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.

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.

Optimization of molding process parameters for CF/PEEK composites based on Taguchi method

In this article, nine groups of laminates were prepared according to the Taguchi L9(33) test array to study the influence of three process parameters, including molding pressure, molding temperature, and holding time on the performance of unidirectional carbon fiber/polyetheretherketone (CF/PEEK) laminates. A differential scanning calorimetry test was employed to select a reasonable process parameters range. The transverse tensile strength of the laminates was measured, and the fiber–matrix interfacial bonding behavior of the tested samples was analyzed by scanning electron microscopy. The results showed that the significance of factors to transverse tensile strength were molding temperature, holding time, and molding pressure in sequence. The optimal molding process parameters for CF/PEEK composite laminate were molding temperature of 400°C, molding pressure of 3 MPa, and holding time of 30 min. The optimization results were meaningful for the extension and application of thermoplastic composites.

Effects of Fiber Angle on the Tensile Properties of Partially Delignified and Densified Wood

Partial delignification and densification provide a pathway to significant improvement in the mechanical performance of wood. In order to elucidate potential effects of this treatment on the mechanical anisotropy of wood, partially delignified and densified spruce wood veneers were characterized at varying degrees of off-axis alignment. While the tensile strength and the modulus of elasticity (MOE) were clearly improved in parallel to the axis of wood fibers, this improvement quickly leveled off at misalignment angles ≥30°. For transverse tensile strength, the performance of alkaline-treated and densified wood was even inferior to that of untreated wood. Microscopic examination revealed the presence of microscopic cracks in treated wood, which are assumed to be responsible for this observation. It is concluded that impaired transverse tensile properties are a weakness of partially delignified and densified wood and should be considered when a potential usage in load-bearing applications is intended.

Experimental reexamination of transverse tensile strength for IM7/8552 tape-laminate composites

Due to the observed dependence of transverse-tensile strength, Y T, on test geometry and specimen size, there is no consensus regarding a test method that can uniquely measure Y T. This study reexamines the characterization of Y T by comparing results from established flexure tests with results from a new tensile test that exhibits consistent failure in the gage region. Additionally, the effects of surface preparation and direction of transverse fracture are investigated. Results show that Y T is inversely proportional to specimen volume and surface roughness and is insensitive to direction of transverse fracture. The relationship between specimen volume and Y T is adequately captured by Weibull strength-scaling theory, except at the tails of the Y T distributions. However, specimens exhibited microcracking prior to failure, which violates the “weak-link” assumption of the Weibull theory. These findings highlight the challenges of using deterministic Y T values in progressive damage analysis.