4. Barrier and pole impact configurations

Near-side load path development cannot be validated with a single test setup. The occupant sits close to the struck side, the struck structure is shallow, and the loading geometry changes dramatically depending on what the vehicle hits and at what angle. Three test families dominate near-side evaluation: the moving deformable barrier (MDB), the oblique pole, and sled-based component setups. Each produces a different combination of intrusion pattern, structural loading rate, and restraint timing, and each therefore interrogates a different part of the near-side load path. This chapter explains what each configuration actually applies to the vehicle, how to set it up, and how to read the resulting structural response.

Moving Deformable Barrier: Distributed Side Loading

The MDB configuration represents a striking vehicle. A movable trolley carries a deformable honeycomb or aluminium honeycomb-faced barrier, and the assembly is propelled into the stationary test vehicle at a defined speed and angle. In the widely used side-impact format, the barrier face is 1,500 mm wide and 500 mm high, the trolley mass is approximately 950 kg, and the impact speed is typically 50 km/h with a barrier face angle of 90° or a crab angle introduced by rotating the trolley relative to its travel direction. The barrier face centre is aligned to a specified height above ground — commonly 600 mm — so that the honeycomb engages the door, sill, and lower B-pillar region rather than the glasshouse.

What makes the MDB valuable for load path work is the distributed, compliant loading it applies. The honeycomb crushes progressively, so the door outer panel sees a pressure field rather than a point load, and the load spreads across the door beam, the beltline, and the sill. The near-side load path is therefore exercised in its "realistic" mode: force enters through the door structure, travels through the door beam and hinge/latch attachments into the B-pillar and sill, and then distributes into the floor cross-members and the tunnel. Instrumentation should reflect this: accelerometers on the struck door inner panel, the B-pillar at multiple heights, the sill, the floor tunnel, and the non-struck side sill allow you to trace how much load actually crosses the cabin. A common diagnostic is the ratio of struck-side sill acceleration to far-side sill acceleration; a low ratio indicates the floor is not transferring load efficiently and the near-side structure is being asked to absorb too much energy locally.

Setup discipline matters more than most engineers expect. The trolley guidance must be stiff enough that the barrier does not yaw before contact, the honeycomb must be conditioned to the specified temperature and humidity, and the vehicle must be restrained so that it translates rather than rotates on its suspension. If the vehicle is over-restrained at the far side, the apparent intrusion will be artificially low and the load path will look better than it is.

Oblique Pole: Concentrated, Angled Intrusion

The oblique pole test applies a narrow, rigid load at an angle, and it is the configuration that most directly stresses the near-side load path's ability to resist local punching. A rigid pole of 254 mm diameter is mounted vertically, and the vehicle is propelled into it at an angle — commonly 75° to the vehicle's longitudinal axis in regulatory oblique pole formats, at around 32 km/h — with the pole positioned to strike the driver or front passenger door region. Because the pole is narrow and rigid, the contact patch is small, and the door outer panel, door beam, and B-pillar must resist a highly concentrated force with very little opportunity to spread it.

The load path consequence is a strong vertical and lateral bending demand on the B-pillar and a concentrated shear at the door beam-to-pillar joint. Where the MDB tends to load the sill in bending, the oblique pole tends to drive the B-pillar inward and rearward, and the sill sees a combined bending and torsion. This is why oblique pole results often show B-pillar intrusion that is locally severe even when the overall cabin deformation looks modest. For load path development, the pole test is the check on joint integrity: hinge and latch anchorage, door beam end fittings, and the B-pillar-to-rocker connection are all loaded near their design limits.

Practical setup points: the pole must be rigidly anchored with negligible compliance, the impact angle must be measured from the vehicle centreline and held within a tight tolerance, and the vehicle's lateral drift during impact must be recorded because it changes the effective engagement angle. A useful measurement set includes pole-mounted load cells (where the fixture permits), B-pillar accelerometers at beltline and sill heights, door inner-panel displacement relative to the seat, and a high-speed camera view through the glasshouse to capture the pillar's bending mode.

Sled-Based Near-Side Setups

Sled testing decouples the near-side structure from the full vehicle. A body-in-white section — door, B-pillar, sill, and a portion of the floor — is mounted on a rigid fixture attached to a deceleration sled, and a ram or barrier face is driven into the structure. The sled programme is derived from a full-vehicle acceleration pulse, so the component sees a representative inertial loading while the boundary conditions are controlled and repeatable.

The value of the sled approach is parametric iteration. Because the fixture is reusable and the pulse is programmable, you can change door beam gauge, B-pillar reinforcement grade, or joint design and run a matrix of configurations in days rather than months. The trade-off is boundary condition fidelity: the fixture's stiffness at the sill and floor cut lines must be tuned so that the component does not become either too rigid or too compliant relative to the full body. A practical check is to correlate sled intrusion at the B-pillar against the full-vehicle MDB or pole result at the same location; a mismatch of more than roughly 15–20 mm at beltline height usually indicates the fixture boundary is wrong, not the component.

Choosing and Combining Configurations

The three configurations are complementary rather than alternatives. The MDB establishes whether the distributed load path can carry force across the floor without excessive local intrusion. The oblique pole establishes whether the concentrated load path — pillar, joints, beam end fittings — survives without local collapse. The sled establishes whether a candidate design change actually improves the component before it is committed to a full vehicle. A development programme that runs only the MDB will miss joint-level failures; one that runs only the pole will over-constrain the design toward local stiffness at the expense of floor load sharing.

The figure above maps each configuration to its loading character and its primary diagnostic. Note that the load path arrows differ in kind, not just in direction: the MDB spreads force across the door and sill before it reaches the floor, the pole concentrates force at the pillar and joints, and the sled lets you isolate one of those paths under a controlled pulse. Reading a test result without knowing which path the configuration exercises is the most common source of misdiagnosis in near-side development.

Practical Configuration Checklist

Two engineering cautions apply across all three. First, define your coordinate and sign conventions before instrumentation: lateral intrusion is normally positive toward the vehicle centreline, and every accelerometer and displacement channel should be documented against that convention so that the load path direction is unambiguous in post-test analysis. Second, treat the barrier or pole face condition as a controlled variable — honeycomb temperature and humidity for the MDB, pole surface condition and anchorage stiffness for the oblique pole — because small changes there shift the load path without any change to the vehicle. When a result looks anomalous, check the fixture and the impactor before you check the structure.