This paper explores the performance of low-cost unidirectional carbon fibre towpregs with respect to line production speed and fibre volume fraction. Using an automated production line, towpregs were produced at different production speeds, resulting in modified fibre volume fractions. The towpregs were used to manufacture unidirectional composite plates, which were then tested to evaluate mechanical performance. The fibre straightness and interfacial void ratio of the composite plates were determined by statistical analysis of the samples’ optical micrographs. The results demonstrate that adjusting the line production speed enables targeted fibre volume fractions (FVF) to be reached, resulting in the composites having different mechanical performances (2039 MPa and 2186.7 MPa tensile strength, 1.26 and 1.21 GPa flexural strength for 59.8% and 64.4% FVF, respectively). It was shown that at lower production speeds and FVF, composites exhibit good consolidation and low porosity, which is highlighted by the better interlaminar shear strength performances (8.95% increase), indicating the limitations of manufacturing very high FVF composites. Furthermore, it was concluded that fibre straightness plays a key role in mechanical performance, as samples with a lesser degree of fibre straightness showed a divergence from theoretical tensile properties.

Contact resistances play a major role in Joule heating systems. Identifying contact resistances provides a better understanding of the heating process and increases the accuracy of the process models. In this study, contact resistances of the Joule heating section in a powder-epoxy-based towpregging line were explored. For different process parameters, such as production speed, tension, and temperature, contact resistances occurring between metal roller electrodes and dry carbon fibre tows (i.e. without powder-epoxy) were measured to gain an insight into the heating process. Moreover, the effect of contact resistance heating on the temperature profile of the carbon fibre tows was determined with an infrared thermal camera. A simplified finite element model was developed to calculate the temperature distribution onthe carbon fibre tow, which showed a good agreement with the experimental data. Results suggest that contact resistances in the towpregging line were significant and contact resistance heating changed the heating profile.

Eklemeli imalat teknolojileri, geleneksel imalat yöntemlerine kıyasla daha fazla esnekliğe izin veren doğaları nedeniyle giderek popülerleşmektedir. Bu teknolojilerin en yaygın kullanılan çeşidi olan eriyik yığma modelleme (EYM) işleminde çoğunlukla termoplastik polimer malzemeler katmanlar halinde serilerek üç boyutlu parçalar üretilir. Kristalizasyon davranışı sıcaklık değişimlerinden oldukça fazla etkilenen yarı kristal polimer malzemelerin EYM ile üretiminde, işlemdeki yüksek soğuma hızları mekanik özellikler üzerinde etkili olmaktadır. Bu çalışmada polipropilen türü yarı kristal malzemenin EYM işlemi esnasındaki kristalizasyon davranışı incelenmiştir. Bu bağlamda öncelikle katmanlı üretim metodunu simüle ederek sıcaklık profilini tahmin bir ısı transferi oluşturulmuş, bu model daha sonra kristalizasyon kinetiğini hesaplayan bir başka modelle iki taraflı olarak bağlanmıştır. Geliştirilen model farklı üretim parametrelerindeki kristalizasyon oranını eş zamanlı olarak tahmin edebilmektedir. Sonuçlar, malzeme kristalizasyon oranının ve buna bağlı olarak mekanik özelliklerin, EYM işlemi esnasındaki ısıtma ve soğutma işlemlerinin dikkatli şekilde ayarlanarak değiştirilebileceğini göstermektedir.

Purpose: This study aims to systematically investigate the cyclic shape memory behaviour of 4D-printed polylactic acid (PLA)-thermoplastic polyurethane (TPU) core-shell structures subjected to repeated programming-recovery cycles, with emphasis on understanding the influence of filament-level architecture and printing parameters. Design/methodology/approach: Core-shell PLA-TPU filaments were fabricated using a dual-extrusion fused deposition modelling process and reprinted into shape memory specimens. Cyclic thermomechanical tests were conducted under repeating programming-recovery cycles at 70 °C recovery temperature. A Box-Behnken response surface methodology was used to evaluate the effects of TPU content (30%–50%), layer thickness (0.1–0.3 mm) and print temperature (210–230°C). Shape recovery after the third cycle and a cyclic stability index (CSI) were selected as response variables. Findings: The results demonstrated that the core-shell 4D-printed specimens exhibit excellent shape fixity performance, with shape fixity ratios exceeding 98%–99%. Shape recovery also remained high after repeated programming-recovery cycles, ranged from 80.9% to 89.7% depending on processing conditions. The CSI, which serves as a measure of shape recovery retention over multiple programming cycles, was found to range between 84.9% and 92.2%. It was found that the PLA shell effectively preserved the programmed geometry, while the TPU core played a major role in elastic recovery. Increasing TPU content significantly improved both shape recovery and cyclic stability. Layer thickness exhibited a pronounced non-linear effect, with reduced performance at intermediate values (0.2 mm). Print temperature showed no statistically significant influence within the investigated range (210–230°C), indicating robustness of the core-shell architecture against moderate thermal variations during printing. Practical implications: The proposed approach enables scalable and cost-effective production of cyclically stable 4D-printed structures without material blending or specialised co-extrusion systems, supporting applications requiring repeatable thermally activated deformation. Originality/value: While core-shell architectures have been reported in the literature, existing studies have primarily focused on morphological and basic mechanical characterisation. Systematic investigations of functional behaviour, particularly cyclic thermomechanical shape memory performance of core-shell architectures, remain limited. This study addresses this gap by quantifying the influence of processing parameters on cyclic shape memory performance in 4D-printed PLA-TPU core-shell structures fabricated via a print-and-reprint approach.