1、_SAE Technical Standards Board Rules provide that: “This report is published by SAE to advance the state of technical and engineering sciences. The use of this report is entirely voluntary, and its applicability and suitability for any particular use, including any patent infringement arising theref
2、rom, is the sole responsibility of the user.” SAE reviews each technical report at least every five years at which time it may be reaffirmed, revised, or cancelled. SAE invites your written comments and suggestions. Copyright 2011 SAE International All rights reserved. No part of this publication ma
3、y be reproduced, stored in a retrieval system or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of SAE. TO PLACE A DOCUMENT ORDER: Tel: 877-606-7323 (inside USA and Canada) Tel: +1 724-776-4970 (outside US
4、A) Fax: 724-776-0790 Email: CustomerServicesae.org SAE WEB ADDRESS: http:/www.sae.orgSAE values your input. To provide feedback on this Technical Report, please visit http:/www.sae.org/technical/standards/J2661_201105SURFACEVEHICLERECOMMENDEDPRACTICEJ2661 MAY2011 Issued 2011-05Optical Imaging Evalua
5、tion of Impact Damage Resistance Testing on Exterior Finishes RATIONALEThe ISO method is designed only for exterior coatings material. SAE J2661 is a more comprehensive method that covers not only the exterior coatings materials but also exterior plastics, coatings, paints, plastic sheeting material
6、s and so on. The ISO method is not comprehensive in its description of how the evaluation is performed. The SAE method describes details of performance not covered in the ISO method, base on the input of American automakers and their suppliers. The American automakers perform a slightly different ty
7、pe of stone chipping test (Gravelometer Test) compared to the rest of the world due to the road conditions in the U.S. SAE J2661 is technically equivalent to ISO 21227-2. 1. SCOPE This SAE Recommended Practice covers a procedure for evaluating plastic and multiple-layer coatings exposed to gravelome
8、ter testing (as defined in SAE J400) with an optical imaging and analysis system. The intent of the procedure is to detect, count and characterize instances of damage in the coated surface that fracture the top coat layer or penetrate through multiple layers of the coating system. It may be possible
9、 to extend this methodology of coating damage evaluation to specimens that have undergone test procedures or exposures that produce similar, discrete damage sites in the coating system. If so applied, evaluation results must be interpreted with respect to the limitations and intent implied by the or
10、iginal evaluation procedure and its associated rating system, if applicable. 1.1 Applicability This method may be applied to the evaluation of surface damage on plastic and coated surfaces caused by means other than gravelometer testing; provided that the specimen substrate is not significantly defo
11、rmed to a degree that would prevent all surface damage sites from remaining in a single focal plane capable of being adequately resolved by the image capturing device.1.2 Application This SAE Recommended Practice covers a procedure for evaluating plastic and multiple-layer coatings exposed to gravel
12、ometer testing (as defined in SAE J400) with an optical imaging and analysis system. The intent of the procedure is to detect, count and characterize instances of damage in the coated surface that fracture the top coat layer or penetrate through multiple layers of the coating system. It may be possi
13、ble to extend this methodology of coating damage evaluation to specimens that have undergone test procedures or exposures that produce similar, discrete damage sites in the coating system. If so applied, evaluation results must be interpreted with respect to the limitations and intent implied by the
14、 original evaluation procedure and its associated rating system, if applicable. SAE J2661 Issued MAY2011 Page 2 of 10 2. REFERENCES 2.1 Related Publications The following publications are listed for information purposes only and are not a required part of this SAE Technical Report.2.1.1 SAE Publicat
15、ions Available from SAE International, 400 Commonwealth Drive, Warrendale, PA 15096-0001, Tel: 877-606-7323 (inside USA and Canada) or 724-776-4970 (outside USA), www.sae.org.SAE J400 Test for Chip Resistance of Surface Coatings 2.1.2 ISO Publications Available from American National Standards Insti
16、tute, 25 West 43rd Street, New York, NY 10036-8002, Tel: 212-642-4900, www.ansi.org.ISO 21227-21Paints and varnishes Evaluation of defects on coated surfaces using optical imaging Part 2: Evaluation of multi-impact stone chipping test 3. SUMMARY OF METHOD Tested specimens are digitally captured unde
17、r predetermined (software controlled) Illumination geometries. The images are then processed to highlight the damage sites. Subsequent processing may be applied to separate out the damage sites layer-by-layer on specimens having multi-layer coatings. The damage sites are then automatically measured
18、and analyzed geometrically (by a software program) to derive statistical characteristics. The ratio of the damaged area to the total evaluated area on the sample specimen is measured and recorded as a percentage. If desired and within the capability of the analysis program, other quantitative variab
19、les may be determined. This data is then saved to disk. The procedure above may also be applied to reference specimens, ultimately allowing a rating of the test specimens by comparing their statistical data with those of the numerically ranked reference specimens. The reference samples shall be as s
20、imilar as possible to the samples to be tested, as far as material formulation, structure, finish and contrast of the individual layers (in coating systems) are concerned; therefore they shall be made using real resources and systems subject to strict quality control. During the evaluation procedure
21、, optimal specimen illumination and image processing conditions are established and their software settings shall be savable to disk. This allows them to be recalled, ensuring stable and reproducible evaluation conditions specimen-to-specimen, especially critical if the evaluation procedure is inter
22、rupted or conducted over multiple sessions. 1To be published. SAE J2661 Issued MAY2011 Page 3 of 10 4. EQUIPMENT 4.1 Optical Imaging System 4.1.1 Hardware The hardware shall include an image capturing device, fixed-geometry illumination source or sources, and a means for performing the capture of sp
23、ecimen surface images in the absence of ambient light. Illumination source and imaging control shall be provided by computer software to allow accurate reproducibility of the image capture conditions. 4.1.1.1 Image Capture Device This component shall include a charge coupled device (CCD, or CCD chip
24、) providing an imaging resolution of 10 pixels/mm and the capability to record 8 bit/pixel grayscale (256 shade) images. The viewing lens shall be fixed-focal length type with a fixed aperture to ensure identical image capture magnification and prevent variations in the detection resolution. A vibra
25、tion damping mounting shall be included to ensure optimal image clarity. 4.1.1.2 Illumination Sources Typical geometries shall include provisions for selecting the desired source and the ability to adjust its illumination intensity. Geometries shown to be suitable for this purpose are direct illumin
26、ation (to allow capturing of specular reflection characteristics) and diffuse illumination (to allow capturing of chromatic reflection). Direct illumination is capable of illuminating the specimen surface at a 0 degree incident angle. In plastic specimens, this allows optimal detection of surface ir
27、regularities. In coated specimens it allows detection of specimen topcoat (clearcoat) damage without influence from reflections originating in pigmented sub layers. (Direct illumination reflects from the surface of the clear topcoat layer and provides image information only from that layer.) Diffuse
28、 illumination provides a means for highlighting (optimizing contrast) between pigmented coating layers to facilitate their differentiation in the specimen image damage sites (a capability critical for detecting and analyzing such defects extending through multiple coating layers). For advanced analy
29、sis on a layer-by-layer basis, the application of direct and diffuse illumination sources may be combined to allow comprehensive characterization of specimen surface damage. Since the influence of variable ambient lighting would render the specimen illumination unreliable and irreproducible, the ima
30、ge capture shall be performed in a dark box or similar light-proof enclosure housing the illumination sources and image capture device. 4.1.1.3 Illumination Source Calibration Prior to conducting an evaluation, the spectral characteristics of the illumination sources shall be verified to a traceable
31、 source. An appropriate spectral measuring device shall be mounted to acquire its readings in the same plane and at the same distance from the illumination source(s) as that of the test specimen surface during an image capture procedure. As well, the illumination intensity across the region viewed b
32、y the capture device shall exhibit a verifiable uniformity no greater than 5%. Imaging system manufacturers typically include a methodology for verifying these functional characteristics of the illumination sources. 4.1.1.4 Specimen Indexing Capability If the region of interest (ROI) to be evaluated
33、 on the sample surface exceeds the viewing region of the image capture device, a means shall be provided for reliably indexing (incrementally moving) the specimen so that sequential image captures may be performed; such that the entire ROI is captured in segments (multiple images). This may be achie
34、ved with movable fixturing to which the test specimen is fastened and its positional adjustment within the capture region performed either manually by the operator or automatically via software program control driving servo indexing motors. The fixturing shall be anchored to the system so that its i
35、ncremental movements are precise, consistently repeatable and preventive of image overlap. To accommodate such an indexing device, the image processing software shall include a routine for stitching partial, segmented specimen images into a single image. SAE J2661 Issued MAY2011 Page 4 of 10 4.1.2 S
36、oftware The software program shall provide an operator interface allowing control of the system illumination sources, the image capturing device and the specimen indexing fixture (where applicable). It may also provide features that allow image processing for optimization of specimen image appearanc
37、e and surface defect clarity and contrast. For defect analysis, the software shall provide a means for differentiation and automated detection of the grayscale values exhibited by damage sites in polymer surface images, as well as the various exposed layers within damage sites of a coated-specimen i
38、mage. The software shall also be capable of geometrically defining (measuring) such damage regions with regard to surface area and of automatically counting their instances of occurrences throughout the image. All such setup and analysis settings shall be recordable in a configuration file so that i
39、nterrupted or subsequent evaluations may be performed under the exact same conditions (i.e., under the same illumination, grayscale image processing/enhancement and analysis schemes). 4.1.2.1 Illumination Control For the illumination geometries, controls shall be provided to allow a selection betwee
40、n direct and diffuse sources. Additional controls shall be included to allow precise and repeatable adjustment of the source llumination intensity. 4.1.2.2 Image Capture Device Control A means shall be provided in the software program for remote activation of the capture device to ensure a vibration
41、-free capture.4.1.2.3 Specimen Indexing Control Where applicable, the software shall allow remote control of the motorized indexing fixture for the acquisition of multiple specimen images. If a non-motorized fixture is in use, it is allowable to have the operator adjust its position by hand if the f
42、ixture meets the requirements specified in 4.1.1. 4.1.2.4 Image Processing and Analysis The software shall include an automated function for executing a thresholding procedure on the specimen image. This causes pixels within a selected grayscale range to change to black. The function of this is to s
43、egregate the pixels that represent surface irregularities (damage sites) in plastic surface images from the background (or undamaged region), or the exposed surface of a coating layer within a damage site from the other layers in that site and from the background. These pixel groups may then be geom
44、etrically characterized (damage area quantified and their frequency within the image enumerated), as well as quantified and characterized (where applicable) on a layer-by-layer basis throughout a coating system via a threshold-based particle size analysis. Examples of a captured specimen image (Figu
45、re 1) and damage pixels segregated by thresholding (Figure 2) are shown below. (The images of Figure 2 have been inverted for presentation clarity.) The software shall provide an adjustable algorithm for executing these functions automatically; the user settings for which may be saved to disk in a c
46、onfiguration file. Once established on an initial test specimen, the recorded routine can be executed repeatedly on all subsequent specimens of the test sample lot. After a specimen image is analyzed, its statistical data shall be recorded in an associated file and saved to disk. From the file data,
47、 statistical functions may be performed to ascertain such defect geometrical parameters as Mean Size and Size Standard Deviation, in addition to the basic parameters of Percent Damage and Number of Defects, and all these on a per layer basis, where applicable, within the capability of the software p
48、rogram. SAE J2661 Issued MAY2011 Page 5 of 10 5. SETUP AND EVALUATION PROCEDURE 5.1 Specimen Preparation Considerations For a multi-layer coating system to be suitable for imaging analysis evaluation, there must be observable tonal contrast between the coating (or substrate) in the damage sites and
49、the surrounding unaffected coating (or between each layer of the coating system when equipment permits individual layer detection and analysis). Without such contrast, the imaging system will be unable to differentiate between the damaged and original surfaces. As an aid to achieving this, coating systems should be formulated such that the various layers have differing tonal values or tints. When this is not possible, an alternative method
