surface ply damage

8/8/2019 Surface Ply Damage

1/12

Surface Ply Damage 1

SURFACE PLY DAMAGE

1 INTRODUCTION

Surface ply damage is simulated by the removal of one ply. This could bethe first or last ply of the laminate depending on the configuration of thestructure. In this analysis, all the plies of a given laminate are assessed forthe impact of the loss of effectiveness of one ply.

Surface ply damage methodology is presented in Section 2, based on Tsai-Hill Failure Index. However, any failure criterion maybe applied. All theapplied and allowable stresses are given in the material (ply) axes system

(1,2) as presented in Figure 1. An element Failure Index in that of its criticalply Failure Index. An example showing how to use this PATRAN CommandLanguage (PCL) Function is presented in Section 3.


2/12


Figure 1. Material (ply), and laminate axes systems 1,2 and x,yrespectively. Ply applied and allowable stresses are given in the material(ply) axes system.

Surface ply damage analysis methodology is given next.

x

y

12

0/90

45

MATERIAL (PLY)AXES

SYSTEM (0)

MATERIAL (PLY)

AXES

SYSTEM (+45)

x

y

1

2 LAMINATEAXES

SYSTEM

LAMINATE

AXES

SYSTEM


3/12


2 SURFACE PLY DAMAGE

Surface ply damage is simulated by the removal of one ply. This could bethe first or last ply of the laminate depending on the configuration of thestructure. In this analysis, all the plies of a given laminate are assessed forthe impact of the loss of effectiveness of one ply. Surface ply damageanalysis procedure is shown in Figure 2. A PCL function is used for thisanalysis, activated by running a session file with the appropriate input data.The next section deals with the ply applied stresses.

2.1 APPLIED STRESS

Element ply-by-ply applied stresses in the material (ply) axes system (1,2) see Figure 1 are extracted from PATRAN database. The applied ply stressesare given as follows:

=1

applied stress in direction 1

=2

applied stress in direction 2

=12

applied shear stress in plane 1,2

The allowable stresses are addressed next.

2.2 ALLOWABLE STRESS

At a given operating temperature, ply allowable stresses in the materialaxes system (1,2) see Figure 1 are used to calculate the surface plydamage Tsai-Hill Failure Index. The allowable stresses are given as follows:

S1_TENS = allowable tensile strength in direction 1

S1_COMP = allowable compressive strength in direction 1S2_TENS = allowable tensile strength in direction 2S2_COMP = allowable compressive strength in direction 2S12 = allowable shear strength in plane 1,2

The next section addresses the stress factor due to surface ply damage.


4/12


2.3 STRESS FACTOR

Surface ply damage Stress Factor (SF) is given by Eq. 1 as:

LA IDAMAGED

LADESIGNEDASSFFACTORSTRESS =)( Eq. 1

Where, the damaged laminate thickness corresponds to the removal of oneply. This could be the first or last ply of the laminate depending on theconfiguration of the structure. In this analysis, all the plies of the laminateare analysed for the impact of the loss of one ply. The next section dealswith the Tsai-Hill Failure Index.

2.4 TSAI-HILL FAILURE INDEX

The ply Tsai-Hill Failure Index for surface ply damage analysis is given bythe following equation, which accounts for the surface ply damage stressfactor:

212

2

12

22

2

2

21

21

21

2

1 )()()()()(

S

SF

S

SF

S

SFSF

S

SFFI

+

+

=

Eq. 2

Where,

=1

S allowable tensile TENSS _1 or compressive COMPS _1 strength in direction 1

=2

S allowable tensile TENSS _2 or compressive COMPS _2 strength in direction 2

=12

S allowable shear strength in plane 1,2

If 1 is tensile, =1S TENSS _1

If 1 is compressive, =1S COMPS _1

If 2 is tensile, =2S TENSS _2

If 2 is compressive, =2S COMPS _2

Or, re-written as:

2

12

2

12

2

2

2

2

2

1

21

2

1 )()()()()(

S

SF

S

SF

S

SFSFSFFI

+

+

=

Eq. 3


5/12


The maximum Failure Index of an element corresponds to its maximum plyFailure Index. This Failure Index is displayed in PATRAN output for theelement.


6/12


Notes: 1) .ses file; 2) .pcl file; 3) .db file; 4)Results/Create/Results/Maximum (max of same ply numbers; then max of

all plies); 5) Results/Create/Fringe

Figure 2. Surface ply damage analysis procedure.

SURFACE PLY DAMAGE ANALYSIS: INPUT TO PCL FUNCTION 1)

PATRAN group name (PCOMP at a given temperature)

Load case name

Sub case nameResults coordinate system

Number of layers of laminate

Layer thickness

Allowable ply tensile stress in direction 1 S1_TENS

Allowable ply compressive stress in direction 1 S1_COMP

Allowable ply tensile stress in direction 2 S2_TENS

Allowable ply compressive stress in direction 2 S2_COMP

Allowable ply shear stress in plane 1,2 S12

CALCULATE STRESS FACTOR (SF) 2)

Damaged laminate: one ply removed

EXTRACT APPLIED STRESSES 2)

For each element, extract from PATRAN

database ply direct and shear stresses in the

material (ply) axes system 1,2

CALCULATE PLY TSAI-HILL FAILURE INDEX (FI) 2)

For each ply of each element to include the effect of surface ply damage Stress Factor

CREATE NEW RESULT CASE: PLY-BY-PLY FAILURE INDEX 2)

Create a new result case for each ply and add to PATRAN database

PLOT FAILUER INDEX 3)

Element-by-element plot 5)

DETERMINE ELEMENT FAILURE INDEX 3)

Each element is attributed its maximum ply Failure Index 4)


7/12


3 EXAMPLE

A finite element model of a cantilevered section, built-in at its root, isshown in Figure 3. It consists of three composite regions as given in Table 1.Unit pressure loading is applied on the surface of the elements. Table givesthe allowable stresses in the material (ply) axes system (1,2) see Figure 1.All the applied ply stresses are in material (ply) axes system (1,2) as shownin Figure 1.

Table 2 shows laminate details. Allowable stresses in the material (ply) axessystem (1,2) are given in Table 3. Figure 4 shows the deformed shape. TheTsai-Hill Failure Indices are presented in Figure 5 to Figure 7.

Figure 3. Finite element mesh.

BUILT-IN

EDGE

Prop1_region Prop2_region Prop3_region


8/12


Table 2. Laminate details.

Regions 1 to 3

PCOMPPly

ThicknessArea Lay-up No.

of

(mm) Plies

Prop_prop1_region 0.25 Tip 45/-45/-45/45 4

Prop_prop2_region 0.25 Mid-section 45/0/-45/-45/0/45 6

Prop_prop3_region 0.25 Root 45/0/90/-45/-45/90/0/45 8

Table 3. Allowable stresses in the material (ply) axes system (1,2).

Allowable Stresses

in the Material (Ply) Axes System (1,2)

Allowable Allowable Allowable Allowable Allowable

Tensile Compressive Tensile Compressive Shear

Stress in Stress in Stress in Stress in Stress in

Direction 1 Direction 1 Direction 2 Direction 2 Plane 1,2

S1_TENS S1_COMP S2_TENS S2_COMP S12

(MPa) (MPa) (MPa) (MPa) (MPa)

1500 1000 50 200 150


9/12


Figure 4. Deformed shape.

Figure 5. Surface ply damage analysis (one ply removed) maximum Tsai-HillFailure Indices (all plies 1 to 6). The maximum Failure Index is 0.90,occurring at element 56 (PCOMP prop_prop3_region: root).


10/12


Figure 6. Surface ply damage analysis (one ply removed) maximum Tsai-Hill

Failure Indices (ply 7: 0). The maximum Failure Index is 0.44, occurring atelement 56 (PCOMP prop_prop3_region: root).

Figure 7. Surface ply damage analysis (one ply removed) maximum Tsai-Hill

Failure Indices (ply 8: 45). The maximum Failure Index is 0.67, occurring atelement 56 (PCOMP prop_prop3_region: root).


11/12


3.1 FILES USED

The files used are given in Table 4. Files interaction is presented in Figure 8.

Table 4. Files used.

.bdf File surface_ply_damage.bdf

.ses File surface_ply_damage.ses

.pcl File surface_ply_damage.pcl


12/12


Figure 8. Files interaction.

.bdf FILE

Create a SET of elements of all PCOMPs

Run .bdf file, requesting STRESS output for the above SET

.ses FILE

Specify directory of .pcl file

Input data required by PCL functionRun session file to activate PCL function

(File/Session/Play)

.pcl FILE

Performs analysisCreates a new result case (Failure Index) for

each ply and adds to PATRAN database

.db FILE

Create a database by reading in the above .bdf file into an emptydatabase (File/Import/Model/MSC NASTRAN Input)

Read in .xdb file

Create property groups for all PCOMPs (Utilities/Group/Groups From

Properties)

surface ply damage

Documents