Surface Ply Damage

Surface Ply Damage 12

SURFACE PLY DAMAGE

1 INTRODUCTION

Surface ply damage methodology is presented in Section 2, based on Tsai-Hill Failure Index. However, any failure criterion maybe applied. All the applied 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 critical ply Failure Index. An example showing how to use this PATRAN Command Language (PCL) Function is presented in Section 3.

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

Surface ply damage analysis methodology is given next.

2 SURFACE PLY DAMAGE

Surface ply damage is simulated by the removal of one ply. This could be the first or last ply of the laminate depending on the configuration of the structure. In this analysis, all the plies of a given laminate are assessed for the impact of the loss of effectiveness of one ply. Surface ply damage analysis procedure is shown in Figure 2. A PCL function is used for this analysis, 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 stresses are given as follows:

applied stress in direction 1

applied stress in direction 2

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 material axes system (1,2) – see Figure 1 – are used to calculate the surface ply damage 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 1

S2_TENS = allowable tensile strength in direction 2

S2_COMP = allowable compressive strength in direction 2

S12 = allowable shear strength in plane 1,2

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

2.3 STRESS FACTOR

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

/ Eq. 1

Where, the ‘damaged’ laminate thickness corresponds to the removal of one ply. This could be the first or last ply of the laminate depending on the configuration of the structure. In this analysis, all the plies of the laminate are analysed for the impact of the loss of one ply. The next section deals with the Tsai-Hill Failure Index.

2.4 TSAI-HILL FAILURE INDEX

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

/ Eq. 2

Where,

allowable tensile or compressive strength in direction 1

allowable tensile or compressive strength in direction 2

allowable shear strength in plane 1,2

If is tensile,

If is compressive,

If is tensile,

If is compressive,

Or, re-written as:

/ Eq. 3

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

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.

3 EXAMPLE

A finite element model of a cantilevered section, built-in at its root, is shown 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 gives the 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 shown in Figure 1.

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

Figure 3. Finite element mesh.

Table 2. Laminate details.

Regions 1 to 3
PCOMP / Ply
Thickness / Area / 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

Figure 4. Deformed shape.

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

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 at element 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 at element 56 (PCOMP prop_prop3_region: root).

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

Figure 8. Files interaction.