SAE-J89-2007.pdf

_ 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 therefrom, 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 © 2007 SAE International All rights reserved. No part of this publication may 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: 724-776-4970 (outside USA) Fax: 724-776-0790 Email: CustomerServicesae.org SAE WEB ADDRESS: http:/www.sae.org J89 REV. APR2007 SURFACE VEHICLE RECOMMENDED PRACTICE Issued 1973-07 Revised 2007-04 Superseding J89 JUN1995 Dynamic Cushioning Performance Criteria for Snowmobile Seats RATIONALE Five year review. Document format previously updated. Changes: 1.1 Purpose: Deleted obsolete reference to SAE J89a 1.2 Contents: Added Section 6 Notes 2.1.1 SAE Publications; Corrected title of J33 4.2.5 Removed abbreviation; Changed h to hours 1. SCOPE This SAE Recommended Practice encompasses the significant factors which determine the effectiveness of a seat system in limiting spinal injury during vertical impacts between the rider and the snowmobile seat system. The document is intended to provide a tool for the development of safer snowmobile seats. It is recognized that the seat is only a portion of the entire vehicle protective suspension system. It is, however, usually required that the seat serve as added protection to the suspension system, since the latter may “bottom out“ during a severe impact. The term “seat“ refers to the occupant-supporting system not normally considered part of the vehicle suspension or frame system. In some cases, it may include more than the foam cushion. This document provides the minimum requirements for performance of a general seat system, and a description of specific means of evaluating the shock-absorbing characteristics of foam seat cushions using a specific testing procedure and a companion seat evaluation chart. The test input and means of interpreting the results are unique to the seats of typical recreational snowmobiles. Therefore, this document is to be used for snowmobile seats only and is not to be used to evaluate seats of any other type of vehicle. In addition, it should not be applied to seats of snow vehicles of significantly different design, dimensions, construction, or intended usage from the typical recreational snowmobile illustrated in SAE J33. 1.1 Purpose The purpose of this document is to facilitate the development of seats used on snowmobiles to minimize occupant spinal injury during impacts of: a. The occupant on the snowmobile seat b. The snowmobile and seat on the occupant Operators and passengers of snowmobiles can be subjected to high levels of impact with the snowmobile seat under riding conditions. This document was developed to identify the cushioning properties of snowmobile seats. -,-,- SAE J89 Revised APR2007 - 2 - 1.2 Contents Section 1Scope Section 2Reference Section 3Definitions Section 4Testing Method Section 5Evaluation Section 6Notes 2. REFERENCE 2.1 Applicable Publication The following publication forms a part of this specification to the extent specified herein. The latest issue of SAE publication shall apply. 2.1.1 SAE Publication Available from SAE, 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 J33 Definitions for Snowmobiles 3. DEFINITIONS 3.1 Snowmobile Seat The seat includes the cover, energy-absorbing materials, and substrates (if any). 3.2 Baseline The baseline is the starting reference plane of the seat from which total penetration is determined. It is taken as the top plane of the seat at the fore-aft position designated for the snowmobile occupant(s). 3.3 G Symbol for the dimensionless ratio of any acceleration to the acceleration of gravity. 3.4 tp Time duration impact to peak deceleration, in milliseconds. 3.5 th Time duration from impact to 1/2 value of peak deceleration, in milliseconds. 4. DYNAMIC CUSHIONING TESTING METHOD 4.1 Scope This procedure provides a uniform method for measuring, with a high degree of reproducibility, dynamic cushioning properties such as the deceleration-time history profile of a standard buttocks form (“missile“) impacting seat test specimens. The results from this testing method can be related to the performance requirements necessary to limit spinal injury to snowmobile riders and passengers. SAE J89 Revised APR2007 - 3 - 4.2 Apparatus 4.2.1 Testing Machine Any design of dynamic testing apparatus will suffice when the following criteria are met. See Figure 1. 4.2.1.1 The weighted missile can be held in readiness for impact, released upon command, and guided to the point of impact. 4.2.1.2 The test specimen should be supported on a foundation which under impact will not deflect more than 1% of the thickness of the specimen. 4.2.1.3 The deceleration-time profile, as illustrated in Figure 2, can be read out and recorded on an instrument, such as an oscilloscope, starting at the time of initial contact of the missile on the seat. FIGURE 1 - DYNAMIC TESTING APPARATUS SAE J89 Revised APR2007 - 4 - FIGURE 2 - TYPICAL G-TIME TRACE 4.2.2 Sending Devices 4.2.2.1 The missile shall be equipped with an accelerometer system which shall be capable of measuring single impacts of short duration (less than 0.105 s) in the 5 to 100 g range with an accuracy of ±2% throughout the duration of the pulse. 4.2.2.2 A penetration measuring device or some other means is required to determine the exact starting time of the penetration. A velocity measuring device shall be used for measuring the impacting velocity of the missile if the missile is not totally free to fall under the influence of gravity. 4.2.3 Missile The missile shall be a rigid segment of a hemisphere, the sphere having a radius of 245 mm (9.65 in) and the segment having a radius of 178 mm (7 in). (See Figure 3). The top surface of the missile must be designed to accommodate weights to provide total missile mass capability of 90.7 kg (200 lb). FIGURE 3 - SEAT IMPACT FORM 4.2.4 Recording Equipment The acceleration-time recording equipment should be capable of recording impacts compatible with the accuracy of the accelerometer. Some type of triggering device will be necessary for the recording device. -,-,- SAE J89 Revised APR2007 - 5 - 4.2.5 Test Specimen Any seating system, or component, for which dynamic cushioning data is desired. The number of specimens tested as a sample can vary widely depending upon the intended use of the data. It is recommended that at least three specimens be tested for each set of conditions. The specimens shall be conditioned at 21 °C ± 6 °C (70 °F ± 10 °F) for a minimum of 8 hours prior to testing. 4.3 Procedure 4.3.1 Prewarm the recording equipment as recommended by the manufacturer. 4.3.2 Place the test specimen in position under the missile such that the designated seating position coincides with the center of the missile. Mass of the missile shall total 90.7 kg (200 lb). 4.3.3 Determine the baseline by contacting the specimen with the missile and adjust the recording apparatus to read zero penetration. 4.3.4 Set the missile propelling mechanism at a position to obtain the desired impact velocity of 3.15 m/s (124 in/s) equivalent to 500 mm (20 in) free fall at the impact surface of the specimen. 4.3.5 Calibrate the G-time recorder according to the recommended procedure of the manufacturer. 4.3.6 Release the missile and record the acceleration-time profile using the recommended procedures of the equipment manufacturer. Five consecutive strikes shall be made at 2 min intervals on the same impact area. 4.3.7 Each passenger's designated seating position (if the snowmobile is designed for passengers) and each designated seating position of the operator shall be tested. 5. EVALUATION The following procedure shall be applied to each designated seating position. 5.1 Data Using the deceleration time trace from the fifth impact on each of the three specimens, record the peak deceleration (point C), the time from impact to peak deceleration (point tp), and the time from impact to 1/2 peak deceleration (point th) for the designated seating position. Calculate and record the average value for C, tp, and th and, using these average values, calculate and record the percent distortion using Equation 1: %100 t tt2 distortion% p ph × = (Eq. 1) 5.2 Chart Usage On the seat evaluation chart (Figure 4), plot the previous calculated average values of peak deceleration (C) and time from impact to peak deceleration (tp). If this point lies above the 90% distortion line, the seat fails. If the point lies below the 30% distortion line, the seat passes. If the data point lies within the region of 30 to 90% distortion, then the point must be evaluated with respect to its calculated percent distortion. If the data point lies above its distortion value, the seat fails. If the data point lies below its distortion value, the seat passes. As an example of the previous procedure: tp = 40 ms th = 30 ms Gmax = 35 g SAE J89 Revised APR2007 - 6 - Then see Equation 2: %50%100 40 40)30(2 distortion%=× = (Eq. 2) Plotting 35 g at 40 ms on Figure 4 indicates the data point falls above its distortion curve. Therefore, the seat fails. If Gmax had been below 35 g, the seat would have passed. NOTE: The particular procedure described previously is not applicable to seats giving rise to deceleration pulses of shapes radically different from that shown in Figure 2. The specific method of seat evaluation described in this section is generally applicable to foam seat cushions. FIGURE 4 - SEAT EVALUATION CHART 6. NOTES 6.1 Marginal Indicia The change bar (l) located in the left margin is for the convenience of the user in locating areas where technical revisions have been made to the previous issue of the report. An (R) symbol to the left of the document title indicates a complete revision of the report. PREPARED BY THE SAE SNOWMOBILE COMMITTEE -,-,-