Crush modelling

Abstract

A method of determining the impact resistance of a structure including a crushable material comprises the steps of determining for one or more layers of a finite element of the material during an impact whether the element or layer thereof is to be treated as failing by crushing. If the element or layer is determined to fail by crushing, a load-bearing portion of the structure is defined and the load-bearing portion is treated for the purpose of subsequent calculations as exhibiting an ongoing resistance.

What is claimed is: 
     
         1 . A data processing system which models the behaviour of a structure during an impact, said structure incorporating a material which can fail through a crush failure mode, whereby said material is continuously consumed by disintegrating into debris, the system comprising:
 a computer that: (i) determines for one or more layers of a finite element of said material during an impact whether said element or layer thereof is failing by said crush failure mode; (ii) if said element or layer is determined to be failing by said crush failure mode, said computer calculates a resistance force and assigns said resistance force to said element or layer one or more times such that a resistance force is assigned to said element or layer for as long as the length of the element or layer is being reduced by said crush failure mode; and (iii) outputs data from which a predicted impact resistance of said structure can be calculated.   
     
     
         2 . The system as claimed in  claim 1  wherein said resistance force is assigned to a portion of said element or layer. 
     
     
         3 . The system as claimed in  claim 2 , wherein said computer defines a crush front or barrier and allows said element or layer to pass through said crush front or barrier whilst being crushed. 
     
     
         4 . The system as claimed in  claim 2 , wherein said computer applies said resistance force to individual nodes of the element or layer so that said portion comprises said nodes. 
     
     
         5 . The system as claimed in  claim 4 , wherein said computer:
 defines a crush front or barrier and allows said element or layer to pass through said crush front or barrier whilst being crushed; and   divides said resistance force by allocating a first percentage of said resistance force to a first set of nodes that have passed through the crush front or barrier and a second percentage of said resistance force to a second set of nodes that have not passed through the crush front or barrier, wherein said first and second percentages are calculated either as a function of the area of the element or layer that has passed through the crush front or barrier or as a function of the distance that said element or layer has passed through the crush front or barrier.   
     
     
         6 . The system as claimed in  claim 5  wherein said first percentage is the percentage of the area of the element or layer that has passed through the crush front or barrier or the percentage of the length of the element or layer normal to the crush front or barrier that has passed through the crush front or barrier. 
     
     
         7 . The system as claimed in  claim 1 , wherein said computer determines whether the element or layer is failing by said crush failure mode by determining whether an impactor barrier has physically encroached into a space allocated to said element or layer. 
     
     
         8 . The system as claimed in  claim 1 , wherein said computer determines whether the element or layer is failing by said crush failure mode by calculating the stress or strain on the element or layer and comparing said stress or strain with a threshold failure value. 
     
     
         9 . The system as claimed in  claim 1 , wherein said computer defines a crush front or barrier and determines said resistance force as a function of a thickness of the element or layer being crushed along the crush front or barrier. 
     
     
         10 . The system as claimed in  claim 1 , wherein said computer defines a crush front or barrier and determines said resistance force as a function of an area of contact at the crush front or barrier. 
     
     
         11 . The system as claimed in  claim 10 , wherein for a given element said resistance force has an actual value which is a constant function of the area of contact. 
     
     
         12 . The system as claimed in  claim 11 , wherein said computer defines said resistance force as being directly proportional to the area of contact. 
     
     
         13 . The system as claimed in  claim 1  wherein said crushable material is a composite material having a plurality of layers, wherein said computer determines said resistance force as a function of the lay-up of said layers. 
     
     
         14 . The system as claimed in  claim 13 , wherein said computer determines said resistance force as a function of the order of said layers in the composite. 
     
     
         15 . The system as claimed in  claim 1 , wherein said computer determines said resistance force as a function of one or more dynamic parameters relating to the impact. 
     
     
         16 . The system as claimed in  claim 15 , wherein said computer determines said resistance force as a function of a velocity and/or an angle at which said element or layer is struck. 
     
     
         17 . The system as claimed in  claim 15 , wherein said computer determines said resistance force as a function of an amount of rotation imparted to the element or layer. 
     
     
         18 . The system as claimed in  claim 1 , wherein said computer designates a set of finite elements of the. 
     
     
         19 . The system as claimed in  claim 18  wherein said set is only a subset of all available elements. 
     
     
         20 . The system as claimed in  claim 2 , wherein said computer carries out finite element calculations on said element or layer in addition to assigning said resistance force to said portion and uses the results calculated by said finite element calculations in subsequent analysis instead of said resistance force if said results indicate the element or layer is not failing by said crush failure mode. 
     
     
         21 . The system as claimed in  claim 20 , wherein said computer allocates an element a degraded crush capability for future crush analysis if the results calculated by said finite element analysis are used. 
     
     
         22 . The system as claimed in  claim 1  wherein said finite elements are shell elements. 
     
     
         23 . The system as claimed in  claim 1  wherein said finite elements are solid elements. 
     
     
         24 . The system as claimed in  claim 1  wherein said finite elements are beam elements. 
     
     
         25 . The system as claimed in  claim 1 , wherein said computer defines a crush front or barrier and adjusts a relative velocity between an impactor and said element or layer during passage of the crush front or barrier through the element. 
     
     
         26 . The system as claimed in  claim 25 , wherein said computer modifies the resistance force along a length of the element in accordance with a predetermined function of the relative velocity. 
     
     
         27 . The system as claimed in  claim 1 , wherein said computer defines a crush front or barrier and adjusts an angle of impact between an impactor and said element or layer during passage of the crush front or barrier through the element. 
     
     
         28 . The system as claimed in  claim 27 , wherein said computer modifies the resistance force along a length of the element in accordance with a predetermined function of the angle of impact. 
     
     
         29 . The system as claimed in  claim 1 , wherein said computer defines a crush front or barrier and specifies a friction of the element or layer with the crush front or barrier. 
     
     
         30 . The system as claimed in  claim 1 , wherein said computer specifies material damping coefficients. 
     
     
         31 . The system as claimed in  claim 1  wherein said crushable material comprises a composite material. 
     
     
         32 . The system as claimed in  claim 31  wherein said composite material is a fiber-reinforced composite material. 
     
     
         33 . The system as claimed in  claim 31  wherein said composite material is a carbon-fiber reinforced resin. 
     
     
         34 . A data processing system which models the behaviour of a structure during an impact comprising:
 a computer that: (i) determines for one or more layers of a finite element of a material during said impact whether said element or layer thereof is failing by a crush failure mode whereby said material is continuously consumed by disintegrating into debris; (ii) if said element is determined to be failing by said crush failure mode pursuant to (i) above, said computer assigns to a portion of said structure an ongoing resistance throughout a consumed length of the element or layer; and (iii) out puts data from which a predicted impact resistance of said structure can be calculated.   
     
     
         35 . A data processing system which models the behaviour of a structure during an impact, said structure incorporating a material which can fail through a crush failure mode whereby said material is continuously consumed by disintegrating into debris, the system comprising:
 a computer that: (i) determines for one or more layers of a finite element of said material during said impact whether said element or layer thereof is failing by said crush failure mode; (ii) if said element or layer is determined to be failing by said crush failure mode, said computer assigns to a portion of the structure an ongoing resistance throughout a length of the element or layer, and (iii) outputs data from which the predicted impact resistance of said structure can be calculated.