Crashworthiness Simulation of ET2000 Guardrail Extruder Terminal

What is ET2000? ET2000 is an end treatment for the W-beam guard rails W-beam guard rail, break away wood posts (minimum first 4 of which are secured to foundation tube) and cable anchor system

Objective To develop an accurate simulation of the ET2000 guard rail extruder terminal to predict the crashworthiness during an end on impact When impacted the end treatment causes the W-beam to be flattened and deformed in a controlled manner The flattening process dissipates energy and impacting vehicles are decelerated to a controlled stop

Model of ET2000 Created in HYPERMESH

Cable Anchor System During an end-on impact, the cable is released as soon as the first post breaks and the impact head separates the anchor box from the W-beam and continues down the rail. Without the cable anchor, the tensile forces in the guardrail during a downstream impact would cause a large cantilever bending moment on the weakened first breakaway post that could cause it to fail.

Cable Anchor System

During a downstream redirectional impact the tabs interlock with the slots in the anchor box and provide the needed strength. The cable anchor transfers this tensile load directly to the steel foundation tubes through a cable

ET2000 Guard Rail System

ET2000 Model Wood is a nonlinear orthotropic material Material properties needed to characterize wood are not available Pendulum testing of break away posts are available from roadside hardware testing literature where wood posts are supported in rigid test brackets, or the foundation tube, and the break away force required to break away the wood is measured. Also the post nearly always fails in bending Properties of wood obtained using simulation of these tests are available in literature

Wood Model The middle portion of wood with hole is modeled with isotropic elastic-plastic material model with failure and fully integrated solid element Failure occurs if the effective plastic strain reaches failure strain or when the pressure reaches the tensile failure pressure, then the deviatoric stresses are set to zero The top portion is modeled using an elastic material model with constant stress solid element The lower portion is modeled using kinematic isotropic elastic-plastic material model

ET2000 Model 1988 Chevrolet 2500 pick up truck from National Crash Analysis Center approximately elements Guard rail material is modeled with a piecewise linear isotropic plasticity model Bolt connections are modeled using Constrained Generalized Spot weld by defining normal force at failure and shear force at failure for the bolts (15.9 mm carriage bolts without washers) The system is a 45.7 m long and 25.7 m of the unmodeled portion is represented by a spring with

Contact used Large deformations in crash analysis Automatic contact detects penetration from either side of the element Automatic contact is a two way treatment of contact meaning slave nodes are checked for penetration through master segments and vice versa AUTOMATIC_GENERAL AUTOMATIC_SINGLE_SURFACE AUTOMATIC_SURFACE_TO_SURFACE

AUTOMATIC_GENERAL Shell edge-to-edge or beam-to-beam

AUTOMATIC_GENERAL

AUTOMATIC_SINGLE_SURFACE No master surface. Contact is considered between all parts in the slave list including self contact

AUTOMATIC_SURFACE_TO_ SURFACE The orientation of parts relative each other cannot be predicted in large deformations

Computational Difficulties and Actions to counter them Negative volume in solid element Break away wood post bending and not failing Extruder terminal rotation HRGLASS stiffness Material foam stiffened Fully integrated solid element used to model failure Double precision solver SOFT=0 standard penalty formulation for contact from SOFT=2 segment to segment contact SOFT=0 based on elastic constants and element dimension SOFT=2 based on segment masses and global time step

Simulation

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