High strain rate tests on fibre metal laminates

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High Strain Rate Tests on

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High Strain Rate Tests on

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High Strain Rate Tests on

Fibre Metal Laminates

A. Vlot

Published and distributed by: Delft University Press Mekelweg 4 2628 CD Delft The Netherlands Telephone + 31 (0) 15 278 32 54 Fax +31 (0)15278 1661 e-mail: DUP@DUP.TUDelft.NL by order of:

Faculty of Aerospace Engineering Delft University of Technology Kluyverweg 1 P.O. Box 5058 2600 GB Delft The Netherlands Telephone +31 (0)152781455 Fax +31 (0)152781822 e-mail: Secretariaat@LR.TUDelft.NL website: http://www.lr.tudelft.nl

Cover: Aerospace Design Studio, 66.5 x 45.5 cm, by:

Fer Hakkaart, Dullenbakkersteeg 3, 2312 HP Leiden, The Netherlands Tel. + 31 (0)71 51267 25

90-407-1592-0

Copyright © 1998 by Faculty of Aerospace Engineering

All rights reserved.

No part of the material protected by this copyright notice may be reproduced or utilized in any form or by any means, electron ic or

mechanical, including photocopying, recording or by any information storage and retrieval system, without written permission from the publisher: Delft University Press.

Contents

1. Introduction 3 2. Tensile tests 6 3. Residual strength 9 4. Condusions 13 5. References 14

1.

IntroductÎon

Fibre Metal Laminates are a new family of laminates built up from 0.2 to 0.3 mm thin aluminium alloy sheets bonded into one laminate by intermediate 0.1 to 0.2 mm thin fibre/epoxy layers. The laminates are developed at Delft University of Technology, primarily for aircraft structures. The variant with aramid fibres is called ARALL, while a new generation of laminates called GLARE incorporates S2-g1ass fibres. Fibre Metal Laminates have a high fatigue resistance due to intact fibres in the wake of the crack which restrain crack opening, see Figure 1. The material combines the formability and machinability of aluminium alloys and the high specific strength of composite materials. After curing the adhesive at 120 °C, the cured laminate has an internal stress system at room temperature because of the difference of the coefficients of thermal expansion of the constituents. Unfavourable tensile stresses are present in the aluminium layers which are balanced by compression in the fibre/ epoxy layers. This internal stress system in the aluminium layers can be reversed by a plastic poststretching operation. Different lay-ups are commercially available (see Table 1). ARALL-3 is currently in production for the

C-17 aft cargo door and GLARE-3 is selected for the Boeing 777 impact resistant bulk cargo floor.

The laminates can be applied in various thicknesses; e.g. a 3/2 lay-up means a laminate with three aluminium layers and two intermediate fibre/ epoxy layers:

[Al/p rep regl Al/prepregl Al].

The fibre/ epoxy layers of a 3/2 lay-up can be multiple cross-plied 0/90 layers or ca~ be unidirectional (UD), e.g.:

[2024/0°/90°/2024/90%°/2024]

is a cross-plied 3/2 lay-up, with aluminium 2024-T3 layers.

GLARE material has an excellent impact resistance compared to carbon reinforced composites and even performs better than monolithic aluminium at high impact velocities (100 mis) [1, 2, 3]. The first application of GLARE in the Boeing 777 cargo floor is driven by the impact properties while other impact sensitive parts of aircraft are being considered, e.g., parts of the cockpit, cargo bay liners, and leading edges of wings and tailplanes.

A part of the good impact resistance is attributed to the strain rate dep ende nt behaviour of the glass fibres. Several authors found an effect of the strain rate on the longitudinal tensile strength of glassl epoxy. Some results are compiled in Figure 2. A strain rate in the order of 100 5.1 will be reached during impacts of foreign objects with a velocity of 10 mis (e.g., dropped tools), whereas velocities in the order of 100 mis may cause strain rates in the order of 1000 5.1 (e.g., runway debris). The strength relative to the quasi-static value, at a strain rate in the order of

10'\

stated by the authors is plotted in Figure 2 as function of the strain rate. Chiao and Moore [4] tested S-glass/ epoxy strands in a tensile test machine with a maximum crosshead speed of 0.83 mm/s and found an

increase of the longitudinal tensile strength of 23% for an increase in strain rate from 1.97 10-4 S·l (quasi-static) to 1.97 S'l. No influence for carbon/epoxy was observed. However, Daniel and Liber [5] found no or only a slight negative influence on the strength of S-glass/ epoxy and carbon/epoxy in the longitudinal direction, and an increase for aramid/epoxy. They used a tensile test machine with a maximum crosshead velocity of 5.1 mis and reached strain rates up to 18 S'l. Harding and Welsh [6] performed very high strain rate tests on carbon and glass fibre composites up to strain rates of 870 S·l with a Hopkinson's pressure bar technique. They reported no influence of the strain rate for carbon in fibre direction, but a relatively large strain rate dependency for glass/epoxy. They found a dramatic increase of the tensile strength from 348 MPa at 10-4 S·l to 899 MPa at 870 S·l in fibre direction (increase of 116%). The modulus increased from 19.6 to 48.6 GPa. The fracture appearance changed. In quasi-static tests, the damage was limited to the fracture surface, while at the higher strain rat es the entire gauge section was damaged by matrix cracking and debonding. Woven fibre reinforced laminates show a larger strain rate dependence than unidirectional materials probably due to a dynamic effect in the stretching of the 'kinks' in the fabrics. The strength in fibre direction is mainly affected by the fibre properties, although also the adhesion between the fibres and therefore the matrix will have an influence. Large effects of the strain rate were found for the more 'matrix dominated' off-axis and shear properties of composites [7,8].

grade AI alloy fibre orientation poststretch

GLARE-1 7475-T76 glass unidirectional yes

GLARE-2 2024-T3 no

GLARE-3 2024-T3 0°/90° cross-ply no GLARE-4 2024-T3 0°/90%° cross-ply no ARALL-1 7475-T6 aramid unidirectional 0.4%

ARALL-2 2024-T3 no

ARALL-3 7475-T76 0.4%

T able 1. Different grades of Fibre Metal Laminates.

Metallic materials like aluminium alloys show a strain rate dependent behaviour because of thermal activation in the material. The strain rate will create an effective temperature rise. No strong strain rate dependency was reported for high-strength aluminium alloys which are used in Fibre Metal Laminates [9]. Aluminium alloys are still in the athermal region at a strain rate of 5 105

S'l. Kawata, et al. [10] reported a small decrease (1 to 4 %) of the strength of 2024-T4 and 7075-T651 at strain rates of 7.4 102

S'l. However, Davies and Magee [11] showed a slight increase (3%) in the strength for 7075-T6 in the whole

The go:)d impact performance of GLARE makes the laminate astrong candidate for impact damage prone sections, i.e., areas were birds, ice, stones or cargo may hit the structure. Also ot her aspects related to the strain rate dependent behaviour may be relevant, e.g., the damage tolerance of the aircraft fuselage in the presence of damage caused by an explosion in the fuselage or by non-contained engine debris. In both cases the fuselage wiII be penetrated and the internal pressure may cause a tensile load in the fuselage skin which

is

large enough to create a fast running crack that must be stopped to prevent a catastrophe. Whether the crack will be arrested depends on the time it takes for the intern al pressure to vent, fracture toughness of the skin, and strength and stiffness of the stiffening and crack stopping elements of the fuselage. In general, the crack will run in the longitudinal direction of the fuselage, and the stiffening elements will be frames. In many aircraft, crack stoppers are applied to increase the damage tolerance. Usually the fuselage is designed to be able to carry a two-bay crack with the centre frame broken caused by an engine fragment under the normal operating cabin pressure of the aircraft. In this case, the static strength and toughness of the materials are considered. However, because of the dynamics of the process, especially in the case of an internal explosion, the dynamic strength of the crack stopper material and dynamic toughness of the fuselage skin will be relevant. Arrest of unstable cracking can be influenced by dynamic effects.

ResuIts of high strain rate tensile tests on GLARE and monolithic aluminium are discussed here in order to shed more light on the dynamic behaviour of GLARE. T ensile tests were performed on unnotched and notched specimens of potential crack stopper and fuselage skin materials (chapter 2). The dynamic toughness of the materials was determined with special residual strength specimens with two collinear cracks which link-up under loading causing a dynamic failure of the specimen (chapter 3).

2. T

ensile tests

2.1 Test method

The tested materials are divided in two typical high strength crack stopper materials (GLARE-1 and 7075-T6) and two typical fatigue resistant fuselage skin materials (GLARE-3 and 2024-T3).

A. Crack stopper materials

- GLARE-1, in a 3/2 lay-up: three 0.3 mm thin layers of 7475-T76 bonded together by two layers of unidirectional S2-glassl epoxy prepreg. The material is poststretched. The total thickness of GLARE-1 is 1.44 mm, in the following lay-up:

[7475/0°/0°/7475/0°/0°/7475]

- Aluminium 7075-T6 (bare), thickness of 1.62 mmo

The specimen width was limited by the capacity of the 10 kN of the test machine. The unnotched specimens, type A as is shown in Figure 3, were applied for the crack stopper materials. Strain gages were applied to measure the strain during the test.

B. Fuselage skin materials

- GLARE-3, in a 2/1 lay-up: two 0.2 mm thin 2024-T3 layers bonded by two cross-plied S2-glassl epoxy layers. The material is in the as cured condition. The total thickness is 0.69 mm, with the following lay-up:

-Aluminium 2024-T3 (bare), thickness 0.64 mm, chemically etched from a thickness of 1 mmo

The specimen width was again limited by capacity of the 10 kN of the test machine. Notched and unnotched specimen types B1, B2, and B3 were tested, see Figure 3. Specimen type B2 contains two relatively blunt notches (K, = 1.86 for isotropie mate rial) and type B3 relatively sharp notches made by a saw cut.

All materials were tested at three loading rates: 2 mm/min (quasi-statie), 1

mis

and 20 mis. The quasi-statie tests were performed with a 10 kN MTS servo-hydraulic test machine, while the higher loading rates were achieved with a 10 kN Schenk hydro-pulse test machine. The cross-head speeds were constant during the tensile test. Three tests were done for each material and loading rate to obtain reliable results.

2.2 Results

Table 2. Typical stress-strain curves of both materials on the three loading rates are shown in Figure 4. The ultimate stress and strain to failure as a function of the strain rate is plotted in Figure 5. As can be seen in this figure, 7075-T6 shows a small decrease of the strength, while the strength of GLARE-1 increases by 16% at a strain rate of 110 S·l. The energy stored in the tensile specimen is calculated from the area under the force-displacement plot and is given in Figure 6 relative to the area of the cross section of the specimens. As indicated in this figure, the energy at the quasi-statie loading is higher for aluminium alloys because of their higher ductility, but at the higher loading rates GLARE and the monolithic counterpart are ab Ie to store the same amount of energy. The strength of the fibre/ epoxy layer is estimated, assuming a stress of 520 MPa in the 7475-T76 layers at the moment of failure (independent of the strain rate). The results are given in Table 2. The increase of the strength of the S2-glass fibre/ epoxy layers is relatively small in comparison to the majority of the literature data in Figure 2.

A lot of delarnination is visible in the GLARE specimens after the tests. There was no difference in the fracture appearance of the statie and high strain rate specimens.

material strain rate Young's strain to failure ultimate estimated

(S·l) modulus (GPa) (%) stress strength of

(MPa) fibre/ epoxy layer (MP a) GLARE-1 2.62 10-4 62 4.49 1125 2133 8.5 54 6.27 1184 2291 110 39 5.25 1309 2624 7075-T6 2.6 10-4 68 9.67 573 9.5 56 9.19 532 120 40 8.45 540

T ab Ie 2. Average test results for unnotched crack stopper materials.

The average test results for the unnotched and notched skin materials are given in T able 3. The ultimate stress es which are given in this table for the notched specimens are related to the net-section, i.e., the cross section at the noteh. These ultimate stresses are shown in Figure 7 as function of the strain rate. The same trends as for the crack stopper materials are visible in this plot. GLARE-3 shows an increase in strength of 11, 21, and 24%, for no notch, a blunt notch and a sharp notch respectively; while 2024-T3 shows a decrease of 11 and 16% for the blunt and sharp notch respectively. Apparently the strain rate effect is stronger for the sharper notches due to fact that the strain rate at the root of the notch is raised by the stress concentration.

The unnotched GLARE specimens show a different fracture behaviour at high strain rates. The specimens fractures at two locations with more delamination and buckling due release of elastic energy of the specimen than under statie loading (see Figure 8).

.e.

material cross- no blunt sharp

head notch notch notch

speed

(mis) displace- ultimate displace- ultimate displace- ultimate

ment at stress ment at stress ment at stress

failure (MPa) failure (MPa) failure (MP a)

(mm) (mm) (mm) GLARE-3 3.3 10.5 _{7.81 682 3.68 504 2.88 446} 1

-

- 4.97 541 4.54 485 20 7.43 754 4.88 608 3.69 553 2024-T3 3.3 10.5 21.5 451 3.33 430 1.49 382 1 - - 2.84 395 2.13 379 20

-

-

3.04 383 3.32 320

3.

Residual strength

3.1 Introduction

The dynamic fracture of GLARE and 7075-T6 has been investigated on long sheet specimens with two adjacent cracks (Figure 9). This specimen was also used by VaSek and Schijve [12] to investigate the dynamic behaviour of Al 7075-T6. When a load is applied to the specimen, the two cracks in the specimen will link-up and a single crack is formed. A sudden rise of the stress intensity at the ends of this single crack will be caused by this linking. This increase of the stress intensity can initiate a dynamic fracture of the specimen. When the ligament between the cracks is toa long, bath cracks behave almast independently. In that case, a crack will initiate from bath sides of each crack instead of a link-up prior to final failure.

The same principle was used to study the dynamic behaviour of GLARE crack stoppers. A test specimen as indicated in Figure 10 was applied. The skin of this specimen was critical. When the cracks in the skin material link-up, the crack stopper feels adynamic laad and fails.

3.2 Specimens and materials

The same dimensions as used by Vasek and Schijve were taken for the dynamic toughness measurements: 160 mm wide and 1000 mm long. The specimen was long in order to store enough elastic energy for the rapid failure. The two collinear cracks were made by sawing slots with a fine jeweller's saw. Aluminium 7075-T6 (bare) with a thickness of 1.59 mm and GLARE-l with a thickness of 1.43 mm, consisting of 0.3 mm 7475-T76 and 0.1 mm S2-glass/epoxy layers were tested. The GLARE material was poststretched and has the following lay-up:

[7475/0°10°17475/0°10°17475].

Specimens with six different crack lengths were tested for bath materiais. The total length of the two cracks plus the width of the ligament between the two cracks was kept constant (60 mm, see Figure 9). This means for the longest crack length of a=30

mm, the length of the ligament was 0 (one single crack length 2a=60 rnm). The ligament length was increased up to 12 mm (a=24 mrn).

The specimen depicted in Figure 10 was used to study the dynamic behaviour of crack stoppers. The crack stopper was riveted with protruding he ad rivets (diameter 4 mm) to the skin. The skin material was 2024-T3 (clad) with a thickness of 1.6 mmo Four specimens were tested: two specimen with a completely cut skin (a = 80 mm) and two with a cut of 35 mm at bath edges of the specimen (see Table 4 and Figure 10).

The GLARE-l crack stoppers had two 0.3 mm 7475-T76 layers and one S2-glass/epoxy layer, and a total thickness of 0.85 mm:

GLARE-1 is poststretched material. The 7075-T6 crack stoppers had a thickness of 1.0 mmo The saw cuts were made with a fine jeweller's saw.

crack stopper crack length ultimate maximum crack opening in skin load (kN) strain in at maximum

(mm) crack stram m

stopper crack stopper

(%) (mm) GLARE-1 80 10.54 0.53 2.3 (completely cut) 35 56.5 1.2 1.0 7075-T6 80 9.08 0.64 1.4 (completely cut) 35 57.7 0.51 0.47

Table 4. Crack stopper specimens.

3.3 Test set-up and procedure

The Crack Opening Displacement (COD) is measured with an optical device. A narrow light beam faUs perpendicular to the crack (saw cut) and is partly received by a photo-ceU at the other side of the crack. The measured light intensity by the photo-cell is proportional to the crack opening. The equipment was calibrated and a linear relationship between the output voltage and the COD was checked. The width of the light beam was 1 mm and was positioned at 5 mm from the crack tip of the specimens with the collinear cracks (see Figure 11). For the crack stopper specimens the cent re line of the beam was positioned at a distance of 10 mm from the edge of the specimen (see Figure 11).

For the crack stopper specimens a strain gage was mounted on the crack stopper at the cent re line of the specimen between two rivets.

The load on the specimen and the COD of the coUinear cracked specimens were recorded with a sample frequency of 15 kHz and stored on a disk. The load, COD, and strain of the crack stopper specimens were sampled with 10 kHz.

The specimens were mounted in a 1000 kN MTS testing machine and fastly loaded with a square-step load from 0 to 200 kN, except the coUinear crack specimens with one single crack (a = 30 mm) and the crack stopper specimens with a crack over the full

width. These specimens were loaded quasi-statically up to failure.

3.4 Results

The COD was measured for the collinear crack specimens at a position of 5 mm from the crack tip. which is 25 mm from the centre of the specimen. A (virtual) COD at the

centre of the specimen was calculated from this measured COD2s, assuming an elliptical

crack opening:

COD COD_x afuil 1.8091 COD₂₅

l7..af~l-x2)

where x=25 mm and ajull = 30 mmo

The statie gross stress vs. COD curves for the collinear crack specimens with a single

crack are shown in Figure 12. Typical dynamic curves are shown in Figure 13 for

7075-T6 and GLARE-l for a = 26 mmo The complete set of graphs is given in the Appendix.

The link-up of the two cracks can be seen in the COD-plot as a small rise prior to final

failure of the specimen. Table 5 gives the results for the link-up stress and ultimate gross

stress with corresponding COD values. The link-up point can not be accurately

determined for the 7075-T6 specimen at a = 28 mmo For the crack lengths smaller than

26 rnm no link-up is found prior to final failure. For these crack lengths the interaction

between the two cracks is too small.

material a Ulink.up CODlink.up Uult CODult

(mm) (MPa) (mm) (MP a) (mm) 7075-T6 30 - - 204.2 0.45 28 ? ? 193.5 0.52 27 168.6 0.15 197.7 0.53 26 216.0 0.26 221.9 0.49 25

-

- 218.4 0.64 24 - - 235.7 0.56 GLARE-l 30

-

-

329.5 2.34 28 315.8 0.78 346.6 1.36 27 328.2 0.80 360.2 1.62 26 350.0 0.75 361.9 1.59 25 -

-

393.1 1.27 24 -

-

402.5 0.86 22

-

- 426.4 0.94

The gross stress as function of the crack length a is plotted in Figure 14. The ultimate gross stress for 7075-T6 shows a slight decrease for a decreasing crack length from a=30 mm, before a rise to the link-up boundary, as was also found by VaSek and Schijve. GLARE-1 exhibits a small increase of the strength, starting from a=30 mmo The gross ultimate stress for 7075-T6 drops from 204.2 to 193.5 MPa (a reduction of 5.2%), whereas the gross stress of GLARE 1 rises from 329.5 to 361.9 MPa (an increase of 9.8%). No difference was found between the fracture surfaces at static and dynamic loading.

The ultimate load, maximum strain, and opening at maximum strain are given in Table 4 for the crack stopper specimens. The static force vs. opening plots for the completely cracked skin are shown in Figure 15. Although the riveted GLARE-l crack stopper is 20% thinner, it can carry 16% more load than the 7075-T6 crack stopper. The aluminium crack stopper reaches a maximum strain of 0.6%, which is slightly higher than the 0.5% of the GLARE crack stopper. The dynamic test results are given in Figure 16. As can be seen in this figure, the skin becomes critical at approximately the same load for the aluminium and GLARE crack stopper (57.7 and 56.5 kN respectively). However, the strain in the GLARE crack stopper rises after the failure of the skin to a value of 1.0 to 1.2 %, whereas the aluminium crack stopper immediately fails at apprroximately the same value as in the static tests (0.51%).

4. Conclusions

1. Tensile tests on unnotched specimens revealed a small decrease of the ultimate stress of the aluminium alloy 7075-T6 (6%) and an increase for GLARE-1 Fibre Metal Laminates (16%) at loading rates of 100 S-I.

2. Tensile test on notched specimens showed that the strain rate sensitivity increases for sharper notches. An increase of the ultimate stress of 11, 21 and 24% was determined for GLARE-3 Fibre Metal Laminates without a notch, with a blunt notch and with a sharp notch respectively. Al 2024-T3 shows a decrease of 11 and 16% for blunt and sharp notches respectively.

3. Residual strength tests carried out under dynamic conditions revealed a slightly smaller ultimate gross stress for the aluminium 7075-T6 alloy (5%) and a 10% higher residual strength for the GLARE-l Fibre Metal Laminate.

4. Initia! tests on crack stopper specimens show that the GLARE crack stopper fails at a higher strain for a higher loading rate, while no effect of the strain rate was found for the 7075-T6 crack stopper. This means that a GLARE crack stopper will be able to carry a higher load than static strength for a small period of time.

Acknowledgement

The research described in this paper has been carried out under contract with the Dutch Department of Civil Aviation (RLD).

5. References

1. A. Vlot, Impact Properties of Fibre Metal Laminates, Composites Engineering, Vo1.3, No.10, pp.911-927, 1993.

2. A. Vlot, Low-velocity Impact Loading on Fibre Reinforced Aluminium Laminates

(ARALL) and Other Aircraft Sheet MateriaIs, dissertation Delft University of Technology,

1991.

3. A. Vlot, Impact loading on fibre metal laminates, Int.]. Impact Engng., Vol. 18(3), pp.291-308, 1996

4. T.T. Chiao and R.L. Moore, Strain Rate Effect on the Ultimate Tensile Stress of

Fiber Epoxy Strands, in: e.J. Hilado (ed.), Carbon Reinforced Epoxy Systems, Technomie USA, pp.1-4, 1974.

5. I.M. Daniel and T. Liber, Strain Rate Effects on Mechanical Properties of Fiber Composites, NASA CR-135087, 1976.

6.

J.

Harding and J. Welsh, A Tensile Testing Technique for Fibre-reinforced Composites at Impact Rates of Strain, J Materials Science, Vo1.18, pp.1810-1826, 1983. 7.

J.

Harding, K. Saka and M.E.e. Taylor, The Effect of Strain Rate on the Tensile Failure of Woven-reinforced Carbon/glass Hybrid Composites, in: C.Y. Chiem et al. (eds.) , Impact Loading and Dynamic Behaviour of Materiais, pp.515-522, DGM Verlag, 1988.

8. C.Y. Chiem and Z.G. Liu" The Relationship Between Tensile Strength and Shear Strength in Composite Materials Subjected to High Strain Rates, ]. Eng. Materials and

Technology, Vol.11O, pp.191-194, 1988.

9. e.G. Burstow, M.e. Lovell and A.L. Rodgers, Mechanisms of Dislocation MotÏon in 7075-T73 Aluminium Alloy at Strain Rates Round 105 s·l, in: Mechanical Properties of

Materials at High Rates of Strain, Proc. of the Fourth International Conference on the

Mechanical Properties at High Rates of Strain, pp.317-322, Oxford, 1989.

10. K. Kawata, S. Hashimoto, S. Sekino, N. Takeda, Macro- and Micro-mechanics of High-velocity Brittleness and High-velocity Ductility of Solids, in: K. Kawata and

J.

Shioriri (eds.), Macro- and Micro-Mechanics of High Velocity Deformation and Fracture, Proc. IUTAM Symposium, Tokyo, Japan, Springer-Verlag, 1985.

11. R.G. Davies and e.L. Magee, The Effect of Strain-rate Upon the Tensile Deformation of Materials, ]. Engng. Materials and Technology, pp.151-155, 1975.

12. A. Vasek and J. Schijve, Residual Strength of 7075·T6 Al·alloy Under High Load Rates, report Delft University of Technology, 1994.

controlled delamination

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Figure 1. Fatigue crack in Fibre Metal Larninate

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collinear crack specimen lmm - . ; :.0.-'1 ! I ________ crack ----'-'-~ , i I, l·gh I

r---

I t beam

:j

_,

.

-5mm I mm , '

--

!

:

l-

'

crack _ _ _ _ ,..;' i~/'...;' ; i crack stopper crack stopper specimen

I1

;

!

i ; -; - : light bea : I i ; , , , I IOmm I !

Figure 11. Position of the light beam of the optical device tO measure the crack opening.

350

....

_.

300 250 Gross stress 200 (MPa) ₁₅₀ 100 50 0 0 0.5 1.5 2 2.5 3 COD (mm)

Figure 12. Measured static gross stress as function of crack opening displacement.

COO( gross stress (MPa)

450 10 GLARE-1 400 ₉ 350 ₈ \ .• r 300 ~. 7 6 250

-stress

---

5 200 / / -₄ 150 - _/ / _. r ₃ 100 --

-

_{- 2} 50 - r • COD

.

~ . , 0 . ./ I I 0 0 20 40 60 80 100 120 time (ms) COO(mm) gross stress 450 ₁₀ (MPa) 7075-T6 400 9 350 8 7 300 6 250 5 200 4 150 stress .-1"/ I 3 100 _{, /}

.-\ ₂ ,.,-50 ..

-

COD /

,

',

0 : \ , ' \ ₀ 0 10 20 30 40 50 60 time (ms)

gross stress (MPa) 425 375 325 275 225

-

--GLARE 1 7075-T6 175 +,----~----~--_.----~--~~---~ 22 23 24 25 26 27 28 29 30 crack length a (mm)

force (kN) straln (%)

l

' - - - rl 0.6 14 GLARE-1

t

I

strain 12 I 0.5 10

I

t

0.4

:

1

r

03

T

0.2 4 !

+

0.1 2

o

~---~---~---+_----~~---~ 0

o

2 3 4 5 opening (mm) 10 , . - - - , - 0.7 7075-T6 9 0.6 8 7 0.5 6 0.4 force (kN)5 strain (%) 0.3 4 3 _0.2 2 0.1 O~---+---r_--~~--====~=====+O

o

1 2 3 4 5 opening (mm)

force (kN) opening-(0.1 mm) 60 GLARE-1 ₁₄ 50 strain 12 _{(0.1 %)} ". 40 10 30 8 6 20 4 10 2 0 0 0 10 20 30 40 time (ms) 50 60 force (kN) opening (mm) 60 6 strain 50 5 (0.1 %) 40 4 30 3 20 2 10 0 0 0 10 20 30 40 50 60 70 80 time (ms)

w

o

Al 7075-T6,

a

=

28

rnrn

gross stress (Mpa)

450~---~

400

350

300

250

200

150

100

50

o

~

t

_.

I

-===-=+=

\

I

\

-~

/

\

---,"~

-Al 7075-T6,

a

=

27

rnrn

gross stress (MPa)

COD

(mm)

450

rl---~"

-

9

400

-

.

-

₈

350

-

-

7

300

6

250

5

200

_

.

-

-

4

3

stress

150

'

/ /

100

-

2

50

-

.

-

_COD

₁

o

L:---=;:;;

•

h , , " - . - - ( \ I

0

o

10

20

30

40

50

60

w tv

Al 7075-T6,

a

=

26

rnrn

gross stress

(Mpa)

o

7075-T6 ,' - -~I" -."

10

20

L,;OD /. J \

--.-30

40

50

- -- - - -- - -- - - _{"---_.---}

---Al 7075-T6,

a

=

25

rnrn

CCD (mm)

450

grass stress (UPa)

I

10

400 .

350

-.-300

250

200

150 -.

-100

50

.. ~-~~/ stress

_

..

. /

'"

_ . ,/ '

_

.. - / / ' . /

o

10<'-"/

O

r ·

+Hf.

10

20

30

_

.. ~" ..

-."

COD

J'

40

-.- 9

r

I

•

8

7

....,

"'"

Al

7075-T6,

a

=

24

rnrn

o

10

20

::mess

30

40

COD (mm)

50

. _ - - -

_.---GLARE-l,

a

=

28

rnrn

COD (mm)

gross stress (MPa)

450

10

400

9

350

8

7

300

stress

~~

6

250

5

200

4

150

3

100

₂

50

₁

0

0

0

20

40

60

80

100

120

!.H 0\

GLARE-l, a

=

27

rnrn

gro •••

tr •••

(MP.)

CCD

(mm)

450

I

I

10

400

350

300

250

200

150

9

8

7

6

5

4

3

s:i/:

F

•

•

·1 \

t:

100

COD

o

20

40

60

80

100

120

time (ms)

--

- -

-GLARE-l,

a

=

26 rnrn

COD(mm)

gross stress (MPa)

450-I

GLARE-1

400

..

.

10

-0-

9

350

-

,

\ or.

"

300

.

-

...

.

-0-

8

-0-

7

250

I

~

stress

200

_.

. / / / .0-

6

-0-

5

-0-

4

150

.-

/ / ., / . -0-

3

100

_

.

, ~ -0 -

2

'./ _COD

50

-

1

-

r.' / , ~ , / O -~ I ,

l

1

"

0

0

20

40

60

80

100

120

w

00

GLARE-l,

a

=

25

rnrn

gross stress 450

_

COD (mm)

(MPa)

~

r

10

400

.

.

-350

..

..

-300

-

.

-250

-

.

-200

-

.

-150

_

.

-100

-

..

50

-

.

-. /.~.

O~

o

,.. / ) -' .. { I

20

40

---~

....

/ .. stress ./ ;'

COD

...,-60

80

/~."., ". .,.~ Ij ....-I

100

-

:

-

9

-

8

.

.

-

7

-

.

-

6

-

.

-

5

-

.

-

4

,-

3

.

_I

_.

'

I

·

2

:

;

-

-

1

I .

o

120

-GLARE

-

l,

a

=

24 rnrn

gross stress (MPa)

450

-.-400

-

.

-350

-

.

-300

_

.

-250

200

150

-

.

-100

_

.

-50

-o

/

stress _/ r //

_/

/ /

/1

/

/

20

40

r.'

·

/

~/

60

. / /" ... ,

COD

(mm)

10

__ /~ -t-

9

,...#~., -~-_ /

_/

'

~

8

/ - / ",.,." ,/ ",./ j

/

_

i

l

-

7

/ / ! -- 1

80

COD

6

5

~

-

4

i ; -:~, -

3

;

.

, 2

-~

1

1

-

-

-

1

"-

0

100

120

time (ms)

t5

GLARE-l,

a

=

22

mm

gross stress

(MPa)

450

--400

-

.

-350

-.

-300

-

.-250

-200

~-150

~-100

-

.

-/ -/

/./

/

/

-<,,' ./ " , .

./~-~-, /

~

COD

--

---

-<

50

r/

~

J

!

'

I, . J

I

i\

-\

---~---1--- ~-~

o

20

40

60

80

100

120

140

COD (mm)

10

9

-~

8

7

6

5

4

3

-

2

1

o

Series 01: Aerodynamics

01. F. Motallebi, 'Prediction of Mean Flow Data for Adiabatic 2-D Compressible Turbulent Boundary Layers'

1997/ VI + 90 pages / ISBN 90-407-1564-5

02. P.E. Skare, 'Flow Measurements for an Afterbody in a Vertical Wind

Tunnel'

1997 / XIV + 98 pages / ISBN 90-407-1565-3

03. B.W. van Oudheusden, 'Investigation of Large-Amplitude 1-DOF Rotational Galloping'

1998 / IV + 100 pages / ISBN 90-407-1566-1

04. E.M. Houtman / W.J. Bannink / B.H. Timmerman, 'Experimental and

Computational Study of a Blunt Cylinder-Flare Model in High Supersonic Flow'

1998 / VIII

+

40 pages / ISBN 90-407-1567-X

05. G.J.D. Zondervan, 'A Review of Propeller Modelling Techniques Based on Euler Methods'

1998 / IV + 84 pages / ISBN 90-407-1568-8

06. M.J. Tummers / D.M. Passchier, 'Spectral Analysis of Individual Realization LDA Data'

1998 / VIII

+

36 pages / ISBN 90-407-1569-6 07. P.J.J. Moeleker, 'Unear Temporal Stability Analysis'

1998/ VI + 74 pages / ISBN 90-407-1570-X

08. B.W. van Oud heusden, 'Galloping Behaviour of an Aeroelastic Oscillator with Two Degrees of Freedom'

1998/ IV + 128 pages / ISBN 90-407-1571-8

09. R. Mayer, 'Orientation on Ouantitative IR-thermografy in Wall-shear Stress Measurements'

1998 / XII

+

108 pages / ISBN 90-407-1572-6

10. K.J.A. Westin / R.A.W.M. Henkes, 'Prediction of Bypass Transition with Differential Reynolds Stress Modeis'

1998/ VI + 78 pages / ISBN 90-407-1573-4

11. J.L.M. Nijholt, 'Design of a Michelson Interferometer for Ouantitative Refraction Index Profile Measurements'

1998/ 60 pages / ISBN 90-407-1574-2

12. R.A.W.M. Henkes / J.L. van Ingen, 'Overview of Stability and Transition in External Aerodynamics'

1998/ IV

+

48 pages / ISBN 90-407-1575-0

13. R.A.W.M. Henkes, 'Overview of Turbulence Models for External

Aerodyna-mies'

Series 02: Flight Mechanics

01. E. Obert, 'A Method for the Determination of the Effect of Propeller Slip-stream on a Static Longitudinal Stability and Control of Multi-engined Aircraft'

1997 / IV

+

276 pages / ISBN 90-407-1577-7

02. C. Bill I F. van Dalen I A. Rothwell, 'Aircraft Design and Analysis System (ADAS)'

1997 I X + 222 pages I ISBN 90-407-1578-5

03. E. Torenbeek, 'Optimum Cruise Performance of Subsonic Transport

Air-craft'

1998 / X

+

66 pages / ISBN 90-407-1579-3

Series 03: Control and Simulation

01. J.C. Gibson, 'The Definition, Understanding and Design of Aircraft Handling Oualities'

1997 I X + 162 pages I ISBN 90-407-1580-7

02. E.A. Lomonova, 'A System Look at Electromechanical Actuation for Primary Flight Control'

1997 / XIV

+

110 pages / ISBN 90-407-1581-5

03. C.A.A.M. van der linden, 'DASMAT-Delft University Aircraft Simulation

Model and Analysis TooI. A Matlab/Simulink Environment for Flight Dyna-mics and Control Analysis'

1998 I XII + 220 pages I ISBN 90-407-1582-3

Series 05: Aerospace Structures and

Computional Mechanics

01. A.J. van Eekelen, 'Review and Selection of Methods for Structural Reliabili-ty Analysis'

1997 I XIV + 50 pages I ISBN 90-407-1583-1

02. M.E. Heerschap, 'User's Manual for the Computer Program Cufus. Ouick

Design Procedure for a CUt-out in a FUSelage version 1 .0' 1997 / VIII

+

144 pages / ISBN 90-407-1584-X

03. C. Wohlever, 'A Preliminary Evaluation of the B2000 Nonlinear Shell

Element 08N.SM'

1998 I IV + 44 pages / ISBN,90-407-1585-8

04. L. Gunawan, 'Imperfections Measurements of a Perfect Shell with Specially Designed Equipment (UNIVIMP)

Series 07: Aerospace Materials

01. A. Valiek / J. Schijve, 'Residual Strenght of Cracked 7075 T6 AI-a"oy

Sheets under High Loading Rates'

1997 I VI

+

70 pages I ISBN 90-407-1587-4

02. I. Kunes, 'FEM Modelling of Elastoplastic Stress and Strain Field in

Centre-cracked Plate'

1997 / IV + 32 pages / ISBN 90-407-1588-2

03. K. Verolme, 'The Initial Buckling Behavior of Flat and Curved Fiber Metal

Laminate Panels'

1998 / V"I + 60 pages / ISBN 90-407-1589-0

04. P.W.C. Prov6 Kluit, 'A New Method of Impregnating PEl Sheets for the

/n-Situ Foaming of Sandwiches'

1998/ IV

+

28 pages / ISBN 90-407-1590-4

05. A. Vlot I T. Soerjanto / I. Yeri / J.A. Schelling, 'Residual Thermal Stress es

around Bonded Fibre Metal Laminate Repair Patches on an Aircraft Fusela-ge'

1998/ IV + 24 pages / ISBN 90-407-1591-2

06. A. Vlot, 'High Strain Rate Tests on Fibre Metal Laminates'

1998/ IV + 44 pages / ISBN 90-407-1592-0

07. S. Fawaz, 'Application of the Virtual Crack Closure Technique to Calculate

Stress Intensity Factors for Through Cracks with an Oblique E"iptical Crack Front'

1998 / V"I

+

56 pages / ISBN 90-407-1593-9

08. J. Schijve, 'Fatigue Specimens for Sheet and Plate Material'

1998 / VI + 18 pages / ISBN 90-407-1594-7

Series 08: Astrodynamics and Satellite Systems

01. E. Mooij, 'The Motion of a Vehicle in a Planetary Atmosphere'

1997 / XVI + 156 pages / ISBN 90-407-1595-5

02. G.A. Bartels, 'GPS-Antenna Phase Center Measurements Performed in an

Anechoic Chamber'

1997 / X + 70 pages / ISBN 90-407-1596-3

03. E. Mooij, 'Unear Quadratic Regulator Design for an Unpowered, Winged

Re-entry Vehicle'

Dynamic tensile tests are performed on unnotched and notched Fibre Metal Laminates (GLARE) and monolithic aluminium 7075-T6 up to a strain rate of 100 s-1. Aluminium shows a small decrease of the strength (6%), while the strength of (GLARE) increases 16%. An indication of the dynamic toughness of the materials was obtained using a residual strength specimen with two collinear cracks which link-up during loading causing rapid fracture of the specimen. Aluminium 7075-T6 showed a slight decrease of the ultimate gross strength (5%) while GLARE failed dynamically at a higher gross stress (10%). Initial dynamic tests carried out on crack stopper specimens reveal an increase of the failure strain of a GLARE crack stopper.