Method for analysing semi-finished products comprising a thermoplastic resin

A method for analyzing semifinished products comprising reinforcing fibers having an essentially unidirectional orientation and a thermoplastic resin, the method comprising:

• a first test comprising:
• preparing a stack of at least two identical semifinished products, the fibers of the adjacent semifinished products having a difference in orientation of 0°;
• heating the stack to a temperature above the melting temperature of the resin;
• cooling the stack to a temperature below the crystallization temperature;
• the stack being compressed in a direction of compression orthogonal to the orientation of the fibers of all the semifinished products during the heating and cooling;
• measuring the thickness of the stack in the direction of compression over time;
• determining the equivalent homogeneous viscosity of the stack from the measurement of the thickness of the stack over time;
• and
• a second test comprising:
• preparing a stack of at least two identical semifinished products, the fibers of the adjacent semifinished products having a difference in orientation of 90°;
• heating the stack to a temperature above the melting temperature of the resin;
• cooling the stack to a temperature below the crystallization temperature;
• the stack being compressed in a direction of compression orthogonal to the orientation of the fibers of all the semifinished products during the heating and cooling;
• measuring the thickness of the stack in the direction of compression over time;
• and
• determining the equivalent homogeneous viscosity of the stack from the measurement of the thickness of the stack over time;
• the method further comprising:
• determining a first parameter corresponding to the total thickness reduction of the stack of semifinished products during the first test;
• determining a second parameter corresponding to the ratio of the equivalent homogeneous viscosity of the stack of semifinished products from the second test to the equivalent homogeneous viscosity of the stack of semifinished products from the first test;
• and
• determining a third parameter corresponding to the ratio of the thickness H(t) of the stack of semifinished products from the first test after a reference time starting from the moment, during the heating step, of the onset of melting of the stack of semifinished products, to the thickness H0 at Tonset of the stack of semifinished products from the first test at the moment, during the heating step, of the onset of melting of the stack of semifinished products.