No abstract

The current study explores the effects of geometrical shapes of the infills on the 3D printed polylactic acid (PLA) plastic on the tensile properties. For this purpose, by utilizing an accessible supply desktop printer, specimens of diamond, rectangular, and hexagonal infill patterns were produced using the fused filament fabrication (FFF) 3D printing technique. Additionally, solid samples were printed for comparison. The printed tensile test specimens were conducted at environmental temperature, Ta of 23 °C and crosshead speed, VC.H of 5 mm/min. Mainly, this study focuses on investigating the percentage infill with respect to the cross-sectional area of the investigated samples. The mechanical properties, i.e., modulus of toughness, ultimate tensile stress, yield stress, and percent elongation, were explored for each sample having a different geometrical infill design. The test outcomes for each pattern were systematically compared. To further validate the experimental results, a computer simulation using finite element analysis was also performed and contrasted with the experimental tensile tests. The experimental results mainly suggested a brittle behavior for solidly infilled specimen, while rectangular, diamond, and hexagonal infill patterns showed ductile-like behavior (fine size and texture of infills). This brittleness may be due to the relatively higher infill density results that led to the high bonding adhesion of the printed layers, and the size and thickness effects of the solid substrate. It made the solidly infilled specimen structure denser and brittle. Among all structures, hexagon geometrical infill showed relative improvement in the mechanical properties (highest ultimate tensile stress and modulus values 1759.4 MPa and 57.74 MPa, respectively) compared with other geometrical infills. Therefore, the geometrical infill effects play an important role in selecting the suitable mechanical property’s values in industrial applications.

The behavior of crack growth of polymeric materials is affected by several operating conditions such as crosshead speed, specimen thickness, load line, and specimen configurations, which reverse the behavior of crack from stable to unstable crack growth behavior. The main objective of the present paper is the determination of plane strain fracture toughness (KIC) for polyvinyl chloride (PVC) used in piping water transmission systems. The dimensions of the PVC pipe are outside diameter, Do = 315 mm, standard dimensions ratio, SDR = 13.23, ratio between outside to inside radii Ro/Ri = 1.179, and pipe thickness, t = 24 mm. Curved specimens are prepared from a pipe by cutting 12 mm thickness ring segments. The curved specimens are divided into two specimen configurations, namely, curved three-point bend (CTPB) and C-shaped tension (CST) specimens. All specimens are provided artificially with a precrack. CTPB specimen is further cut into five 72 deg sectors with each being centrally notched to a depth approximately a = 0.479 of the wall thickness. CST specimen configuration is characterized by the eccentricity X = 0, and 0.5 W, of the loading holes from the bore surface. The linear elastic fracture mechanics theory (LEFM) is used to predict the plane strain fracture. The tests are carried out at room temperature, Ta equal 20 °C, and different crosshead speeds of (10–500 mm/min). The numerical analysis carried out within the frame of the present work is done using the finite element program Cosmos 2.6. Finite element method (FEM) is used to compute the stress intensity factor KQ surrounding the crack tip. The computed stress intensity factor can then be compared with that obtained by theoretical equation. The experimental fracture test results reveal that the crosshead speed has been proven to affect the mode of failure and mode of fracture. At lower crosshead speeds, the mode of failure is ductile, while at higher crosshead speeds, it is brittle. The specimen configuration also affects the fracture toughness. CST specimens show higher fracture toughness in the case of pin loading location X = 0.5W than X = 0 by about (12%). The transitional crosshead speed is affected by specimen geometry. CST specimens (CST) at X = 0 and 0.5W have higher transitional crosshead speed compared with the CTPB specimen configuration.