Fig. 1
Schematic comparison of fiber metal laminates: standard and inverse hybrid laminate (InverTec) [3]. FRP, fiber-reinforced polymer
Table 1
Configuration of the analyzed series of FMLs
| Series | Configuration of FRP laminate layers | Laminate code (variant 0°) | Laminate code (variant 90°) |
|---|---|---|---|
| S1 | 3x CFR-TP PA6GF60 | [0G/90G/0G/Alu]s | [90G/0G/90G/Alu]s |
| S2 | 3x CFR-TP PA6GF60 | ||
| S3 | 1x CFR-TP PA6CF60/4x-CFR-TP PA6GF60 | ||
| S4 | 1x CFR-TP PA6CF60/4x-CFR-TP PA6GF60 | [0C/90G/0G/90G/0G/Alu]s | [90C/0G/90G/0G/90G/Alu]s |
[i] CFR-TP, carbon fiber-reinforced thermoplastic; GF, glass fiber; FML, fiber metal laminate; FRP, fiber-reinforced polymer; PA, polyamide
Fig. 2
Example of fiber arrangement in S1 series laminates: variant 0° (S1.0) (A) and variant 90 (S1.90) (B). GF, glass fiber; PA, polyamide
Fig. 3
Diagram of the process of forming an inverted hybrid laminate (InverTec)
Table 2
Parameters of variothermal consolidation of InverTec inverted laminate sheets
| Steps | Pressure (bar) | Temperature (°C) | Time (min) |
|---|---|---|---|
| Heating and plasticizing of polymer matrix | 20 | 260 | 6.5 |
| Consolidation of the FRP composite | 30 | 260 | 3.5 |
| Cooling phase and solidification of the polymer melt | 30 | 60 | 16.5 |
[i] FRP, fiber-reinforced polymer
Fig. 4
View of the ILSS test using a three-point-bending load (short beam test) [3]. ILSS, inter-laminar shear strength
Table 3
Parameters for the ILSS SBS test
| System | Zwick\Roel 5.0 |
|---|---|
| Temperature | 23°C |
| Humidity | 46% |
| Test speed (constant) | 2 mm/min |
| Span length | 8 mm |
| Bending die | 5 mm |
| Support rollers | 2 mm |
[i] ILSS, interlaminar shear strength; SBS, short-beam shear
Table 4
Mean values of shear stresses τmax and τB determined by the ILSS SBS test for laminates listed in Table 3 [3]
| τmax [MPa] | τB [MPa] | |||
|---|---|---|---|---|
| Configuration | ||||
| Series | 0 | 90 | 0 | 90 |
| S1 | 33.3 | 48.5 | 26.6 | 40.0 |
| S2 | 49.6 | 20.7 | 44.2 | 16.0 |
| S3 | 57.3 | 20.3 | 46.8 | 17.4 |
| S4 | 52.6 | 41.7 | 42.7 | 35.6 |
[i] ILSS, interlaminar shear strength; SBS, short-beam shear; τmax, maximum shear stress; τB, shear stress at the moment of first failure
Fig. 5
Cross-sectional views and 3D images obtained with CT of series S1–S4 specimens in Variants 0 and 90. Colored areas on 3D images indicate damages caused by delaminations and cracks in the matrix. Defects marked on the images: springback damage (i), core and FRP delaminations (ii), matrix cracks in FRP layers in planes parallel to the bending axis (iii), and matrix cracks in planes perpendicular to the bending axis (iv). CT, computed tomography; FRP, fiber-reinforced polymer
Fig. 6
Views of the defects observed at the interface between the FRP and the Al6061 layers of series S1.0 specimens: detachment of FRP layers (i), slight delamination on the core surface (ii), and fiber bulking (iii). The areas marked within the squares are shown at different magnifications (B and C). The cross section seen is in the plane perpendicular to the bending line of series S1 specimen 0 (S1.0), as observed by SEM/BSD. FRP, fiber-reinforced polymer; SEM/BSD, backscattered electron detector-based scanning electron microscopy
Fig. 7
Views of defects observed in series S1.90 specimens: matrix cracks (i) and (ii); GF cracks (iii). The indicated areas are shown at different magnifications (B and C). The cross section is in the plane perpendicular to the bending line of series S1.90 specimen, as seen by SEM/BSD. GF, glass fiber; SEM/BSD, backscattered electron detector-based scanning electron microscopy
Fig. 8
Views of defects in series S2.0 specimens: delamination (i), matrix cracks (ii) and (iii), and GF cracks (iv). The indicated areas are shown at different magnifications (B, C, E). Cross section is in the plane perpendicular to the bending axis of the specimens, observed by SEM/BSD. GF, glass fiber; SEM/BSD, backscattered electron detector-based scanning electron microscopy
Fig. 9
Views of the damage to the series S2.90 specimens: matrix cracks (i), FRP and laminate core delamination (ii), matrix and GF delamination (iii), and GF cracks (iv). The indicated areas are shown at different magnifications (B–F). Cross section is in the plane perpendicular to the bending axis of the specimens, observed by SEM/BSD. FRP, fiber-reinforced polymer; GF, glass fiber; SEM/BSD, backscattered electron detector-based scanning electron microscopy
Fig. 10
Views of the damage to the series S3.0 specimens: cracks on the laminate surface (i), bulking of GFs (ii), delamination of GFRP layers from the core (iii), and cracking of GFs (iv). The indicated areas are shown at different magnifications (B–E). Cross section is in the plane perpendicular to the bending axis of the specimens, viewed using SEM/BSD. GF, glass fiber; GFRP, glass fiber–reinforced polymer; SEM/BSD, backscattered electron detector-based scanning electron microscopy
Fig. 11
Views of damage to the series S3.90 specimens: PA matrix cracks (i); delamination of GFRP layers from the core (ii); delamination of GFs and PA matrix (iii) and (iv); and PA matrix cracks in the CFRP layers (v). The indicated areas are shown at different magnifications (B–E). Cross section is in the plane perpendicular to the bending axis of the specimens, as observed by SEM/BSD. CFRP, carbon fiber-reinforced polymer; GF, glass fiber; GFRP, glass fiber-reinforced polymer; PA, polyamide; SEM/BSD, backscattered electron detector-based scanning electron microscopy
Fig. 12
Views of damage to series S4.0 specimens: cracks in GFRP layers (i), delamination of GFRP layers from the core (ii), PA matrix cracks and fiber delamination in CFRP layers (iii), PA matrix cracks and CF bulking (iv), and GF cracks (v). The indicated areas are shown at different magnifications (B–D). Cross section is in the plane perpendicular to the bending axis of the specimens, viewed using SEM/BSD. CF, carbon fiber; CFRP, carbon fiber-reinforced polymer; GFRP, glass fiber–reinforced polymer; PA, polyamide; SEM/BSD, backscattered electron detector-based scanning electron microscopy
Fig. 13
Views of damage to the series S4.90 specimen: surface cracks in CFRP layers (i), cracks in GFRP layers (ii), delamination of GFRP layers and core (iii), PA matrix cracks and fiber delamination in CFRP layers (iv), CF bulking (v), and delamination of PA matrix and fibers in GFRP layers (vi). The indicated areas are shown at different magnifications (B–E). Cross section is in the plane perpendicular to the bending axis of the specimens, viewed using SEM/BSD2. CF, carbon fiber; CFRP, carbon fiber–reinforced polymer; GFRP, glass fiber–reinforced polymer; PA, polyamide; SEM/BSD, backscattered electron detector-based scanning electron microscopy
Table 5
Summary/classification of damage in laminate plies in relation to ply fiber orientation and stress distribution
| Type of load | Tension | Compression | ||
|---|---|---|---|---|
| FRP layer fiber arrangement | 0 | 90 | 0 | 90 |
| Type of damage | Presence in specimens S.1/S.2/S.3/S.4 | ||||
|---|---|---|---|---|---|
| GFRP–core delaminations | +/+/+/+ | −/+/± | ±/−/− | −/−/−/+ | |
| Cracks on the external surface of the laminate | −/+/± | +/+/+/+ | −/−/−/− | −/−/+/+ | |
| Matrix cracks | CFRP | −/−/−/+ | +/+/+/+ | −/−/−/+ | −/−/−/+ |
| GFRP | n.e./n.e./+/+ | n.e./n.e./−/+ | n.e./n.e./+/+ | n.e./n.e./+/+ | |
| Fiber cracks | GFRP | −/+/± | −/−/−/− | −/−/−/− | −/−/−/− |
| CFRP | n.e./n.e./−/− | n.e./n.e./−/− | n.e./n.e./−/− | n.e./n.e./−/− | |
| Fiber bulking | GFRP | n.a.* | ±/± | ±/± | |
| CFRP | n.a.* | n.e./n.e./−/+ | n.e./n.e./−/+ | ||
[i] Legend: “−” indicates not observed; “+” indicates observed;
[ii] “n.e.”: CFRP layer was not existing in the analyzed configuration of specimen.
[iii] n.a.*: bulking can be connected to the compressed plies only.
[iv] CFRP, carbon fiber-reinforced polymer; FRP, fiber-reinforced polymer; GFRP, glass fiber–reinforced polymer