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Characterisation of Glass Fibre Polypropylene and GFPP based Fibre Metal Laminates at high strain rates
Fibre reinforced polymers (FRP) are finding increasing use in structures subjected to high rate loading such as blast or impact. Proper design of such structures requires thorough characterisation of the material behaviour over a range of loading rates from quasi-static to impact. This thesis inv...
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| Format: | Thesis |
| Language: | English |
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Blast Impact and Survivability Research Unit
2017
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| _version_ | 1867613955154771969 |
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| access_status_str | Open Access |
| author | Govender, Reuben Ashley |
| author2 | Langdon, Genevieive |
| author_browse | Govender, Reuben Ashley Langdon, Genevieive |
| author_facet | Langdon, Genevieive Govender, Reuben Ashley |
| author_sort | Govender, Reuben Ashley |
| collection | Thesis |
| description | Fibre reinforced polymers (FRP) are finding increasing use in structures subjected to
high rate loading such as blast or impact. Proper design of such structures requires
thorough characterisation of the material behaviour over a range of loading rates from
quasi-static to impact. This thesis investigated the quasi-static and impact response
of Glass Fibre Polypropylene (GFPP) in compression, bending and delamination. The
bending and delamination response of Fibre Metal Laminates (FMLs) based on GFPP
and aluminium was also investigated at quasi-static and impact rates.
High strain rate (5x10^2 to 10^3 /s) compression tests were conducted on GFPP using
a compressive Split Hopkinson Pressure Bar (SHPB) and a Direct Impact Hopkinson
Pressure Bar (DIHPB), in the through-thickness and in-plane directions. In both loading
directions, the peak stress of GFPP increased linearly with the logarithm of strain
rate. For in-plane loading, the failure modes were dominated by localised fibre buckling
and kink bands, leading to delamination. The through thickness loading produced
macroscopic shear and spreading failure modes. However, both of these failure modes
are linked to in-ply fibre failures, due to through thickness compression causing transverse
tensile strain. Previous studies of similar materials have not explicitly stated the
link between through thickness compression and fibre failure associated with transverse
tensile strain.
A novel test rig was developed for Three Point bend testing at impact rates. The
specimen was supported at the outer points on a rigid impacter and accelerated towards
a single output Hopkinson Pressure Bar (HPB), which impacted the specimen
at its midspan. Previous impact bend test rigs based on HPBs were limited to testing
specimens with deflections to failure up to approximately 1mm, whereas the rig implemented
herein measured deflections up to approximately 10 mm. This configuration
permits the output HPB to be chosen purely on the magnitude of the expected impact
force, which resulted in superior force resolution to configurations used in other
studies. The HPB Impact Bend rig was used to test GFPP and aluminium-GFPP FML
specimens, at impact velocities ranging from 5 to 12 m/s. The flexural strength of GFPP
increased with strain rate, while the flexural response of the FML specimens was relatively
insensitive to strain rate.
v
Several candidate delamination test geometries were investigated at quasi-static
displacement rates (1 mm/min), and the Single Leg Bend (SLB) test was identified as
suitable for adaptation to higher rate testing. Single Leg Bend delamination tests of
both GFPP and FML specimens were performed using the HPB Impact Bend rig, at
impact velocities of 6 to 8 m=s. The shape of the force displacement response for the
high rate testswas markedly different from the quasi-static tests, for both the GFPP and
FML specimens. Finite element (FE) simulation of the quasi-static and impact rate SLB
tests on GFPP indicated that the difference was probably due to the interaction of flexural
vibrations and stress waves in the specimen and the impacter cross member. The
experimental results and FE analysis suggest that the delamination fracture toughness
of GFPP decreases slightly as strain rate increases. High rate delamination tests on
FML specimens resulted in unstable crack growth. |
| format | Thesis |
| id | oai:open.uct.ac.za:11427/25150 |
| institution | University of Cape Town (South Africa) |
| language | eng |
| last_indexed | 2026-06-10T12:44:21.993Z |
| license_str | Not specified — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from UCTD — University of Cape Town Open Access Repository |
| publishDate | 2017 |
| publishDateRange | 2017 |
| publishDateSort | 2017 |
| publisher | Blast Impact and Survivability Research Unit |
| publisherStr | Blast Impact and Survivability Research Unit |
| record_format | dspace |
| source_str | UCTD — University of Cape Town Open Access Repository |
| spelling | oai:open.uct.ac.za:11427/25150 Characterisation of Glass Fibre Polypropylene and GFPP based Fibre Metal Laminates at high strain rates Govender, Reuben Ashley Langdon, Genevieive Nurick, Gerald composites delamination impact high strain rate Fibre reinforced polymers (FRP) are finding increasing use in structures subjected to high rate loading such as blast or impact. Proper design of such structures requires thorough characterisation of the material behaviour over a range of loading rates from quasi-static to impact. This thesis investigated the quasi-static and impact response of Glass Fibre Polypropylene (GFPP) in compression, bending and delamination. The bending and delamination response of Fibre Metal Laminates (FMLs) based on GFPP and aluminium was also investigated at quasi-static and impact rates. High strain rate (5x10^2 to 10^3 /s) compression tests were conducted on GFPP using a compressive Split Hopkinson Pressure Bar (SHPB) and a Direct Impact Hopkinson Pressure Bar (DIHPB), in the through-thickness and in-plane directions. In both loading directions, the peak stress of GFPP increased linearly with the logarithm of strain rate. For in-plane loading, the failure modes were dominated by localised fibre buckling and kink bands, leading to delamination. The through thickness loading produced macroscopic shear and spreading failure modes. However, both of these failure modes are linked to in-ply fibre failures, due to through thickness compression causing transverse tensile strain. Previous studies of similar materials have not explicitly stated the link between through thickness compression and fibre failure associated with transverse tensile strain. A novel test rig was developed for Three Point bend testing at impact rates. The specimen was supported at the outer points on a rigid impacter and accelerated towards a single output Hopkinson Pressure Bar (HPB), which impacted the specimen at its midspan. Previous impact bend test rigs based on HPBs were limited to testing specimens with deflections to failure up to approximately 1mm, whereas the rig implemented herein measured deflections up to approximately 10 mm. This configuration permits the output HPB to be chosen purely on the magnitude of the expected impact force, which resulted in superior force resolution to configurations used in other studies. The HPB Impact Bend rig was used to test GFPP and aluminium-GFPP FML specimens, at impact velocities ranging from 5 to 12 m/s. The flexural strength of GFPP increased with strain rate, while the flexural response of the FML specimens was relatively insensitive to strain rate. v Several candidate delamination test geometries were investigated at quasi-static displacement rates (1 mm/min), and the Single Leg Bend (SLB) test was identified as suitable for adaptation to higher rate testing. Single Leg Bend delamination tests of both GFPP and FML specimens were performed using the HPB Impact Bend rig, at impact velocities of 6 to 8 m=s. The shape of the force displacement response for the high rate testswas markedly different from the quasi-static tests, for both the GFPP and FML specimens. Finite element (FE) simulation of the quasi-static and impact rate SLB tests on GFPP indicated that the difference was probably due to the interaction of flexural vibrations and stress waves in the specimen and the impacter cross member. The experimental results and FE analysis suggest that the delamination fracture toughness of GFPP decreases slightly as strain rate increases. High rate delamination tests on FML specimens resulted in unstable crack growth. 2017-09-13T10:56:06Z 2011-12 2017-09-13T10:56:06Z 2011-12 Doctoral Thesis Doctoral PhD http://hdl.handle.net/11427/25150 eng application/pdf Blast Impact and Survivability Research Unit Faculty of Engineering and the Built Environment University of Cape Town |
| spellingShingle | composites delamination impact high strain rate Govender, Reuben Ashley Characterisation of Glass Fibre Polypropylene and GFPP based Fibre Metal Laminates at high strain rates |
| thesis_degree_str | Doctoral |
| title | Characterisation of Glass Fibre Polypropylene and GFPP based Fibre Metal Laminates at high strain rates |
| title_full | Characterisation of Glass Fibre Polypropylene and GFPP based Fibre Metal Laminates at high strain rates |
| title_fullStr | Characterisation of Glass Fibre Polypropylene and GFPP based Fibre Metal Laminates at high strain rates |
| title_full_unstemmed | Characterisation of Glass Fibre Polypropylene and GFPP based Fibre Metal Laminates at high strain rates |
| title_short | Characterisation of Glass Fibre Polypropylene and GFPP based Fibre Metal Laminates at high strain rates |
| title_sort | characterisation of glass fibre polypropylene and gfpp based fibre metal laminates at high strain rates |
| topic | composites delamination impact high strain rate |
| url | http://hdl.handle.net/11427/25150 |
| work_keys_str_mv | AT govenderreubenashley characterisationofglassfibrepolypropyleneandgfppbasedfibremetallaminatesathighstrainrates |