Verification of a fracture model for fiber reinforced concrete beams in bending

In this study, digital light processing (DLP) was used to achieve 3D-printed composite materials containing photosensitive resin blended with starch and hemp fibers. The synthesis of 3D-printed composites was performed without heating, according to various material combinations ranging from pure photosensitive resin to a mixture of three phases, including resin, starch, and hemp fibers, with the weight content for each reinforcing phase reaching up to a third of the formulation. The morphology, composition, and structure of the 3D-printed composites were assessed using infrared spectroscopy, laser granulometry, X-ray diffraction, and optical and scanning electron microscopy. In addition, thermal behavior and mechanical performance were studied using calorimetry, differential scanning calorimetry, and tensile testing combined with high-speed optical imaging. The results showed that the post-curing step is a leading factor for improving the mechanical performance of the 3D-printed composites. In addition, hemp fiber or starch did not alter the tensile strength. However, the largest reinforcing effect in terms of stiffness improvement was obtained with starch. Additionally, starchy composites demonstrated the strongest dependence of heat capacity on operating temperature.

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Synthesis of a Starchy Photosensitive Material for Additive Manufacturing of Composites Using Digital Light Processing

In this paper, the influence of the infill volume percentage on fatigue life and failure types of 3D-printed gears made of polylactic acid (PLA) is studied. The experiments were conducted using a custom-made gear testing device, where the specimens were tested at the same torque and rotational speed. It has been shown that the fatigue life of gears made of PLA increases significantly with the increase in infill volume percentage. Different types of gear failures have been observed depending on the volume percentage. 

Experimental failure analysis of polylactic acid gears made by additive manufacturing

Material behavior modeling for additive manufacturing (AM) technology represents a challenge because the manufacturing process and post-processing parameters strongly influence the mechanical properties of the part. Photoelasticity is a well-known full-field optical technique used for direct stress/strain determination and design evaluation purposes. A novel use of digital light processing (DLP), a form of vat polymerization AM technologies in photoelastic specimen production is discussed in this paper. A number of preliminary experiments were undertaken to address critical issues related to DLP process. It was concluded that the UV exposure time, dependent mostly on layer thickness, and orientation are the main factors affecting the mechanical properties and the accuracy of the printed samples. Pure bending test was used to determine mechanical and photoelastic properties of a commercially available acrylic-based photopolymer, not previously reported in the literature. The rectangular beam sample used was built in vertical layer orientation and fully-cured. The estimated value of Young’s modulus was within the expected range for acrylics, and the photoelastic constant obtained provides increased confidence in the investigated acrylic polymer for photoelastic stress analysis purposes, and consequently for validation of computer-based models.

Maja Dundović

Papers

Digital light processing in photoelastic models production for material behavior modeling

Digital light processing in photoelastic models production for material behavior modeling