01Convert speed to height, and write the arithmetic down
The conversion is velocity squared over twice gravity, applied to the vertical share a rut actually produces. At 6 m/s the equivalent drop lands between 0.3 and 0.4 m; at 15 m/s between 1.3 and 1.6 m; at 22 m/s between 2.2 and 2.5 m. Those steps are not evenly spaced, which matters when test speeds get chosen.
Height is a bookkeeping unit, not a verdict. It puts different speeds on one ruler so they can be ranked, while the call itself still rests on energy and on how deep the surface is marked. The conversion share drifts with speed too: at the low end the rut dominates and the vertical portion is large, while at the high end the box stays airborne longer and lands at a more random angle.
02Throw distance scatters the landing, and the scatter picks the edge
Horizontal throw runs 2 to 15 m, set by release speed and tailgate height. Ten repeats at one station can spread landing points across 1 to 3 m, and that spread decides whether an edge or a face takes the hit, which decides where the abrasion mark appears and how deep it reads.
Fix release height so distance varies only with speed. Mark the floor in zones and log the contact area zone by zone. Without that, ten tosses look like ten samples when seven of them landed on the same corner, and every conclusion after that rests on a sample size of one. Averages drawn from that are a single reading wearing a mean.
03One to six rolls, a different edge each time
A tossed case keeps rolling after it lands, one to six times depending on attitude and centre of gravity. Rolling adds little energy. What it does is spread impact across several edges and smear a single abrasion line into a patch, which is exactly where the deepest point becomes easy to overlook during inspection, so a grid sweep comes before any measurement.
Count contact events rather than revolutions. One roll can produce a single solid contact, or two scrapes along the same edge. An entry reading four contacts, three on edges and one on a face, is worth more than one reading four rolls, and it is the version that still reconciles with a cumulative abrasion figure later on, edge by edge.
04A 20–120 mm rut sets how long the contact lasts
Rut height between 20 and 120 mm changes both airborne time and contact time. A tall rut throws the box higher, so it arrives faster, but contact compresses to 0.1–0.2 s and the impulse concentrates on a small area. A shallow rut keeps the box skimming, with contact lasting 0.5–0.8 s at a lower peak. Each setting leaves a different mark.
Both damage the case, in different places. Short contact loads a small patch and leaves a deep narrow dent. Long contact wears the whole bottom edge, shallow but wide. Run the station at two rut heights; a single setting cannot claim to cover a road profile, and the second run is usually where an edge finally gives way.
05Book the energy per toss, then check three limits
Energy per toss runs 30 to 350 N·m, estimated as half the mass times velocity squared at full load, with the load treated as evenly distributed rather than shifting in flight. Twenty tosses can total more than one high drop, yet the damage spreads across different edges, which is why a single drop height cannot stand in for a toss run.
Three limits close the run: abrasion depth no more than 1.2 mm, no visible cracking at latches or seats, no dent through the wall at an edge. Break any one and the run stops, since extra tosses add nothing but time. Footage shows the throw and the landing; release rests on the energy log and the measured mark depth.
| Simulated road speed | 5–22 m/s horizontal |
|---|---|
| Equivalent drop height | 0.3–2.5 m |
| Throw distance | 2–15 m |
| Roll count | 1–6 rolls |
| Rut height | 20–120 mm |
| Single contact duration | 0.1–0.8 s |
| Abrasion mark depth | 0.1–1.2 mm |
| Energy per toss | 30–350 N·m |
FAQ
Why not just count how many times it was thrown?
Same count, different speed, several times the energy. Ten tosses at 5 m/s and ten at 22 m/s are not in the same order of magnitude, and they fail differently. Book the energy; the count is only a tally.
Does the equivalent height mean it fell from that height?
It is a ruler for comparing speeds, nothing more. Landing attitude, contact area and contact duration all differ. Use the height to rank runs, never as the verdict.
How do you count rolls without double-counting?
Count effective contact events, not revolutions. One roll may give a single contact or two scrapes along an edge, so log edges and faces separately.
Where does the 1.2 mm abrasion limit come from?
Worked back from wall thickness and rib position: at 1.2 mm the load-bearing section of the bottom rib still has margin, and beyond it the structure is reached. It is this station's stop line, not a general standard.
