The use of fiber-reinforced polymer (FRP) composite materials are continuously growing in civil infrastructure due to their high strength, low weight, and manufacturing flexibility. However, FRP is characterized by sudden failure and lacks ductility. When used in construction, gradual failure of FRP components is desired to avoid catastrophic structural collapse. Due to its mechanical orthotropy, the behavior of FRP relies significantly on fiber orientation and stacking sequence. In this paper, a novel multi-angled glass fiber reinforced polymer (GFRP) composite laminate showing pseudo ductile behavior is produced using 3D-printing. This is accomplished by varying fiber orientation angles, stacking sequence, and thickness of lamina. Single-angled GFRP composite specimens were 3D-printed with different fiber orientation angles of 0°, 12°, 24°, 30°, 45°, and 90° using continuous and fused filament techniques. The tension test results of the single-angled specimens were then used to aid the design of multi-angled laminate for potential progressive failure behavior. A 3D finite element (FE) model was developed to predict the response of the experimental results and to provide insight into the failure mechanism of the multi-angled laminate. The experimental observations and the FE simulations show the possibility of producing pseudo ductile FRP-by-design composite using 3D-printing technology, which leads the way to fabricate next-generation composites for civil infrastructure.

Textile reinforced concrete (TRC) has gained attention from the construction industry due to its light weight, high tensile strength, design flexibility, corrosion resistance, and remarkably long service life. Some structural applications that utilize TRC components include precast panels, structural repair, waterproofing elements, and façades. TRC is produced by incorporating textile fabrics into thin cementitious concrete panels. Premature debonding between the textile fabric and concrete due to improper cementitious matrix impregnation of the fibers was identified as a failure-governing mechanism. To overcome this performance limitation, in this study, a novel type of TRC is proposed by replacing the cement binder with a polymer resin to produce textile reinforced polymer concrete (TRPC). The new TRPC is created using a fine-graded aggregate, methyl methacrylate polymer resin, and basalt fiber textile fabric. Four different specimen configurations were manufactured by embedding 0, 1, 2, and 3 textile layers in concrete. Flexural performance was analyzed and compared with reference TRC specimens with similar compressive strength and reinforcement configurations. Furthermore, the crack pattern intensity was determined using an image processing technique to quantify the ductility of TRPC compared with conventional TRC. The new TRPC improved the moment capacity compared with TRC by 51%, 58%, 59%, and 158%, the deflection at peak load by 858%, 857%, 3264%, and 3803%, and the toughness by 1909%, 3844%, 2781%, and 4355% for 0, 1, 2, and 3 textile layers, respectively. TRPC showed significantly improved flexural capacity, superior ductility, and substantial plasticity compared with TRC.

The fiber/matrix interface is a critical item that affects Fiber Reinforced Polymer (FRP) composites mechanical performance due to its control of the load transfer mechanism. Partially bonded interfaces have been shown to affect the failure mode of FRP composites. This article examines the significance of manipulating the fiber/matrix interfacial bond in 3D printed FRP composites on the mechanical performance of multilayer 3D printed FRP composites. Three designs are investigated with different fiber stacking sequences, fiber orientation, and interfacial bond configurations. The designs have a low coefficient of variation in load fractions between layers to enable a gradual load transfer and progressive failure. Utilizing 3D printer chamber temperature changes, a composite with a controlled bond configuration is achieved using thermal blocks. It was observed that the controlled bond configurations resulted in promoting progressive failure and increased the strain at failure of 3D printed FRP composites. The observations of direct tension tests were supported with interlayer shear strength and interfacial adhesion tests which explained the weakened load transfer in the thermal block configurations. Using the interface manipulation strategy with thermal blocks in 3D printed specimens, a 25% lower interlayer shear strength and a 65% lower interfacial adhesion was achieved compared with un-modified interfaces. These changes attribute to the altered load transfer mechanism in 3D printed glass fiber reinforced composites and high strain to failure of up to 5% using high strength high stiffness fiber orientations. This work does not incorporate any new materials into the thermoplastic-fiber 3D printed structure which has been the strategy of past work to modify mechanical performance. Alternatively, a unique approach by using chamber and print bed temperature characteristics to modify the interfacial bond has been adopted that has shown to promote progressive failures and improve ductility in FRP composites. This study furthers the development of ductile designs in FRP composites with 3D printing technology in aerospace, wind, infrastructure, and automobile applications.

Over the last century, the seismic behavior of reinforced concrete (RC) beam–column joints has drawn many researchers’ attention due to their complex stress state. Such joints should possess sufficient capacity and ductility to ensure integrity and safety when subjected to cyclic loading during seismic events. In the literature, while most studies have focused on the behavior of concentric beam–column joints, few studies investigated the response of eccentric beam–column joints, in which the beam’s centerline is offset from the centerline of the column. Recent earthquakes demonstrated severe damage in eccentric beam–column joints due to their brittle torsional behavior, which may threaten the ductility required for the overall structural performance. To investigate the effect of brittle failure on the strength, ductility, and stability of eccentric beam–column joints, nonlinear finite element (FE) models were developed and validated. The FE model was employed to study the effect of some geometric parameters on the global and local behaviors of beam–column joints, including the joint type (exterior and interior), the column aspect ratio, and the joint aspect ratio. The results show that the joint aspect ratio, which is the ratio of beam-to-column depth, has a predominant effect on the failure behavior of the joint. Additionally, the increase in column aspect ratio alters the failure mode from brittle joint shear failure to ductile beam-hinge, although there is an increase in the joint torsional moment. The current study also showed that interior joints exhibited a higher out-of-plane moment as well as more extensive column torsion cracks compared to exterior joints.