7/29/2019 Poster Warnet DTAS 2007

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Compression after impact on curved composite panelsL. Warnet, R. Akkerman & P.E. Reed

University of TwenteFaculty of Engineering Technology,

P.O. Box 217, 7500AE, Enschede, NLl.warnet@utwente.nl

Experimental program

Both flat and curved panels were tested. Unidirectional

carbon T300 / PEI (Cetex) flat panels were first hot-

pressed. The curved panels required an extra rubber

pressing step. As shown in Figure 3, ultrasonic C-scan

was used to measure the projected delamination after

production, machining, impact and compression.

Introduction

The Compression After Impact (CAI) test method

involves an impact load on a flat composite plate,

followed by an in-plane compression test. Although

relevant for most aerospace applications, the use of a

flat plate limits the applicability of the method for complex

shapes. This work investigates the influence of curvature

of the specimen on the damage mechanisms occurring.

A typical example of a structure involving curvature and

relevant for the CAI load-case is shown in figure 1.

Curved plate specimens

A new CAI test method was developed for singularly

curved plates, using the existing the existing flat plate

equipment as a basis. Only the end fixtures of the

compression set-up were adapted. Figure 2 shows the

set-up for both impact and compression tests.

Several damage mechanisms can occur during the

impact test. The geometry of the curved plate was

chosen to make sure that delamination occurred before

snap through buckling or compression of the walls ofthe cylinder. This analysis based amongst others on

reference [1] resulted in a cylinder radius of 47.5mm

and a height of 17.5mm.

Figure 2: CAI for curved plates: Impact (left); Compression (right)

Figure 1: Example of a composite structure including curved sections:NH-90 composite trailing arm. Courtesy Stork SP Aerospace

Results

Impact testing of both types of geometry showed

qualitatively similar behaviour, typically an increase in

delamination surface with the impact energy,

accompanied with matrix cracking and minor fibre fractureonly at the highest energy level (20J).

Compression behaviour of the flat plates showed

extensive delamination from the impacted section. The

used instrumentation also showed a complex snap

buckling behaviour prior to failure. Despite their lower

thickness, the curved specimens failed in a compressive

way, showing a narrow damage zone over their full width,

through the impacted zone. This behavior is illustrated in

figure 4, with C-scans and roughly sketched damages for

the flat plate on the left, and for the curved panels on the

right side.

NH-90 helicopter

landing gear

Figure 3: Experimental and analysis procedure

Plate

Manufacturing

C-scan

Specimen

preparation

Impact

Testing

Geometry

Measurement

Image

Analysis

CAI

Testing

Image

Analysis

Plate

Manufacturing

C-scan

Specimen

preparation

Impact

Testing

Geometry

Measurement

Image

Analysis

CAI

Testing

Image

Analysis

Reference[1] G.A.O Davies, X.Zhang Impact prediction in composite structures,

Int. J. of Imp. Engng., pp. 149-170, 16 (1987).

Figure 4: Typical C-scan after impact and CAI for the flat plates (left)

and the curved panels (right)

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