Using the Area of Contact between Layers as a Predictor for the Anisotropic Strength of Parts Produced by FDM

Fused Filament Fabrication (FFF), better known as FDM© (Fused Deposition Modeling) is an additive manufacturing process (AM) by which a physical object can be created from a 3D model generated in the computer, through layer-by-layer deposition of semi-melted plastic filaments. However, parts produced by the FDM process have different characteristics compared to parts produced by traditional methods such as plastic injection, especially with regard to mechanical properties related to stresses (tensile, compression, torsion and shear), due to the anisotropic nature of the process deposition. Many works have been carried out in order to determine the influence between the FDM process parameters and the mechanical characteristics of parts produced by this technology. Traditionally, the studied parameters comprise those that are adjusted in slicing software, which does not satisfactorily reflect the bond between the layers. This work uses the area of contact between the layers as the determining factor of the transverse tensile strength to bedding and suggests a methodology for the determination of this parameter. Using analysis of variance (ANOVA) and the Taguchi analysis method, we identified the contact area between the layers as the most relevant parameter for tensile strength in the transverse direction of the printed layers with a relevance of more than 95% over the others investigated parameters. From the survey of relevant properties, new tests were carried out to determine a mathematical model to predict the minimum slicing parameters that should be used to obtain the required strength. Keywords: Fused Deposition Modeling, Mechanical Strength, AM Anisotropic Property, Layer Bond Properties, PLA.

Microstructure and Mechanical Properties of Friction Stir-Welded Dissimilar Joints of ZK60 and Mg-4.6Al-1.2Sn-0.7Zn Alloys

In order to clarify the microstructural evolution and the mechanical property of dissimilar friction stir-welded joints of ZK60 and Mg-4.6Al-1.2Sn-0.7Zn magnesium alloys, two types of arrangement with ZK60 at advancing side (AS) or retreating side (RS) were adopted. The macrostructure and the microstructure of the dissimilar welded joints were discussed, and the microhardness and the transverse tensile properties of the joints were measured. There are three stirring sub-zones with different compositions and two clear interfaces within the joints. Due to the effect of both the original grain size of base materials and the growth of recrystallized grains, in the stir zone (SZ), the grain size of ZK60 increased slightly, while the grain size of Mg-4.6Al-1.2Sn-0.7Zn decreased significantly. The dissolution of precipitates was gradually significant from RS to AS within the SZ due to the gradual increase in strain and heat. The grain refinement led to an increase in hardness, while the dissolution of precipitates resulted in a decrease in hardness. The performance of the joints obtained with ZK60 placed on the RS is slightly better than that of that on the AS. The tensile fracture of both joints occurred at the interface between SZ and the thermos-mechanical affected zone at the AS, and showed a quasi-dissociative fracture.

A New-Type Semi-Rigid Base Layer Structure for Long Service Life Pavement

Targeting at the problem of pavement cracking under long-term load, this study developed a new-type semi-rigid base layer structure based on the CGC (cement stabilized macadam - graded broken stone - cement stabilized macadam) combinations, and used ANSYS to simulate this proposed structure under conditions of different modulus combinations, deflection under different thickness, different vertical strain values on the top surface of roadbed, and different transverse tensile stress values of bottom base layer. The simulation results indicate that, the various mechanical properties of the proposed new structure can well meet the specifications, and the time of crack generation has been slowed down; the use of graded broken stone in the proposed structure has achieved both the purposes of saving construction cost and reducing construction difficulty. By reasonably controlling the CGC structure and modulus, this study has successfully suppressed the generation of reflection cracks, which can provide good theoretical evidence for prolonging the service life of semi-rigid base layer pavement.

Three-dimensional strain analysis of asphalt pavement based on vehicle–pavement model of interaction

This study analyzes the 3D (3D) strain on a pavement by using a model of a vehicle with seven degrees of freedom and that of a road in elastic half-space by using the finite element software ANSYS. The results are as follows: The 3D strain on the two wheels along the centerline was significantly influenced by the superposition of the wheel, and the 3D strain under a single wheel was far higher than that along the centerline of two wheels, and represented the most unfavorable position on the road. The vertical strain consisted mainly of compressive strain at different depths, and that at the bottom of the pavement was slightly higher than that on top. The longitudinal and transverse strains were all compressive strains on top of the pavement and tensile strains at the bottom, respectively. The longitudinal and transverse strains both on top and at the bottom of the pavement were similar. The authors then analyzed the influence of the thickness of the pavement, its modulus, and equivalent resilient modulus on the vertical compressive strain, longitudinal tensile strain, and transverse tensile strain in case of a single wheel. Furthermore, a model to predict the 3D strain under the comprehensive effect of the structural parameters of the road was established. It can provide the basis and a reference for the design, construction, fault detection, and maintenance of roads.

REACTIVE EXTRUSION ADDITIVE MANUFACTURING OF A SHORT FIBER REINFORCED THERMOSET COMPOSITE

Additive manufacturing (AM) of high-performance composites has gained increasing interest over the last few years. Commercially available AM technologies often use thermoplastics as they are easy to process, i.e., to melt and re-solidify. However, thermosetting polymers generally achieve superior mechanical properties and thermostability. This study investigates reactive extrusion additive manufacturing (REAM) of a thermosetting polymer reinforced with carbon fibers. The process utilizes highly exothermic and fast curing resin/catalyst systems, eliminating the need for post-curing. The rheological properties of the liquid resin are first tuned for REAM using ~2wt.% fumed silica and ~10vol.% milled carbon fibers. Then, a robotic arm is used to print the composite samples. The coupons’ longitudinal and transverse tensile properties are measured and correlated with the degree of cure, porosity, fiber length distribution, and fiber orientation distribution. The incorporation of milled carbon fibers, 50-200 m long, primarily affects the stiffness. Compared to neat polymer parts, carbon fiber reinforced composites are 51% stiffer and 8% stronger. In addition, polymeric crosslinking between part layers resulted in strong inter-layer bonding. Short fibers were also randomly oriented within parts due to the nozzle size and shape, resulting in nearly isotropic parts. The results presented here pave the road for fast and low-energy AM of high-performance composites.

Strength Characteristics of 3D-Printed PETG-Based Products Optimization

The paper considers the dependence of the strength properties of 3D-printed parts on FDM printing modes (temperature and speed), as well as the layer arrangement. PETG (polyethylene glycol terephthalate) based filament was chosen as the basis. A 3D printer was used to produce samples with strictly defined orientation of layers — longitudinal and transverse tensile force at different temperature and printing speed. The experiment has established the effect of these two factors on the tensile strength. The strength of the samples printed transversely was higher than the strength of samples printed longitudinally. This indicates a higher interlayer adhesion.

Induction Assisted Hybrid Friction Stir Welding of Dissimilar Materials AA5052 Aluminium Alloy and X12Cr13 Stainless Steel

This research aimed to study the induction in-situ heated hybrid friction stir welding (IAFSW) method to join AA5052 aluminium alloy with X12Cr13 stainless steel (SS) to enhance joint strength. The potency of this method on the mechanical properties and microstructural characterizations were also investigated. The results show that the transverse tensile strength gained was 94% of the AA5052 base metal that is 229.5 MPa. This superior strength was achieved due to the annealing that happened to the AA 5052 region and elevated plastic flow in the weld zone by the in-situ induction heating, which resulted in the elongation of the weld region. The microstructure characterization indicates that a refined grain structure was gained in the nugget zone without defects.