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The 3D printing parameters are known to have a significant impact on manufactured parts, and the layered morphology of these parts makes mechanical design analysis for engineering applications difficult. In this work, the tensile strengths and microhardness of 3D printed polylactic acid (PLA) specimens with different orientations and numbers of individual layers of mesh material (polyvinyl chloride – PVC) were investigated as a laminate composite. Composite specimens were obtained using 3D printing via fused deposition modelling (FDM). Moreover, the influence of printing parameters (i.e. infill density and layer height) and the number and orientation of reinforced meshes on the mechanical response was investigated. Fracture strength of PLA/PVC laminate composites ranges from 31.30 MPa (3 PVC mesh layers; mesh height position: 25 %│50 %│75 %; infill density: 60 %; PVC mesh orientation: 90°│45°│90°; layer height: 0.2 mm) to 18.62 MPa (without PVC mesh; infill density: 30 %; layer height: 0.1 mm) demonstrating a significant impact of the number of the PVC mesh layers, infill density of PLA and layer height on the final mechanical parameters of printing PLA/PVC elements. The surface hardness at the micro load level showed that the number of reinforcement layers affects the microhardness value, as well as material filling and mesh orientation. The specimen with the following parameters gave the best results: layer height: 0.2 mm; 3 PVC mesh layers; infill density: 60 %; PVC mesh orientation: 90°│45°│90°. The average hardness values for one layer and three layers of mesh were in accordance with tensile test results.

Composite materials and structures are widely used and applied in many industries owing to their advantages, such as satisfactory stiffness-to-mass ratio and corrosion resistance. However, during their operating life, responsible parts subject to complex loads may change and their properties might deteriorate. To ensure structural integrity it is necessary to monitor and regularly check the performance of composite structures. This paper investigates the change of frequency characteristics of two rectangular composite (carbon-epoxy) plates after inflicting structural damage. Following the necessary preparation of the structure's upper surfaces by white-and-black stochastic pattern, the responses (free vibratory movement) of structures to momentary excitation were recorded by an optical, contactless 3D digital image correlation (DIC) system that contains a set of ultrafast cameras. In order to determine the natural frequencies of the plates, the recorded time-domain responses were post-processed, i.e. converted to the frequency domain by fast Fourier transform (FFT). The reduction in values of natural frequencies is observed on the damaged structures. The performed experiments demonstrate the applicability of the DIC method in the structural health monitoring of composite parts.

Three-dimensional printed plastic products developed through fused deposition modelling (FDM) take long-term mechanical loading in most industrial prototypes. This article focuses on the impact of the 3D printing parameters, type of thermal treatment and variation of characteristic dimensions of standard specimens on the tensile properties of poly(lactic acid) (PLA) material. Two mediums were used for thermal treatment: NaCl powder and plaster. The specimens immersed in NaCl powder were heated to the melting temperature of the filament (200 °C), while the processing of the plastered specimens was performed at a temperature of 100 °C. After treatment, the specimens were cooled at room temperature (25 °C), and the dimensions of the annealed and untreated specimens were controlled. The tensile test of the specimens was performed on the universal test machine. The response surface methodology (RSM) is employed to predict the tensile stress by undertaking input parameters. The analysis of variance (ANOVA) results revealed that the untreated specimens, orientation –45/45 and layer thickness of 0.1 mm had the highest tensile stress value. Thermal treatment in plaster showed a significant increase in tensile strength, while the best specimens were obtained after treatment in NaCl, and all refer to the –45/45 (0.1 mm) orientation.