Solid State Phenomena Vol. 387

Abstract: To address the challenges met in the manufacturing of state-of-the-art multi-material structures, this work employs a novel one-shot stamping process with single-stamp forming of advanced high-strength steels (AHSS)-based multi-material structures consisting of dual-phase steel (DP780) and low-cost glass fibre-reinforced polyamide 6 (GF/PA6). The effects of DP780 surface treatment and forming temperature on interfacial bonding with GF/PA6 were first assessed using double cantilever beam (DCB) tests, alongside tensile tests of DP780 to assess post-stamping performance. Sandblasting on DP780 significantly improved bonding strength compared to non-treated surface, while the interfacial fracture energy (G_C) increased with forming temperature up to 350 °C before decreasing at higher temperatures, which is attributed to PA6 squeeze-out and DP780 surface oxidation. Although the tensile strength for DP780 decreased with increasing temperature, the yield strength peaked at 350 °C, identifying sandblasting and a forming temperature of 350 °C as the optimal processing conditions for DP780. Based on the optimal conditions determined, high-quality U-shaped demonstrator components were successfully produced with good surface finish, minimal polymer squeeze-out, and no observable defects, via further optimisation of the forming conditions.

Abstract: X-ray micro-computed tomography enables three-dimensional inspection of fiber-reinforced polymer composites. Quantitative mesostructural characterization remains challenging when voxel size does not permit reliable phase segmentation. This study presents a CT-based methodology for mesostructural characterization of unidirectional continuous-fiber polymer composites using line-profile descriptors. The approach extracts fixed one-dimensional intensity profiles within a defined internal volume of interest and computes a compact set of statistical and spatial descriptors. These include distributional moments, entropy, gradient-based measures, autocorrelation-derived correlation length, spectral band-energy ratios, and percentile-based run-length metrics. A technical quality control procedure verifies numerical consistency of the extracted feature tables. A one-at-a-time sensitivity analysis quantifies the influence of descriptor hyperparameters and identifies parameter groups that alter signal partitioning, particularly spectral cut-offs and run-length thresholds. Applied to pultruded composites, the descriptors resolve transverse heterogeneity across the section and systematic through-thickness trends in attenuation level, dispersion, spatial scale, and persistence of low-attenuation domains. The methodology provides a traceable low-dimensional representation of attenuation structure that can inform finite-element modeling through spatially parameterized material fields. Mechanical validation and descriptor–property calibration remain subjects for future work.

Abstract: This work focuses on the pultrusion of pre-consolidated tapes made of virgin polypropylene reinforced with glass fiber. A specially designed laboratory-scale pultrusion line was used, consisting of a heating/forming mold, a cooling mold, and the pulling system. A life cycle assessment was conducted to evaluate the environmental impact of producing a pultruded composite material with a constant cross-section of 100 mm² and a length of one meter. The cradle-to-gate approach was chosen to model the pultrusion process, which involves the three stages mentioned above. The analysis was performed using the CML 2016 method in the LCA for Experts (Sphera) software. The data used in this work to model the cradle-to-gate scenario are mainly derived from experimental measurements taken during the pultrusion process using sensors and from the literature. The specific Energy Consumption (SEC) was calculated for both operational conditions (1.41 MJ/m at v120 to 0.905 MJ/m at v180). Despite the defects found, the samples taken from the pultruded profile showed significant interlaminar shear strength (120 mm/min of 83.7 ± 9.6 MPa compared to 63.5 ± 17.3 MPa at 180 mm/min).

Abstract: Squeeze-flow testing is a commonly used experimental method for characterising the flow behaviour of high-performance C-SMCs under typical compression moulding conditions. A European benchmark exercise involving 14 research institutes is currently being conducted to identify the sources of variability in squeeze flow testing results and to support the development of a standardised testing methodology. Experimental testing of five C-SMC materials has been completed using a well-defined testing procedure.This paper focuses on the data processing stage of the benchmark exercise, in which experimental data collected from all participants are processed and analysed to extract information on raw material variability, force–gap height relationships, and flow-front profiles. Qualitative assessment of these results is used to identify the critical sources of variability, which subsequently informs a more detailed statistical analysis.

Abstract: Inherent limitations restrict the application of automated fibre placement (AFP) for manufacturing small components with complex geometries. As an alternative, flat, tailored preforms composed of fibre tows are first created and then formed into desired 3D geometries. However, the fibre orientation deviations between the as-manufactured and as-designed parts are inevitably introduced during forming. To address this issue, this study presents an iterative numerical forming/un-forming framework for the manufacture of highly aligned discontinuous preforms. At first, the as-designed preforms are “un-formed,” i.e., a reverse forming simulation, to achieve the corresponding flat preforms using the finite element modelling (FEM) method. To mitigate the deviations during forming, a pre-compensation strategy is then introduced by adjusting the initial fibre orientations derived from the un-forming analysis based on the calculated deviations through iterative re-forming simulations. A hypo-viscoelastic constitutive model implemented through a user-defined material subroutine captures the rate-dependent and orthotropic behaviour of the preforms during un-forming and re-forming. The FEM simulation results demonstrate significant reductions in fibre orientation deviation of formed 3D preforms through the iterative forming/un-forming framework, validating its applicability to a discontinuous fibre material on complex geometries.

Abstract: This study investigates the compaction behavior of woven flax rovings, a crucial aspect of the preforming stage in composite manufacturing. It focuses specifically on the challenges posed by their inherent heterogeneity and structural variability. Although the durability of flax-based composites is widely recognized, accurate numerical modeling of their processing, particularly for liquid composite molding (LCM), remains limited by the lack of detailed experimental data on roving mechanical behavior, including data capturing the inherent variability of the material. This research used a combined experimental approach, comprising computational microscopy for microscale deformation analysis and macroscopic compression tests, to characterize the mechanical response of flax rovings under compaction. Results highlight the need to develop sophisticated simulation frameworks that account for statistical variations in material properties but also the specificities of the flax roving response, which differs considerably from that of synthetic fibers rovings. The experimental dataset generated provides a valuable basis for identifying material parameters and validating advanced simulation frameworks aimed at improving performance predictions of manufactured components.