Fused filament fabrication (FFF) is one of the various types of additive manufacturing processes. Similar to other types, FFF enables free-form fabrication and optimised structures by using polymeric filaments as the raw material. This work aims to optimise the printing conditions of the FFF process based on reliable properties, such as printing parameters and physical properties of polymers. The selected polymer is poly(lactic) acid (PLA), which is a biodegradable thermoplastic polyester derived from corn starch and is one of the most common polymers in the FFF process. Firstly, the maximum inlet velocity of the filament in the liquefier was empirically determined according to process parameters, such as feed rate, nozzle diameter and dimensions of the deposited segment. Secondly, the rheological behaviour of the PLA, including the velocity field, shear rate and viscosity distribution in the nozzle, was determined via analytical study and numerical simulation. Our results indicated the variation in the shear rate according to the diameter of the nozzle and the inlet velocity. The shear rate attained its maximum value near the internal wall at high inlet velocities and smaller diameters. Finally, the distribution of the viscosity along the radius of the nozzle was obtained. At high inlet velocity, several defects appeared at the surface of the extrudates. At the highest shear rates, the extrudates underwent severe deformation. The defects predicted via numerical simulation were reasonably consistent with that observed from an optical microscope. Hence, these results are effective for selecting the printing parameters (i.e. nozzle diameter, feed rate and layer height) to improve the quality of the manufactured parts.

International audienceAcoustic emission (AE) and infrared thermography (IT) are simultaneously combined to identify damage evolution in carbon fibre reinforced composites. Samples are subjected to tensile static loads while acoustic emission sensors and an infrared camera record the acoustic signals and the temperature variations respectively. Unsupervised pattern recognition procedure is applied to identify damage mechanisms from acoustic signals. Thermodynamic arguments are introduced to estimate global heat source fields from thermal measurements and anisotropic heat conduction behavior is taken into account by means of homogenization technique. A spatial and time analysis of acoustic events and heat sources is developed and some correlation range in the AE and IT events amplitude are identified

To adapt liquid reactive processes to thermoplastic composite manufacturing, synthesis kinetics of PA6 from ε-caprolactam monomer have been investigated. This reaction involves simultaneously polymerization of monomers and crystallization of growing chains. It has been studied by DSC over a wide range of isothermal and non-isothermal conditions, and TGA, DSC and WAXS experiments were performed on polymerized samples. Shape of DSC curves allowed to identify the degree of interaction between polymerization and crystallization. At high temperature or high heating rate, polymerization occurs first and crystallization is delayed because of the low supercooling. When phenomena are fully decoupled, the final properties are close to conventional PA6. For lower conditions, crystallization depends on the availability of chains and polymerization controls the synthesis time. The high mobility of the environment favors the final degree of conversion and the properties of the crystalline phase. At very low temperature, a two-step crystallization is observed, due to a critical molecular weight that is required for nucleation and the degree of conversion could be affected by entrapment of reactive species in crystals.