Special requirements as to the strength and dimensioning of tanks can require a laminate of various materials such as thermoplastics and composites. A very high bond strength is required to ensure that tanks with this dual laminate construction have high operational security. Measurements to assess whether materials are suitable for this are the interlaminary shear strength and the tear resistance. Both tests are described in the DIN EN 13121-3.
Interlaminary shear strength according to DIN 13121-3
The requirements of the minimum interlaminary shear strength of thermoplastic linings in tanks made of fibre-glass reinforced plastics are described in section 7.6 of EN 13121-3. The European norm defines the minimum strengths which a laminate must stand up to in a tensile test.
For this, a conditioned test piece made of thermoplastic lining material bonded with FRP on both sides in defined positions is given a saw notch. After this, the tensile test takes place until the test piece breaks.
For PVDF as a lining material, a minimum shear strength of 5 N/mm² is stipulated. Polystone® PVDF SK and Polystone® PVDF GK have been successfully tested by an accredited testing institute according to this norm.
Tear resistance according to DIN EN 13121-3
To test the tear resistance of thermoplastic linings, minimum strengths for various laminate materials are defined in DIN EN 13121-3, section 7.8.
The test setup stipulates that test pieces are given boreholes under prescribed climatic conditions, into which fixed points are glued for a tensile test. At these fixed points, the test piece is pulled with a constantly increasing tensile strength until it breaks. The measured tensile strength and the fracture behaviour provide information on the quality of the laminate.
For PVDF as a lining material, a tear resistance of 3.5 N/mm² is stipulated. For the PP-H material, the minimum measurement is 2.5 N/mm² Polystone® PVDF GK, Polystone® PVDF SK and Polystone® P homopolymers have been tested by an accredited testing institute and meet the requirements for the strengths in this norm.