1、 SAE/USCAR-7 Revision 1 Deembrittlement Verification TestJuly 2012ISBN: 978-0-7680- - 7883 1_The research data, analysis, conclusion, opinions and other contents of this document are solely the product of the authors. Neither the SAE International (SAE) nor the United States Council for Automotive R
2、esearch (USCAR) certifies the compliance of any products with the requirements of nor makes any representations as to the accuracy of the contents of this document nor to its applicability for purpose. It is the sole responsibility of the user of this document to determine whether or not it is appli
3、cable for their purposes.Copyright 2012 USCAR Printed in U.S.A. All rights reserved. QUESTIONS REGARDING THIS DOCUMENT: (248) 273-2470 FAX (248) 273-2494 TO PLACE A DOCUMENT ORDER: (724) 776-4970 FAX (724) 776-0790 SAE/USCAR-7 REVISION 1 Issued 1998-12 Reaffirmed 2012-07 DEEMBRITTLEMENT VERIFICATION
4、 TEST 1. SCOPE: This standard outlines test methods and practices which can detect embrittlement of steel parts. It is a process control or referee verification test. The risk of embrittlement of steel is minimized by using best practices in the finishing/coating process. One such practice is descri
5、bed in SAE/USCAR-5, Avoidance of Hydrogen Embrittlement of Steel. 2. REFERENCES: 2.1 SAE Publications: Available from SAE, 400 Commonwealth Drive, Warrendale, PA 15096-0001. SAE/USCAR-5, Avoidance of Hydrogen Embrittlement of Steel 3. DEEMBRITTLEMENT TEST A torque/tension test is used for threaded p
6、arts and a tensile test is used for non-threaded parts. The test consists of three steps: 1) Determine the ultimate torque or tensile stress to failure for threaded and non-threaded parts respectively; 2) Load the parts to some percentage of the ultimate torque or tensile stress; 3) Maintain the tor
7、que or tensile stress for some determined length of time. Whenever possible, the test fixture should simulate the intended application. Section 3.5 discusses alternatives to test fixtures. SAE/USCAR-7 REVISION 1 Reaffirmed 2012-07 DEEMBRITTLEMENT VERIFICATION TEST - 2 - 3.1 Test Load Determination 3
8、.1.1 Threaded Parts a. Randomly select a minimum of 5 parts from the lot being evaluated to establish the test torque for the stress test. Note that the five part sample is only to establish the test torque used for the deembrittlement tests. The deembrittlement test sample size is discussed in sect
9、ion 3.2. b. Apply torque to the test part, or the mating part of the text fixture until ultimate failure of the test part occurs. Some ideas of fixturing methods are discussed in Section 3.5. Hand or power tool tightening is acceptable, however, the selected tightening method must also be used in pe
10、rforming the deembrittlement test (section 3.3). Record the maximum torque for each of the five fasteners. The average maximum torque for all five test parts is the ultimate failure torque which completes step 1 referred to in section 3. c. The test torque to be used in step 2, referred to in sectio
11、n 3., is 80% of the ultimate failure torque. This test torque value does not necessarily correspond to the actual application installation torque for the part. 3.1.2 Non-Threaded Parts a. Randomly select a minimum of 5 parts from the lot being evaluated. (Note that the five part sample is only to es
12、tablish the test load used for deembrittlement tests.) The deembrittlement test sample size is discussed in section 3.2. b. Determine an acceptable tensile test method for the geometry and configuration of the part. The test fixture and test procedure must be agreed upon by the supplier and the purc
13、haser. Some ideas on fixturing methods are discussed in section 3.5. Apply a tensile load to the part until failure of the test part occurs. Record the maximum tensile load for each of the five parts. The average maximum load for all five test parts is the ultimate load which completes step 1. The f
14、ixture and test method used for step 1 must be duplicated for steps 2 and 3. Steps 1, 2, and 3 are described in section 3. c. The tensile load used in step 2, referred to in section 3., is to be some percentage of the ultimate load. Typical test loads are between 70 to 80 percent of the ultimate loa
15、d. The supplier must determine a test load sufficient to detect embrittlement susceptibility. At a minimum, the test load should exceed the tensile load applied during assembly of the part into its actual application. SAE/USCAR-7 REVISION 1 Reaffirmed 2012-07 DEEMBRITTLEMENT VERIFICATION TEST - 3 -
16、3.2 Sample Size Determination A lot for the purpose of the deembrittlement test is defined as follows. For a batch oven, a lot is a load of baked parts with the same part number. For a continuous baking furnace, a lot (for a particular part number) is to be defined by the supplier as is agreeable wi
17、th their process; keeping in mind that if a failure should occur during the subsequent deembrittlement test, the lot shall be scrapped. The lot shall be defined such that all processing traceability is maintained for each part number/lot identification. The number of parts to be subjected to the dee
18、mbrittlement test must be determined by agreement between the supplier and purchaser. The control plan will specify the test sample size. 3.3 Performing Deembrittlement Test 3.3.1 The total number of parts determined in section 3.2 are to subjected to the deembrittlement test. 3.3.2 These parts are
19、to be loaded using the same fixture, the same loading methods and the same test load determined in paragraph 3.1.1 for threaded parts or paragraph 3.1.2 for non-threaded parts. Parts which fail while attempting to be assembled to the test load (torque) should be discarded and cannot be counted as pa
20、rt of the test lot. 3.3.3 These parts are to be held at load in the fixture as described below. a. For threaded parts: Reapply test torque after the parts have been held for 24 hours. If any failures occur at this 24 hour check, the test is to be terminated and the entire lot shall be rejected as de
21、scribed in paragraph 3.4. If no failures occur, continue to hold the parts at load for an additional minimum of 24 hours, reapply test torque then remove from the fixture and examine per paragraph 3.4. b. For non-threaded parts: Hold the parts at load in the fixture for a minimum period of 48 hours.
22、 Remove from the fixture and examine per paragraph 3.4. 3.4 Pass/Fail Determination Visually inspect the parts which have undergone the 48 hour test. The parts should be free of cracks or multi-piece fractures. If cracking or fracturing has occurred on one or more of the samples, the entire lot shal
23、l be rejected and scrapped (no rework of these parts is allowed). If none of the sample parts have cracked or fractured, the process is considered to be in control for that lot and therefore can be shipped. 3.5 Fixturing Methods The following suggestions are provided to assist in establishing the te
24、st load and method of test to induce high tensile stress for performing the deembrittlement test. SAE/USCAR-7 REVISION Reaffirmed 2012-07 DEEMBRITTLEMENT VERIFICATION TEST - 4 - 3.5.1 Screws may be seated against a 4 degree wedge to represent a worst case assembly condition. 3.5.2 A flat washer may
25、be inserted between the screw and the wedge test plate to eliminate the effects of torque robbing serrations, rings, etc. which may prevent torquing the fastener to failure due to socket cam off or recess bit cam out. (Note that the washer I.D. should not be larger that 0.04 in (1.0 mm) over the maj
26、or diameter of the screw.) The O.D. of the washer should be equal to or greater than the maximum flange diameter of the screw being tested. 3.5.3 Large diameter threaded fasteners may be lubricated to reduce the torque required to fail the fastener and establish the test torque. If lube is used, the
27、 same lube must be used and applied for the entire test. 3.5.4 Screws with internal drives which cannot be torqued to failure due to bit cam out or failure, may be tested to a torque equal to 80% of the average torque achieved at cam out or bit failure. This will be considered the failure torque for
28、 the deembrittlement test for this fastener. 3.5.5 Tapping screws may be tested using pre-threaded holes in test plates to achieve screw failures instead of thread strippage. 3.5.6 Screws may be tested by applying torque to head of the screw or to a nut if a nut is used as part of the test set up. 3
29、.5.7 Flat and coned washers, pre-assembled or loose, can be tested on a fixture having an oversize clearance hole so that the washer inverts and therefore induces high tensile stress to the convex surface. Washers are to be loaded over a hole diameter equal to 80% of the minimum outside diameter of
30、the washer. The loading device or bolt hex size being used to load the washer should not be greater than 1.5 times the inside diameter of the washer. Five washers must be loaded to the yield strength of the material. Eighty (80%) percent of this average load is the test load for the deembrittlement test. 4. KEYWORDS: Fastener, Hydrogen, Delayed Failure PREPARED BY THE USCAR FASTENER TECHNICAL COMMITTEE 1
