Shockwave Mitigating, Energy Absorbing Sandwich Belly-Plates (CRBP) for Ground Vehicles
Land mine and IED blasts are the cause of many deaths and critical injuries to civilians as well as military personnel operating in areas of conflict – present and historic. Vehicles in these conflict zones need underbody protection.
ABBS have progressed with the design and demonstration of a new belly plate design based on a flat sandwich structure which ensures that the whole volume of the belly plate is involved in absorbing energy, reducing local deformation levels and enabling fitting the design to lightweight commercial vehicles with low ground clearance whilst also avoiding the negative effects of raised centre of mass on military types.
The ABBS energy absorbing sandwich belly plate assembly minimises faceplate deformation and impulse transfer, whilst maximising load transference between the steel and composite structural elements: the CRBP design seeks to maximise energy-absorption and shock-wave attenuation.
Jig testing has demonstrated CRBP performance (and test jig response) over 4kg and 6kg TNT-equivalent buried charges, set in unprepared ground.
The test jig had an all-up weight of 1.8 Tonnes.
- The 4kg (TE) test demonstrated survival of the CRBP, with 50mm (2”) deflection in its upper face (75mm / 3” indentation into its faceplate), with the test jig thrown 4 metres (12 feet).
- The 6kg (TE) test caused some fracturing of the CRBP, with 230mm (9”) deflection in its upper face, with the test jig thrown 20 metres (60 feet).
These results contrast with the CRBP fracture (and vehicle loss) seen in earlier baseline testing of a vehicle test rig over a 6kg (TE) charge.
ABBS consider the 4kg (TE) under-body threat is effectively addressed by the CRBP, with a blast seat then addressing the effects of global acceleration and slam-down on the seat occupant.
The technology has been demonstrated in full scale vehicle firings in the UK:
- a Snatch Land Rover subjected to a 6kg mine.
- a Toyota Hilux™ tested with a 4kg mine fully to the Dstl/WP53308 1.0 standard, equivalent to NATO AEP-55 STANAG 4569.
Hence, the technology is judged to be at TRL6.
CRBP Design Overview
The ABBS CRBP is made up of the following elements which have been specifically designed for testing on the profile of a Toyota HiLux.
- Steel Armour Faceplate
- Energy Absorbing Core
- Steel Armour Cover Plate
Isometric views of the CRBP – note the rectangular aperture (cut-out) in the Cover plate towards the front of the assembly, to accommodate the gearbox of the HiLux vehicle.
Test Jig design
A steel frame test jig was fabricated in structural steel, to provide a support interface to the CRBP replicating the chassis rails of a Toyota HiLux vehicle
The test jig frame provided an all-up weight (jig including CRBP) of 1.8 Tonnes.
For these tests, the CRBP has a depth of approximately 3″ (75mm) and weighs approximately 400kg.
Ground Condition for Blast Tests
The test jig provided a 230mm (9 inches) ground clearance below the faceplate of the CRBP.
Each threat charge was buried 100mm (4”) beneath the ground surface.
The test pit was sampled, with the sand/soil/gravel media having a nominal density of 1,800 kg m-3
Test #1: 1.8 Tonne Test Jig over 4kg (TE) charge
The objective of this test was to demonstrate the effectiveness of a CRBP test assembly over a 4kg TNT-equivalent (TE) threat charge, and to establish the jump height of a light-weight (1.8 Tonne) test jig over a DSTL Protection Level D1 under-body threat.
The detonation resulted in a jump height of approximately 4 metres.
Test #1: Analysis
Inspection of the CRBP hardware revealed peak deformation of 75mm (3”) in the Faceplate and peak deformation of 50mm (2”) in the Cover plate
No further damage was evident in the Faceplate.
With the CRBP dismantled and lowered from the test jig, the Cover Plate was clearly visible (showing no penetration nor cracking), and very uniform distribution of the deformation.
ABBS consider this test to have shown the 4kg (TE) under-body threat was effectively addressed by the CRBP.
Given the 4-metre (12 feet) jump height seen with this light-weight 1.8 tonne test jig, an energy-absorbing (stroking) blast seat can be used to address the associated effects of global acceleration and slam-down on the seat occupant.
Test #2: 1.8 Tonne Test Jig over 6kg (TE) charge
The objective of this test was to demonstrate the effectiveness of a CRBP test assembly over a 6kg TNT-equivalent (TE) threat charge, and to establish the jump height of a light-weight (1.8 Tonne) test jig over a STANAG level M2b under-body threat (equivalent to Dstl Protection Level D2)
Test #2: Analysis
On detonation of the 6kg (TE) under-body charge, the test jig was thrown c.20 metres vertically.
The blast seat mounted atop the rig was seen to fully stroke within an initial 40 msec period.
Inspection of the CRBP hardware revealed fracture of the Faceplate and localised cracking towards the front of the Cover Plate (around the existing rectangular aperture for the HiLux gearbox), with Cover Plate deformation of 23cm (9”)
The Faceplate was found to fracture laterally, across the centre of the CRBP
Whilst this test established the design limitation of the light-weight CRBP on a light-weight test jig, the ABBS VGAMTM active countermeasure system can be added to a lightweight vehicle to mitigate the global acceleration, and enable a lightweight vehicle to remain near the ground
Comparison with Preliminary CRBP Baseline Test – 6kg (TE) on Toyota HiLux
This preliminary CRBP design was based upon earlier ABBS work from 2017-18, optimised for minimum mass, and modelled using finite-element analysis (FEA); a key output from this test was to calibrate the design model factors used within this FEA design model.
Whilst on detonation, the HiLux was only thrown approximately 4 metres into the air, the under-body blast was seen to penetrate the vehicle cab, indicating failure of the CRBP.
Inspection of the Test Rig showed vehicle loss, with longitudinal fracture of the preliminary CRBP Faceplate and Cover Plate.
By comparison, the latest tests have shown big improvements in the performance of the current version of the CRBP which has proven to effectively address the 4kg (TE) under-body threat by maximising energy-absorption and shock-wave attenuation.
As can be seen in the photographs to the right, even following the 6kg (TE) test, the revised CRBP was much improved over the baseline test and withstood the effects of the blast with no penetration through the upper layers.
Result of 6kg (TE) Test on Revised CRBP April 2021
The Future of the ABBS Belly Plate
We are already seeing an increase in interest in the type of passive protection against blast threats that the revised CRBP can provide.
Not only can this be used as a flat belly plate to provide protection for civilians and aid agencies working in former war zones, but it is also potentially suitable as an upgrade for existing MRAP V-hulls.
As an upgrade, to V-hulls, the energy absorbing technologies of the CRBP can mitigate the initial peak shockwave loads and increase blast capability to a level above what exists already. This would result in only a 50mm decrease in ground clearance and fairly insignificant weight addition.
Shock transfer into the main vehicle structure should be reduced as well as making it less likely that belly plate failure will occur due to the peak loading.
Watch out for the results of our further testing.