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.

1 . A method of modelling 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 method comprising the steps of determining 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; and if said element or layer is determined to be failing by said crush failure mode, calculating a resistance force and assigning said resistance force to said element or layer, wherein said steps of calculating and applying are carried out 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 using said model to output data from which a predicted impact resistance of said structure can be calculated. 
   
   
       2 . A method as claimed in  claim 1  wherein said resistance force is assigned to a portion of said element or layer. 
   
   
       3 . A method as claimed in  claim 2  comprising defining a crush front or barrier and allowing said element or layer to pass through said crush front or barrier whilst being crushed. 
   
   
       4 . A method as claimed in  claim 2  comprising applying said resistance force to individual nodes of the element or layer so that said portion comprises said nodes. 
   
   
       5 . A method as claimed in  claim 4  comprising:
 defining a crush front or barrier and allowing said element or layer to pass through said crush front or barrier whilst being crushed; and   dividing 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 . A method 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 . A method as claimed in  claim 1  comprising determining 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 . A method as claimed in  claim 1  comprising determining 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 . A method as claimed in  claim 1  comprising defining a crush front or barrier and determining said resistance force as a function of a thickness of the element or layer being crushed along the crush front or barrier. 
   
   
       10 . A method as claimed in  claim 1  comprising defining a crush front or barrier and determining said resistance force as a function of an area of contact at the crush front or barrier. 
   
   
       11 . A method 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 . A method as claimed in  claim 11  comprising defining said resistance force as being directly proportional to the area of contact. 
   
   
       13 . A method as claimed in  claim 1  wherein said crushable material is a composite material having a plurality of layers, the method comprising determining said resistance force as a function of the lay-up of said layers. 
   
   
       14 . A method as claimed in  claim 13  comprising determining said resistance force as a function of the order of said layers in the composite. 
   
   
       15 . A method as claimed in  claim 1  comprising determining said resistance force as a function of one or more dynamic parameters relating to the impact. 
   
   
       16 . A method as claimed in  claim 15  comprising determining said resistance force as a function of a velocity and/or an angle at which said element or layer is struck. 
   
   
       17 . A method as claimed in  claim 15  comprising determining said resistance force as a function of an amount of rotation imparted to the element or layer. 
   
   
       18 . A method as claimed in  claim 1  comprising the step of designating a set of finite elements of the structure as being susceptible to failure by said crush failure mode. 
   
   
       19 . A method as claimed in  claim 18  wherein said set is only a subset of all available elements. 
   
   
       20 . A method as claimed in  claim 2  further comprising carrying out finite element calculations on said element or layer in addition to assigning said resistance force to said portion and using 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 . A method as claimed in  claim 20  comprising allocating an element a degraded crush capability for future crush analysis if the results calculated by said finite element analysis are used. 
   
   
       22 . A method as claimed in  claim 1  wherein said finite elements are shell elements. 
   
   
       23 . A method as claimed in  claim 1  wherein said finite elements are solid elements. 
   
   
       24 . A method as claimed in  claim 1  wherein said finite elements are beam elements. 
   
   
       25 . A method as claimed in  claim 1  comprising defining a crush front or barrier and adjusting a relative velocity between an impactor and said element or layer during passage of the crush front or barrier through the element. 
   
   
       26 . A method as claimed in  claim 25  comprising modifying the resistance force along a length of the element in accordance with a predetermined function of the relative velocity. 
   
   
       27 . A method as claimed in  claim 1  comprising defining a crush front or barrier and adjusting an angle of impact between an impactor and said element or layer during passage of the crush front or barrier through the element. 
   
   
       28 . A method as claimed in  claim 27  comprising modifying the resistance force along a length of the element in accordance with a predetermined function of the angle of impact. 
   
   
       29 . A method as claimed in  claim 1  comprising defining a crush front or barrier and specifying a friction of the element or layer with the crush front or barrier. 
   
   
       30 . A method as claimed in  claim 1  comprising specifying material damping coefficients. 
   
   
       31 . A method as claimed in  claim 1  wherein said crushable material comprises a composite material. 
   
   
       32 . A method as claimed in  claim 31  wherein said composite material is a fiber-reinforced composite material. 
   
   
       33 . A method as claimed in  claim 31  wherein said composite material is a carbon-fiber reinforced resin. 
   
   
       34 . A method of modelling 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 method comprising the steps of determining 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; and if said element or layer is determined to be failing by said crush failure mode, assigning to a portion of the structure an ongoing resistance throughout a consumed length of the element or layer, and using said model to output data from which a predicted resistance of said structure can be calculated. 
   
   
       35 . Computer software which, when executed on suitable data processing means, 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, said software determining 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 and if said element is determined to be failing by said crush failure mode, assigning to a portion of the structure an ongoing resistance throughout a consumed length of the element or layer, and using said model to output data from which a predicted impact resistance of said structure can be calculated. 
   
   
       36 . Software for performing finite element modelling comprising software as claimed in  claim 35 . 
   
   
       37 . Software as claimed in  claim 36  wherein said finite element modelling is non-linear. 
   
   
       38 . Software as claimed in  claim 36  wherein said finite element modelling is explicit non-linear. 
   
   
       39 . 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) using said model to out put data from which a predicted impact resistance of said structure can be calculated.   
   
   
       40 . A method of modelling 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 method comprising the steps of using a computer to determine 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; and if said element or layer is determined to be failing by said crush failure mode, assigning to a portion of the structure an ongoing resistance throughout a length of the element or layer, and outputting data from which the predicted impact resistance of said structure can be calculated.