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SAE J2878-2022: Low Speed Thorax Impact Test for the HIII5F Dummy
This SAE Recommended Practice establishes a procedure for performing a low-speed thorax impact test on the Hybrid III Small Female (HIII5F) anthropomorphic test device (ATD). The test addresses the industry need for a certification method that produces chest deflections representative of those observed in current full-vehicle frontal impacts. By using a 3.0 m/s impact speed, J2878 delivers more realistic loading conditions compared to the standard 6.7 m/s thorax test, which historically produced deflections greater than those seen in production vehicles.
The Rationale Behind the Low-Speed Approach
The standard thorax certification test for the HIII5F dummy, performed at 6.7 m/s, yields peak chest deflections that exceed those measured in modern frontal impact tests. To better correlate with real-world vehicle performance, the low-speed procedure was introduced. The impact speed of 3.0 m/s aligns with the approach already defined in SAE J2779 for the HIII50M dummy. This harmonization across dummy sizes allows for consistent evaluation of thorax response under frontal loading conditions.
🛠️ Design Insight: The low-speed test (3.0 m/s) was developed because the standard 6.7 m/s thorax test produced chest deflections exceeding those seen in modern vehicle frontal impacts. Using a lower speed gives more representative certification results.
Certification Procedure Key Requirements
The J2878 procedure specifies detailed requirements for dummy preparation, test setup, environmental conditioning, and impactor configuration. The following table summarizes the critical parameters:
| Parameter | Requirement |
|---|---|
| Impact speed | 3.00 ± 0.05 m/s |
| Probe mass (including instrumentation) | 13.97 ± 0.023 kg (30.80 ± 0.05 lb) |
| Probe diameter | 152.4 ± 0.25 mm (6.0 ± 0.01 in) |
| Probe face edge radius | 12.7 ± 0.3 mm (0.5 ± 0.01 in) |
| Environmental temperature (soak and test) | 20.6 to 22.2 °C (69 to 72 °F) |
| Relative humidity | 10 to 70% |
| Dummy conditioning duration | At least 4 hours |
| Spine cable torque | 1.13 – 1.36 N·m (10 – 12 in-lbf) |
| Probe alignment relative to midsagittal plane | Within ± 3 mm centered, ≤ 2° parallel |
| Probe vertical position (below No. 3 rib centerline) | 12.7 ± 1 mm |
| Pelvis angle | 7 ± 2° |
The dummy must be prepared without shoes, with the chest flesh removed during initial setup to allow visual inspection and reference measurements. The arms are positioned horizontally and parallel to the midsagittal plane. Neck bracket index marks must be aligned to zero. The ribs must be leveled longitudinally and laterally within ± 0.5° relative to the No. 3 rib. After setup, the chest flesh and shirt are reinstalled, and the dummy is repositioned using reference measurements taken from locations such as the thoracic spine and lower neck bracket.
Data acquisition follows SAE J211/1 requirements, with pendulum force filtered to Channel Class 180 and chest deflection to Channel Class 600 (both phaseless). The chest displacement transducer must be calibrated per SAE J2517 (September 2006 or later).
⚠️ Common Mistake: Improper dummy conditioning can significantly affect test results. Ensure the dummy is soaked at the specified temperature and humidity for at least four hours before testing. Also, do not forget to remove the chest flesh during initial reference setup, and torque the spine cables correctly to avoid variations in deflections.
Performance Specifications and Design Insights
The J2878 procedure defines three key performance criteria for the thorax response:
- Maximum sternum-to-spine deflection: between –21.8 mm and –17.4 mm (compression).
- Maximum impact force: between –2.07 kN and –1.78 kN.
- Internal hysteresis ratio: greater than 65% but less than 79% (ratio of energy returned to energy absorbed).
The hysteresis corridor upper limit was revised from 72% to 79% in the 2022 reaffirmation to better reflect the damping characteristics of the dummy thorax. The test is designed to be performed on a fully assembled dummy including t-shirt and pants, and the same thorax may be retested after a minimum 30-minute recovery period.
This low-speed certification procedure provides a more relevant benchmark for evaluating the HIII5F dummy’s thorax in frontal impact scenarios, supporting both compliance testing and research applications.
Frequently Asked Questions (FAQs)
Why was a low-speed thorax test necessary for the HIII5F dummy?
The standard 6.7 m/s thorax impact test produced chest deflections that were higher than those observed in actual full-vehicle frontal crash tests. The low-speed procedure at 3.0 m/s better correlates with modern vehicle responses and aligns with the approach used for the HIII50M dummy.
How does the J2878 test setup differ from the standard thorax impact test?
The primary difference is the reduced impact speed (3.0 m/s vs. 6.7 m/s). The impactor mass, geometry, and dummy preparation are similar, but J2878 emphasizes more stringent alignment tolerances and specific reference measurements to ensure reproducibility when the chest flesh is installed.
What are the critical alignment tolerances in the procedure?
The probe must be centered on the midsagittal plane within ±3 mm and parallel within 2°. The vertical height of the probe centerline is set 12.7 ± 1 mm below the No. 3 rib horizontal centerline. The pelvis angle must be 7 ± 2°, and ribs must be leveled within ±0.5°.
What performance criteria must the dummy meet in this test?
Acceptable performance requires a chest deflection between –21.8 and –17.4 mm, a force between –2.07 and –1.78 kN, and a hysteresis ratio between 65% and 79%. These limits ensure the dummy’s thorax behaves within a representative and repeatable corridor.
