Application Dynfold

Application Dynfold

Dynfold is designed to prepare input files for simulation based airbag folding process.

Typical physical airbag folding process is done in 4-5 steps. Dynfold user interface is

designed to setup one step at a time. Often the deformed shape at the end of one folding step is used as a starting mesh for the next step.

The airbag model is expected to have nodes, elements, part, section and material defined before using this interface.

The physical folding process is generally of the following form:

a. hold the bag in position while being folded

b. clamp a portion of the bag to a folding tool

c. Apply motion to the tool in translational direction or rotational direction or combination of both.

At present 5 folding tools are supported. Loadmesh, SPC, BPMF(BOX), Stitching and TUCK.Loadmesh can be any folding tool that is meshed. Typically these tools can be a flat

plane, circular roller , flat roller or any folding tool that is used in the physical folding process. For this type of tool, a tool mesh is expected to be defined with nodes, elements, part, section and generally rigid material (*mat_rigid). These tools can either be fixed in space or moved using *boundary_prescribed_motion definitions in LS-DYNA. Dynfold interface will take user inputs in terms of direction and amount of motion and generate appropriate LS-DYNA cards.

Attachment of airbag to tools (clamping) is facilitated by user picking a set of nodes and defining which tool part to attach to. This attachment input from the user will be translated to *constrained_extra_nodes definitions in LS-DYNA.

Airbag self contact and contacts between airbag and the tools will be generated automatically by Dynfold using information provided in the process tab.

Spc_brith_death can also be used to model portions of the bag being restrained from moving. By default birth time is at time 0.0 and death time is infinity. But in some situations it may be necessasary to active the restraint at time other than beginning of the process.

BPMF(BOX) is another type of tool that facilitates housing of airbags in a final rectangular shaped box. Initial and final size of the box mesh is generated by Dynfold.

Contact definition between the box and airbag is automatically generated by Dynfold.

Airbags are often stitched as part of the final physical folding process. These stitches

often break during the deployment of airbag. Stiching tool allow the user to pick stitch locations on the airbag, stitching needle direction and stitch break force value. Using this information beam elements, tied contact betwwen the beams and airbag fabric and sensor definitions are generated by Dynfold.

1. Define Parameters

Define Project Step Name, Termination time, airbag tool Material Parameter

Fig.1 Process Setting

There is no default value for process termination time. User has to input, otherwise cant go to next page.

There are default values for all others parameters.

2. load airbag

Load airbag, Position airbag by translate; show airbag, or turn off show.

Fig.2 Airbag Loading

Load Airbag: load airbag from file.

Translate: Using LS-Prepost tools to position airbag. The airbag can be translated, Transform, Rotate, Scale, Project and so on.

Show On/Off: turn on and turn off to display airbag. All, None, Reverse: Highlight airbag parts.

3. Define Airbag Folding Tools There are four kind of tools: Load meshing, Spc_Birth_Death, BPMF(Box), Stitch.

3.1. load meshing

3.1.1. Load tool meshing file; Define tool attaching to bag:

Fig.3 Define tool of Load Mesh

Load: Load tool meshing and put tool parts in list. Highlight tool parts by select or unselect in the Tool Parts list.Translate: Using LS-Prepost tools to position tool. The tool can be translate, Transform, Rotate, Scale, Project and so on.Show On/Off: turn on and turn off to display tool.Contact Between tool and airbag: After load in tool meshing, define contact between tool and airbag parameters: Death time, Birth time and Thickness.Attach2Bag: Define attaching to bag nodes by Node set and part id. Pick and Add: Define Attaching to bag nodes by Pick node and Add nodes to Attach2Bag Node Set list. Replace: Replace Current selected Node Set item part id.

3.1.2. Define Load Meshing Tools Motion:

Fig.4 Define part Fixed motion with fix property

Fig.5 Define part Motion with motion property

Motion Type: Fixed; MotionModify: Modify selected tool motion in the list.

Preview: Preview defined tool motion and move tool to finial position on the screen.Home: Back to home position after preview.

3.1.3. Preview tool motion ( Home position and Final position):

Fig.6 Home position

Fig.7 Final position

3.1.4. Used Keyword:

*BOUNDARY_PRESCRIBED_MOTION_RIGID*CONTACT_AIRBAG_SINGLE_SURFACE

*CONTACT_AUTOMATIC_SURFACE_TO_SURFACE

*CONSTRAINED_EXTRA_NODE_SET*CONTROL_TERMINATION*DATABASE_BINARY_D3PLOT*DEFINE_CURVE*SET_NODE

3.2. Spc_Birth_Death

3.2.1. Pick nodes to define boundary spc node set.

Fig.8 Spc_BD Node Set define

Pick and Add: Define Boundary Spc nodes by Pick node and Add nodes to Spc Set Birth Death Node Set list. Replace: Replace Current selected Node Set parameter items, include translational and rotational constraint in local x,y,z-direction.

3.2.2. Used Keyword:

*BOUNDARY_SPC_SET_BIRTH_DEATH

*SET_NODE

3.3. BPMF(Box)

3.3.1. Define Original and Final position of the Box

Fig.9 Tool BPMF(Box) define

Contact Between tool and airbag: Define contact between box and airbag parameters: Death time, Birth time, Thickness, number of shells in x, y, z direction of the box, Gap between the box and airbag boundary, Emod(Young's modulus in MAT_NULL of box part material) and PR(Poisson's ratio in MAT_NULL of box part material).

Original/Target Position: To set the Original/Target position of the box.

Position: Get the min or the max point of the box's Original/Target position.

Show Original/Final Position: Show preview of Original/Target position of the box in graphics view.

Apply Pos: Apply Original/Target position of the box.

3.3.2. Preview Tool BPMF(BOX) Position

Fig.10 Tool box original position

Fig.11 Tool box target position

Fig.12 Tool box original and target position

For setting original/target position of the box, you can input x/y/z coordinates in the edit box, or pick a point in the view, also you can drag the arrow of the preview box axis.

3.3.3. Used Keyword

*NODE_NODE

*ELEMENT_SHELL

*PART_PART

*MAT_NULL

*SECTION_SHELL

*BOUNDARY_PRESCRIBED_FINAL_GEOMETRY

*CONTACT_AUTOMATIC_SURFACE_TO_SURFACE

*DEFINE_CURVE

3.4. Stitch

3.4.1. Define Stitch parts and parameters

Fig.13 Tool stitch define

Position: Get stitch start position.

Direction: Get stitch direction.

MinLen: Min lengthen of stitch beam elements.

Birth: Stitch birth time.

Death: Stitch death time.

TIMWIN: Trigger a status change when the value given by the sensor is less than or greater than the VALUE for a duration defined by TIMWIN.

Replace: Replace stitch parameters for defined items.

NID: Start node id of new created stitch part.

EID: Start element id of new created stitch part.

PID: Start part id of new created stitch part.

3.4.2. Example of stitch

Fig.14 Original stitch parts

Fig.15 New created stitch part( the green part )

3.4.3. Used Keyword

*NODE_NODE

*BEAM_ELEMENT

*PART_PART

*MAT_SPOTWELD

*SECTION_BEAM

*SENSOR_DEFINE_ELEMENT

*SENSOR_SWITCH

*SENSOR_SWITCH

*CONTACT_SPOTWELD

*SET_PART

*CONTROL_CONTACT3.5. Tuck1.1.1. Define tuck parts and parameters

There are three types of tuck tool: circle tuck, quad tuck and double quad tuck. 1. Circle tuck

Fig.16 Define Circle tuck

Common parameters for all types:

Pick deformable airbag part to be tucked: Check to pick target tuck parts from screen.

X/Y/Z_Trans: Translational constraint in local x/y/z-direction.

X/Y/Z_Rota: Rotational constraint about the local x/y/z-axis.

Birth: Input birth time.

Death: Input death time.

Wall Dist: Distance from circle center to the rigid wall.

Shell MT: Input the time which load shell start to move.

Parameters for circle tuck:

Center: Coordinate of the circle center.

Radius: Radius of the circle.

Tuck Dist: Input the final position of the tuck.

Wall Move Time: Input the time which wall start to move.

Fig.17 Preview of Circle Tuck

2. Quad tuck

Fig.18 Define Quad tuck

Parameters for quad tuck:

Center: Coordinate of the quad center.

Width: Input width of the quad.

Height: Input height of the quad.

Fig.19 Preview of Quad tuck

3. Double quad tuck

Fig.19 Define Double quad tuck

Parameters for double quad tuck:

Center: Coordinate of the double quad center .

Direction: Direction of double quad boundary .

Quad Dist1: Input the first distance of double quad.

Quad Dist2: Input the second distance of double quad.

Fig.20 Preview of Double quad tuck

1.1.1. Used Keyword

*RIGIDWALL_GEOMETRIC_FLAT.*DEFINE_CURVE*BOUNDARY_SPC_BIRTH_DEATH*SET_NODE*LOAD_SHELL*SET_SHELL*RIGIDWALL_PLANAR4. Project management

Management project: New, Output, Run DynaNew: Clear old job and Create New Job.Output: Output Keyword files.

Fig.21 DynFold Output

Run LS-DYNA: output keyword file and run LS-DYNA and put LS-DYNA result in same path as keyword file.

Fig.22 DynFold Run LS-Dyna

5. Tutorial:

In this tutorial, we have five steps, for all steps, we need to set process time and step name first, as Fig.1.

5.1. Step1. Use Load Mesh tool to roll airbag.

Airbag file: airbag.k.

Tool file: step1_tool.k.

5.1.1. Load Airbag

After process setting, goto the second page and Load airbag.k, if some parts' position is not good, you can use button "Translate" to adjust it. The UI as Fig.2 showing.

5.1.2. Load Tool file

Then goto the third page, and define a new tool "Load Mesh", load tool file step1_tool.k, all parts in this keyword file will be load mesh tool parts. The UI as Fig.3 showing.

5.1.3. Define tool attaching to airbag.

Since we want to roll the airbag when we rotate the roller tool parts, we should define a node set on the boundary of the airbag where near the roller tool part to attach the tool to airbag, see Fig.18, Fig.19 and Fig.20.

Fig.23 Define left roller attaching node set

Fig.24 Define right roller attaching node set

Fig.25 Define node set attaching roller to airbag

5.1.4. Define motion of Roller Parts

Define appropriate parameters for roller motion, include roller turns, roller diameter, roller thickness, roller rotate direction and roller translate direction. See Fig.21. Also, we can use "Privew" button to watch the final position of the roller part after motion, as Fig.6 and Fig.7.

Fig.26 Roller motion define

5.1.5. Output and Run LS-Dyna

Click button "Run Dyna", set output path, select check box "NextStep Name" and set name of next step, after finish of run LS-Dyna, it will load next step airbag automatically, then we can go on to do next step work.

Fig.27 Output and setting of run LS-Dyna

5.2. Step2. Use Load Mesh tool to compress the airbag.

Airbag file: airbag.k from step1.

Tool file: step2_tool.k.

Since the application create a new job and load airbag automatically from step1, we can goto the third page directly to load tool parts and define tool motion after set process time in the first page. We do not need to define node set to attach tool to airbag in this step.

Fig.28 Define tool motion to compress airbag

Fig.29 Home position of tool motion

Fig.30 Final position of tool motion

After tool motion define, output and run LS-Dyna, then goto next step.

5.3. Step3. Use Load Mesh tool to roll airbag as the same of step1, just in different direction.

Airbag file: airbag.k from step2.

Tool file: step3_tool.k.

5.3.1. Load Mesh tool file and define attach to bag node set

Fig.31 Define attach to bag node set

Fig.32 Define attach to bag node set

Fig.33 Define attach to bag node set

5.3.2. Define tool motion and preview

Fig.34 Home position of tool motion

Fig.35 Final position of tool motion

Fig.36 Define roller tool motion

After everything done, output and run LS-Dyna, and load next step airbag file automatically.

5.4. Step4. Define tool box to compress airbag.

Airbag file: airbag.k from step3.

After load airbag file automatically, add a new tool and select tool type as "BPMF(BOX)", you can see two transparent boxes in the view graphics with default parameters, the blue one is original position box, and the red one is the target position box, these two boxes are the same position at the beginning, in this example the gap between airbag and box is 10.0, and have 10 element in each direction of the box.

Select checkbox "Show Original Position" or "Show Final Position" to preview the box position of original or target, as Fig.10, Fig.11 and Fig.12. Then output and run LS-Dyna and goto next step automatically.

Fig.37 Define tool box

5.5. Step5. See the result of step4. The state of airbag after all steps above is Fig.33.

Fig.38 Final state of airbag