Composites are very versatile materials and offer advantages in many different ways, particularly if the application requires strength and stiffness, with low weight. For the Ballistic and Defence market, laminates provide effective ballistic protection at a much lower weight than metallic armour materials. Gurit has recently developed and qualified a ballistic phenolic prepreg, which is now being introduced to the market. Composite armour works by absorbing the kinetic energy of the projectile as it passes through the laminate.
There are three distinct stages involved in the stopping of a projectile: firstly, the blunting or deformation of the projectile, secondly, the slowing phase and, thirdly, the catching of the projectile. A composite laminate is made up of multiple layers of reinforcement fibers and resin. These layers are engineered to de-laminate at the impact of a projectile. This effect greatly enhances the slowing and stopping of the projectile over other materials.
The biggest advantage of composite armour over steel is the significantly lower weight. It can be up to 50% lighter, while providing equivalent protection against projectiles. Projectiles do not need to be bullets. In fact, artillery or mortar shells, aerial bombs, grenades and antipersonnel mines are all fragmentation devices whose steel casings burst into small fragments when their explosive cores go off.
The most common form of anti-ballistic composites is made from a combination of glass reinforcement and phenolic resin. The ballistic protection properties can be enhanced by altering the fibre and resin type: stronger fibres like s2 glass increase the ballistic protection of a laminate over e-Glass by 10-20%. Similarly, stronger epoxy resin can increase the anti-ballistic performance over phenolic resin. Yet, epoxy is less desirable due to its lower fire resistance.
As engineered materials, composites are designed to meet special requirements including threat levels, weight requirements and cost restrictions. Typically, solid composite armour is made from phenolic resin and reinforcement fibres showing a resin content in the region of 18-20%. Personal armour does not need to be structurally strong, so the composite plates used are made with even lower resin content laminates (<12% by weight). Ceramic composites offer a greater level of hardness, which can deflect or blunt the projectile before stopping it by under- lining composite or steel, again this application uses a different form of composite material.
Composite armour is used in the production of military vehicles, land-based shelters, ships and aircraft. It can be used as a structural material or as secondary plate armour just for protection. The need to reduce the weight of armoured vehicles has led to a large volume of composites being used in this area. Gurit’s new ballistic phenolic prepreg Pf 700 has been developed with this in mind. It meets the first requirements and conforms to the threat levels required for this market. It is also suitable for production of flat panels in a press moulding process or for moulding more complex parts by autoclaves.
PF 700 fact file :
PF 700 is a phenolic resin system, designed for defence and industrial applications with excellent FST behavior, high temperature resistance and ballistic performance.
PF 700 can be used to manufacture monolithic and sandwich structures with cure temperatures between 120 and 1600C (250 and 3200F).
PF 700 offers flexible processing methods by press or autoclave
Features :
• Available with heavy-weight woven S and R glass
• Long shelf and shop life
• Excellent FST behaviour
• Ideal for press moulding large flat components
• 10 – 30 minute cure times at 1600C
Gurit’s PF700 Ballistic Protection resin has been developed internally with input from industry leads specializing in defence applications. The PF700 pre-preg has also successfully been tested by Cranfield University, Impact and Armour Group. It conforms to the requirements of the US Military specification MIL-DTL-64154B.
PRODUCT INFORMATION
PF 700 phenolic resin system is available in a range of product formats to enhance the ballistic performance of the prepreg.
| PROPERTY | PF700-855g/m2 R-Glass | PF700-815g/m2 S-Glass | TEST STANDARD |
| Resin | Phenolic | Phenolic | – |
| Prepreg Weight | 1012 ± 50 g/m2 | 994 ± 50 g/m2 | EN 2329 |
| Volatile | < 2.7 % | < 6.0 % | – |
| Resin Flow | 7-15 % | 7-15 % | – |
| Tackiness | T0 / None | T0 / None | – |
| Fibre Material | R-Glass | S-Glass | – |
| Fabric Weight | 830 g/m2 ± 5 % | 815 g/m2 ± 5 % | EN 2331 |
| Weave Style | Plain Weave | Plain Weave | – |
| Resin Content | 18 ± 1 % | 18 ± 1 % | EN 2331 |
| Typical Roll Width | 1.27 m / 50 in | 1.27 m / 50 in | – |
PREPREG PROPERTIES
TRANSPORT & STORAGE
When stored sealed & out of direct sunlight.
| STORAGE TEMP. | UNIT | VALUE |
| -180C | months | 12 |
| +210C | weeks | 4 |
All prepreg materials should be stored in a freezer when not in use to maximise their useable life, since the low temperature reduces the reaction of resin and catalyst to virtually zero. However, even at -180C, the temperature of most freezers, some reaction will still occur. In most cases after some years, the material will become unworkable.
PREPREG PROCESSING
Recommended press moulding cure is 30 minutes at 1600C using a 2-50C/min ramp-rate and 1 – 6.4bar (0.1 – 0.4 MPa) of pressure. When press moulding low resin content prepreg pressures between 7 to 16 bar are required. Alternative times and temperatures are included in the table below. Panels should be pressed to stops to gain the cured thickness required.
| CURE TEMPERATURE | UNIT | VALUE |
| 1600C / 3200C | minutes | 30 |
AUTOCLAVE MOULDING
Recommended autoclave cure using a vacuum pressure of -1bar and autoclave pressure of 5bar, using 27 plies** of material (approximately 20mm thick cured laminate).
| CURE STEP | TIME | TEMP. | PRESSURE | VACUUM |
| 1 – Start | 0 mins | 300C | 0bar | -1bar |
| 2 – Pressurise | 40 mins | 400C | 5bar | -1bar |
| 3 – Ramp | 30 mins | 1400C | 5bar | -1bar |
| 4 – Dwell | 90 mins | 1400C | 5bar | -1bar |
| 5 – Ramp | 30 mins | 250C | 0bar | -1bar |
| 6 – Stop | 0 mins | 250C | 0bar | -1bar |
PREPREG PROPERTIES
RESIN PROPERTIES
All data presented in this datasheet is based on the testing of a single batch of material, tested at room temperature (210C + 710F)
| PROPERTY | UNIT | V |
| Density | g/cm3 | 1 |
| Viscosity at 250C | P | 1 |
| Solids at 1350C | % | 6 |
| Acidity at 250C | pH | 1 |
LAMINATE PROPERTIES
All data presented in this datasheet is based on the testing of a single batch of material, tested at room temperature (210C + 710F)
| PROPERTY | SYMBOL | PF700-855g/m2R-Glass | PF700-815g/m2S-Glass | TEST STANDARD | |||||
| Number of Plies | – | 4 | 4 | – | |||||
| Panel Manufacture Method | – | Autoclave | – | ||||||
| 00 Tensile Strength | XT | 532 MPa | 77 ksi | 823 MPa | 119 ksi | ISO 527-4 | |||
| 00 Tensile Modulus | ET11 | 27 GPa | 4 msi | 30 GPa | 4 msi | ISO 527-4 | |||
| 00 Compressive Strength | Xc | 159 MPa | 23 ksi | 195 MPa | 28 ksi | SACMA SRM1-94 | |||
| 00Compressive Modulus | Ec11 | 28 GPa | 4 msi | 33 GPa | 5 msi | SACMA SRM1-94 | |||
| 00 Flexural Strength | XF | 217 MPa | 32 ksi | 260 MPa | 38 ksi | ISO 14125 | |||
| 00 Flexural Modulus | EF11 | 14 GPa | 2 msi | 12 GPa | 2 msi | ISO 14125 | |||
| 00 Interlaminar Shear Strength | XILSS | 18 MPa | 3 ksi | 24 MPa | 4 ksi | ISO 1412 | |||
BALLISTIC PROPERTIES
| PRODUCT FORMAT | LAMINATE LAYERS | LAMINATE THICKNESS (mm) | LAMINATE WEIGHT (Kg/m2) | PROJECTILE / V50 STOPPING SPEED (M/S) |
| PF700, S2 Glass 815g/msq | 25 | 12.5 | 25-26 | 7.62mm, FSP / 772 m/s** |
| PF700, R Glass 830g/msq | 25 | 12.5 | 25-26 | 7.62mm, FSP / 709** |
