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Low Speed Thorax Impact Test Procedure for the HIII 50th Male Dummy (SAE J2779:2022)
This article provides a comprehensive overview of the SAE J2779:2022 recommended practice for performing a low speed thorax impact calibration test on the Hybrid III 50th male Anthropomorphic Test Device (ATD). The procedure is designed to replicate low-energy automotive impacts and ensures the dummy responds consistently within tight deflection and force corridors.
Purpose and Rationale
The standard thorax impact test (6.7 m/s) produces deflections near 68 mm, which is not representative of low-energy collisions. The low speed procedure uses an impact velocity of 3.00 m/s to achieve a deflection target of 25–30 mm, making it suitable for calibrating the dummy under conditions closer to real-world low-severity events. The 2022 reaffirmation updated references, corrected terminology (e.g., “chest flesh” instead of “chest skin”), and changed the deflection filter class from CFC180 to CFC600 to align with SAE J2856 and the latest SAE J211-1 recommendations.
🔍 The low speed test complements the standard high-speed thorax calibration; both are essential for ensuring dummy performance across the full crash severity spectrum.
Test Setup and Calibration Procedure
Probe and Fixture Specifications
The impact fixture must meet precise geometric and mass requirements, as summarized below:
| Parameter | Value |
|---|---|
| Probe mass (including instrumentation and ⅓ of cable) | 23.36 ± 0.02 kg (51.5 ± 0.05 lb) |
| Probe diameter | 152.4 ± 0.25 mm (6.0 ± 0.01 in) |
| Impact face edge radius | 12.7 ± 0.3 mm (0.50 ± 0.01 in) |
| Impact velocity | 3.00 ± 0.06 m/s |
| Pendulum force filter class | CFC180 (phaseless) |
| Chest deflection filter class | CFC600 (phaseless) |
Dummy Preparation and Positioning
- Dummy assembly: Use the complete dummy with shirt and pants (no shoes). Remove the chest flesh to inspect the thorax assembly for cracks, worn damping material, and proper torque of spine cables (1.2–1.4 N·m).
- Soak conditions: Condition the dummy at 20.6–22.2°C (69–72°F) and 10–70% relative humidity for at least four hours before testing. Maintain these conditions throughout the test.
- Positioning: Seat the dummy (without chest flesh but with pants) on a clean, dry steel surface. Level the ribs longitudinally and laterally within ±0.5°, and set the pelvis angle to 13° ± 2°. The midsagittal plane must be vertical ±1° and parallel to the probe centerline within 2°.
- Probe alignment: Center the probe on the midsagittal plane within 3 ± 0.25 mm. Align the probe longitudinal centerline 12.7 ± 1 mm below the horizontal centerline of the No. 3 rib, within 0.5° of horizontal.
- Reference measurements: Record distances from the thoracic spine and lower neck bracket to fixed references. After installing the chest flesh and shirt, reposition the dummy to match these references, ensuring consistent impact location.
⚠️ Common mistakes: using incorrect probe mass or edge radius, failing to level the ribs, and forgetting to shift the dummy rearward to account for chest flesh thickness when using a cable-suspended probe.
Impact and Data Acquisition
The test probe must guide with no significant lateral, vertical, or rotational motion during impact. Time-zero is defined as initial contact between the probe and chest flesh. Wait at least 30 minutes between successive tests on the same thorax to allow the rib damping material to recover.
Performance Specifications and Design Insights
The calibration is considered successful if the following metrics are achieved:
| Parameter | Requirement |
|---|---|
| Maximum sternum-to-spine deflection | 21.5 – 26.5 mm |
| Maximum force applied to thorax | 2.38 – 2.73 kN |
| Internal hysteresis ratio | 60 – 75% |
The hysteresis ratio is defined as the area between the loading and unloading portions of the force-deflection curve divided by the area under the loading portion. This ratio reflects the dummy’s energy absorption characteristics and is critical for ensuring biofidelity in low-speed events.
Engineering design insight: The low speed test intentionally uses a tighter deflection corridor (≈25 mm) than the standard high-speed test (≈68 mm). This requires precise setup and a higher‑order filter (CFC600) for chest deflection to preserve signal fidelity at lower impact velocities. The test’s sensitivity to dummy positioning means that even minor deviations in pelvis angle or rib leveling can push results outside the specification.
Frequently Asked Questions
1. Why was the filter class for chest deflection changed from CFC180 to CFC600?
With lower impact speeds, chest deflection signals contain higher‑frequency components that require a wider bandwidth to avoid attenuation. The change aligns with SAE J2856 and ensures the deflection measurement captures the true chest response in low‑energy impacts.
2. Do I need to remove the chest flesh during every test?
Yes, at least during the initial setup. Removing the chest flesh allows visual inspection of the ribs, damping material, and transducer. It also enables accurate reference measurements before reinstalling the chest flesh and clothing for the impact.
3. How long should I wait between successive tests on the same dummy?
At least 30 minutes. This recovery period allows the rib damping material to return to its initial state, ensuring consistent hysteresis and deflection results.
4. What are the most frequent reasons for calibration failure?
Common failures include incorrect probe mass/edge radius, improper pelvis angle or rib leveling, using CFC180 instead of CFC600 for chest deflection, and not accounting for chest flesh thickness when setting probe position in cable‑suspended setups.
🛠️ Following the procedure precisely and verifying each setup condition against the standard will significantly improve calibration repeatability and pass rates.
