between the English and domestic language, the English language shall take precedence. 1.1 Purpose. 1.1.1 This document is a supplement to ASTM D6147 and ISO 3384 procedures for compres- sive stress relaxation (CSR) testing. 1.1.2 Supplements. Supplemental features in- clude; a. Mandatory classification of test conditions and requirements using a “line call-out” des- ignation. See 7.2, 7.3. b. Authorized Fixtures. See item 3.2. c. For referee purposes, a designated system with data acquisition to provide continuous counter-force measurement for the speci- fied test duration. See item 3.2.3. 1.2 Foreword. This document uses two meth- ods to measure counterforce; discontinuous (manual) or continuous (using force washers, etc.) at the specified media and test tempera- ture. They differ significantly from Method A and B of ASTM D6147 and ISO 3384. Both GM methods load and start at the same tempera- ture, but the end temperature measurements differ. 1.2.1 Method A (Manual – m or Continuous – c at 23 °C). The test specimen compression and the initial measurement of the counterforce take place at 23 ± 2°C; the test specimen is then stored in a chamber controlled at the test tem- perature, but it is removed from the chamber (or lowered to temperature) for each of the subse- quent force measurements, which are made at 23 ± 2°C. This is the only method for manual measurement of counterforce subjected to iso- thermal or cyclic temperatures. It is the most common method used for generating CSR data. 1.2.2 Method B (Continuous at Temperature). The test specimen compression and the initial measurement of the counterforce take place at 23 ± 2°C; the test specimen is then stored in a chamber controlled to the test temperature or cycle. Measurements are made on a continuous basis at the designated temperatures. When designating this method, you are requiring con- tinuous measurement equipment. Make sure your source has access to this equipment. 1.3 Applicability. 1.3.1 When specifying retained force for your compound, consider its minimum contribution in relation to design, construction, and assembly. These contributions are not always equal. 1.3.2 Under constant load (strain), rubber forms new crosslinks resulting in permanent physical deformation (change in shape). The intensity (stress) of the internal forces at constant defor- mation decreases over time and temperature. Stress relaxation is that measure of loss in force (stress) or the amount retained as a percent of the initial stress. This information is of practical value for studying materials for gaskets, hose clamped or with end fittings and other com- pressed applications. 1.4 Definitions. Compressive Stress, n – the time-dependent force necessary to maintain a constant com- pressive strain, divided by the original cross- sectional area over which the force is applied. Force Decay, n – the decrease in stress which has occurred after a specified time-interval, dur- Copyright General Motors North America Provided by IHS under license with GM Licensee=IHS Employees/1111111001, User=Japan, IHS Not for Resale, 06/24/2008 00:28:39 MDTNo reproduction or networking permitted without license from IHS --```,`,``,,`,,`,,``,``````,,-`-`,,`,,`,`,,`--- GMN3922 GM ENGINEERING STANDARDS ? Copyright 2005 General Motors Corporation All Rights Reserved Page 2 of 7 August 2005 ing application of a constant deformation, ex- pressed as a percentage of the stress at the commencement of that time-interval. (Stress relaxation is a synonym). Thermoplastic Elastomer, n – See ASTM D883 definition. 2 References Note: Only the latest approved standards are applicable unless otherwise specified. 2.1 External Standards/Specifications. ASTM D395 IEC 811 ASTM D471 IEEE/ASTM SI 10-97 ASTM D572 ISO 188 ASTM D883 ISO 1629 ASTM D892 ISO 3384 ASTM D1418 ISO 6056 ASTM D2240 ISO 17025 ASTM D3182 QS 9000 ASTM D3183 SAE AS568 ASTM D4678 SAE J2232 ASTM D5423 SAE J2236 ASTM D6147 2.2 GM Standards/Specifications. GM4653M GM6417M GM4718M GM6418M GM6137M GM9505P 3 Test Equipment 3.1 Facilities. A suitable area or room for con- ducting testing with a stable and known envi- ronment. See 4.2.1. 3.2 Equipment. Use only the 3M/Dyneon LLC fixture for discontinuous testing in any media. This fixture meets ISO 3384 and ASTM D6147 requirements. For the 13 mm disk (Do) the stan- dard jig includes base, cap and cap screws. Centering cup, wedges (3), shims, and indentor pin are extra. A fixture to accommodate the SAE AS568-214 o-ring includes base, cap and cap screws. Larger centering cup, wedges (3), shims, and indentor pin are extra. Note: Fixture available from Classic Manufactur- ing Inc. 2980 Granada Lane North, Oakdale, MN 55128. Phone 651 770-1212. 3.2.1 See ASTM D6147 or ISO 3384 apparatus section. Each fixture must have a means to cen- ter the D0 specimen before, during, and after loading is complete. Figure 1: CSR Fixture Components Figure 2: CSR Centering Elements 3.2.2 For referee purposes use the EB02 Re- laxation Tester available from Elastocon AB, G?teborgsv?gen 99, SE-504 60 BOR?S, Swe- den. E mail: www.elastocon.se. Relaxation test- ers are used in combination with cell oven EB 01 or EB 07 when testing at temperature. Run two test specimens when using this tester. 3.2.3 The 3M/Dyneon LLC and Elastocon test fixtures accept button and o-ring test specimens. 3.2.4 Ovens. Precise cabinet temperature con- trol obtained through air exchange and circula- tion uniformity (in time and space) is critical to measurement repeatability and reproducibility at isothermal temperatures. Small units capable of obtaining ± 1.0°C around a set temperature are best suited for CSR measurement. Select ovens with air exchange rates of 3 to 20 changes/h meeting ISO 188 and IEC 811 or ASTM D5423 type I requirements. Indentor Pin Clamping Bolts Clamping Plate CSR Base Shims Test Specimen Centering Cup Centering Wedges Copyright General Motors North America Provided by IHS under license with GM Licensee=IHS Employees/1111111001, User=Japan, IHS Not for Resale, 06/24/2008 00:28:39 MDTNo reproduction or networking permitted without license from IHS --```,`,``,,`,,`,,``,``````,,-`-`,,`,,`,`,,`--- GM ENGINEERING STANDARDS GMN3922 ? Copyright 2005 General Motors Corporation All Rights Reserved August 2005 Page 3 of 7 3.2.5 Pressure Vessel. Use device described in ASTM D572 for coolant testing. See 4.1.4.4 and Figure 3. Note: Available from Parr Instrument Company, 211 Fifty Third Street, Moline, Illinois 61265- 9984. Phone: 1-800-872-7720/(309) 762-7716 FAX (309) 762-9453. Email:
[email protected] 3.2.5.1 Basket for Test Jigs (optional and info). In a suitable sized Parr Pressure Vessel, the two liter basket holds eighteen jigs. Figure 3: Pressure Vessel and Basket 3.3 Test Vehicle/Test Piece. 3.3.1 Follow the test specimen section of ASTM D6147, including the remaining items in this sec- tion. Use 3 specimens per test (see 3.2.3 refe- ree device). Specimen dimensions are given in Table 7. 3.3.2 Mold D0 specimens to the dimensions in Table 7. Make four thickness measurements approximately 90 degrees apart. Discard the specimen if any one of the four measurements vary more than 0.02 mm. Measure using a met- ric dial gauge in a central area to avoid edge effects. 3.3.3 Do not use metal spacers to maintain a set sample compression, use the average of the four specimen thickness readings to calculate each spacer height. For specimens requiring 25% compression, multiply the average speci- men height in mm by 0.75 to determine the spacer height. 3.3.4 The D0 specimen shape factor (Table 7) is 0.50 to provide consistent results. Sample type (shape factor) will affect test results. Com- pare data only from the D0 specimen size and shape tested in identical fixtures (see 3.2). 3.3.5 Lubricate test specimen before compres- sion. Use a silicone fluid. Note: Dow Corning Corp. 200 silicone fluid meets the requirements. 3.3.6 Ring profile Specimens (see Table 7) – For O-Ring Specs Only. A test fixture base can be modified to accommodate production part profiles provided it allows the required compres- sion level and doesn’t affect test results. Indicate any modification in test reporting section. 3.3.7 O-Ring Specimens (see Table 7) – For O- Ring Specs Only. If production-size rings are too small or large to fit the fixture, use the appropri- ate SAE AS 568 size o-ring. 3.3.7.1 Use 15% compression for o-ring speci- mens. 3.4 Test Time. 3.4.1 Calendar Time. The typical duration is 42 days. 3.4.2 Test Hours. The duration of the test shall be mutually agreed upon by the customer and the supplier. The line call-out (item 7.2) identifies the test time and duration using Table 3. Se- quence 2 has been found suitable for many elastomers. The test period begins after the ini- tial compression. In method A, the 2 h required after each time-interval, to attain standard labo- ratory temperature, shall be included in the dura- tion of test. 3.4.3 Coordination Hours. Approximately 2 days to prepare test specimens and fixtures. 3.5 Test Required Information. 3.5.1 To simplify test requirements for specification purposes, use the following tables to identify the compound type, test method, test temperature, test media. 3.5.2 Compound. The compound shall be of the type specified by the initial letters of the line call- out, as shown in Table 1. Use ASTM D1418 or ISO 1629 to expand table with appropriate symbols. Thermoplastic elastomers use TPE as the identifier. Copyright General Motors North America Provided by IHS under license with GM Licensee=IHS Employees/1111111001, User=Japan, IHS Not for Resale, 06/24/2008 00:28:39 MDTNo reproduction or networking permitted without license from IHS --```,`,``,,`,,`,,``,``````,,-`-`,,`,,`,`,,`--- GMN3922 GM ENGINEERING STANDARDS ? Copyright 2005 General Motors Corporation All Rights Reserved Page 4 of 7 August 2005 Table 1: Compound Type (ASTM D1418, SAE J2332) Compound Symbol Compound Description Note 1 ACM Polyacrylate AEM Ethylene/Acrylic BR Butadiene rubber CO Epichlorohydrin (homopolymer) CM Chlorinated polyethylene CSM Chloro-sulfonyl-polyethylene EPDM Ethylene Propylene Diene Ter- polymer ECO Epichlorohydrin copolymer FEPM Tetrafluoroethylene-propylene FKM Fluoroelastomer FVMQ Fluorosilicone HNBR Hydrogenated nitrile NBR Acrylonitrile butadiene rbr. NPVC Nitrile + PVC VMQ Silicone TPE Thermoplastic Elastomer Note 1: See SAE J2332 for trademark names for these ge- neric materials. 3.5.3 Test Method. The method shall be of the type specified by the initial letters of the line callout, as shown in Table 2. Table 2: Test Method Method Symbol Description (See 1.2.1 – 1.2.2) AM Specimen compressed and meas- ured at 23°C temperature manually. AC Specimen compressed and meas- ured at 23°C temperature with force washer. BC Specimen compressed and meas- ured initially at 23°C with a force washer. Further measurements taken at designated temperatures and times. 3.5.4 Test Time. The measurement sequence and total duration test time shall be specified by the number of the line call-out, as shown in Ta- ble 3. Readings 30 minutes after initial compres- sion are implied in each sequence. 3.5.5 Air Test Temperature for Compound Under Test. The air only measurements are conducted at the maximum temperature indi- cated for the materials shown in Table 4. Unless otherwise specified, selection of the compound dictates the corresponding test temperature (de- fault). The upper temperature limits are based on SAE J2236 requirements and apply only to methods A and B. The table compound tem- peratures are not completely representative of some compound upper limits. Fixture and force washer measurement reproducibility and durabil- ity influenced the selection. Table 3: Test Measurement Time & Duration Sequence Number Description 1 Measurement at 24, 72, 168, 336 and 504 h. 2 Measurement at 24, 72, 168, 504, 840 and 1008 h. 3 Measurement at 24, 168, 504, 1008, 1512 and 2016 h. 4 Measurement during GMW3155TP cycle. Due to the length of the test, the re- quester and tester must agree on measured intervals. 5 As specified to end of test (EOT). Table 4: Air Test Temperature Compound Sym- bol Max. Test Temperature °C ACM 150 AEM 150 BR 100 CO 125 CM 125 CSM 125 EPDM 150 ECO 125 FEPM 150 FKM 150 FVMQ 150 NBR 125 HNBR 150 NPVC 100 VMQ 150 TPE 125 ZA value as specified in °C 3.5.6 Test Temperature for Fluid Under Test. Unless otherwise specified, measurements are conducted at the recommended temperature indicated for the fluids shown in Table 5. The Copyright General Motors North America Provided by IHS under license with GM Licensee=IHS Employees/1111111001, User=Japan, IHS Not for Resale, 06/24/2008 00:28:39 MDTNo reproduction or networking permitted without license from IHS --```,`,``,,`,,`,,``,``````,,-`-`,,`,,`,`,,`--- GM ENGINEERING STANDARDS GMN3922 ? Copyright 2005 General Motors Corporation All Rights Reserved August 2005 Page 5 of 7 selected temperature limits are based on health and safety considerations with an interest in maintaining test consistency. Fixture and force washer measurement reproducibility and dura- bility also influenced the selection. Caution: Federal, state, local or company re- strictions and regulations must be observed and followed. These temperatures are only recom- mended guidelines. It is the responsibility of the tester to follow item 6 statement. 3.5.6.1 Test Fluid Replacement. Table 5 also lists the replacement frequency in hours for test fluids at maximum temperatures. It is not our intent to match customer oil change frequency behavior or use this test to measure oil life ex- pectancy. Table 5: Recommended Fluid Test Tempera- tures & Replacement Media Symbol Max. Test Tem- perature °C Change in h 9 150 Unlimited B 125 every 168 EC 125 every 168 O1 150 1008 O2 150 504 S1 150 504 T1-2 150 1008 ZF As specified. 1008 3.5.7 Test Media. The media shall be of the type specified by the initial letter(s) or number(s) of the line call-out, as shown
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