Anisotropic Mechanical Properties of ABS Parts Fabricated by Fused Deposition Modelling

In recent years, layered manufacturing (LM) processes have begun to progress from rapid prototyping techniques towards rapid manufacturing methods, where the objective is now to produce finished components for potential end use in a product (Caulfield et al., 2007). LM is especially promising for the fabrication of specific need, low volume products such as replacement parts for larger systems. This trend accentuates the need for a thorough understanding of the associated mechanical properties and the resulting behavior of parts produced by layered methods. Not only must the base material be durable, but the mechanical properties of the layered components must be sufficient to meet in-service loading and operational requirements, and be reasonably comparable to parts produced by more traditional manufacturing techniques. This chapter presents the details of a study completed to quantitatively analyze the potential of fused deposition modelling to fully evolve into a rapid manufacturing tool. The project objective is to develop an understanding of the dependence of the mechanical properties of FDM parts on raster orientation and to assess whether these parts are capable of maintaining their integrity while under service loading. The study examines the effect of fiber orientation, i.e. the direction of the polymer beads relative to the loading direction of the part, on a variety of important mechanical properties of ABS components fabricated by fused deposition modeling. Tensile, compressive, flexural, impact, and fatigue strength properties of FDM specimens are examined, evaluated, and placed in context in comparison with the properties of injection molded ABS parts

Influence of Impact Conditions on Feedstock Deposition Behavior of Cold-Sprayed Fe-Based Metallic Glass

Cold spray is a promising method by which to deposit dense Fe-based metallic glass coatings on conventional metal substrates. Relatively low process temperatures offer the potential to prevent the crystallization of amorphous feedstock powders while still providing adequate particle softening for bonding and coating formation. In this study, Fe48 Mo14 Cr15 Y2 C15 B6 powder was sprayed onto a mild steel substrate, using a variety of process conditions, to investigate the feasibility of forming well-bonded amorphous Fe-based coatings. Particle splat adhesion was examined relative to impact conditions, and the limiting values of temperature and velocity associated with successful softening and adhesion were empirically established. Variability of particle sizes, impact temperatures, and impact velocities resulted in splat morphologies ranging from well-adhered deformed particles to substrate craters formed by rebounded particles and a variety of particle/substrate interface conditions. Transmission electron microscopy studies revealed the presence of a thin oxide layer between well-adhered particles and the substrate, suggesting that bonding is feasible even with an increased oxygen content at the interface. Results indicate that the proper optimization of cold spray process parameters supports the formation of Fe-based metallic glass coatings that successfully retain their amorphous structure, as well as the superior corrosion and wear-resistant properties of the feedstock powder

Processing and Composition Effects on the Fracture Behavior of Spray-Formed 7XXX Series Al Alloys

The fracture properties of high-strength spray-formed Al alloys were investigated, with consideration of the effects of elemental additions such as zinc,manganese, and chromium and the influence of the addition of SiC particulate. Fracture resistance values between 13.6 and 25.6 MPa (m)1/2 were obtained for the monolithic alloys in the T6 and T7 conditions, respectively. The alloys with SiC particulate compared well and achieved fracture resistance values between 18.7 and 25.6 MPa (m)1/2. The spray-formed materials exhibited a loss in fracture resistance (KI) compared to ingot metallurgy 7075 alloys but had an improvedperformance compared to high-solute powder metallurgy alloys of similar composition. Characterization of the fracture surfaces indicated a predominantly intergranular decohesion, possibly facilitated by the presence of incoherent particles at the grain boundary regions and by the large strength differentialbetween the matrix and precipitate zone. It is believed that at the slip band-grain boundary intersection, particularly in the presence of large dispersoids and/or inclusions, microvoid nucleation would be significantly enhanced. Differences in fracture surfaces between the alloys in the T6 and T7 condition were observed and are attributed to inhomogeneous slip distribution, which results in strain localization at grain boundaries. The best overall combination of fracture resistance properties were obtained for alloys with minimum amounts of chromium and manganese additions

Numerical investigation of the influence of transverse welds on the strength of aluminum alloy I-Shaped members: Columns

This paper presents a numerical investigation, using finite element analysis, of the effects of transverse welds on the structural behavior of aluminum-alloy compression members. A non-linear finite element (FE) model was developed, and validated using experimental tests, to simulate the behavior of 6061-T6 aluminum-alloy columns with an I-shaped AW6x4.03 section geometry. The FE model included different material properties for the heat-affected zone (HAZ) that occurs in the proximity of the weld and the remaining base material, and incorporated both geometric and material nonlinearities. A parametric study of 80 columns with and without transverse welds was conducted, which investigated ten unbraced lengths, three weld centerline locations along the member length, and two types of post-yield material stiffness models, including elastic-perfectly plastic and strain hardening materials. The FE results provide clear evidence of the significance of the HAZ strength reduction on the load carrying capacity of welded aluminum-alloy columns. Numerical results were compared with those obtained using the provisions within the Aluminum Association’s Specification for Aluminum Structures, and they were used to develop proposed modifications to these provisions, which can remove the degree conservatism observed. A similar study on beams is presented in a companion paper

Formulation and Validation of Minimum Brace Stiffness For Systems of Compression Members

Bracing that is used to reduce the effective length of compressive members, and thereby increase their load carrying capacity, must be designed to provide adequate stiffness and strength. In practice, a targeted minimum or ideal brace stiffness is typically defined, and then this value is increased by a factor of two or three in order to ensure brace strength demands can be satisfied efficiently. While straightforward expressions are available to determine the ideal brace stiffness for single members, the brace stiffness for systems of multiple parallel compression members is more complex. This paper presents the derivation and validation of a simple mathematical expression that is useful for obtaining the ideal brace stiffness of structural systems composed of multiple parallel compression members or sub-assemblages. Use and validation of the proposed expression is explored through a variety of examples. Agreement with results obtained using finite element analyses suggests that the developed expression sufficiently determines the minimum bracing stiffness for systems of multiple parallel members with single and multiple brace points

Numerical Investigation of the Influence of Transverse Welds on the Strength of Aluminum Alloy I-Shaped Members – Beams

The weldability of high strength aluminum alloys is an important consideration when designing aluminum structures. While these alloys do suffer significant strength loss in the weld heat affected zone (HAZ), available design codes are often overly conservative in their guidelines regarding the design of welded aluminum members. This paper presents a numerical investigation of the effect of reduced strength in the HAZ adjacent to a transverse weld in simply-supported aluminum alloy beams subject to concentrated end moments. Nonlinear finite element (FE) models were developed, validated, and applied in a parametric study of non-welded and transversely welded 6061-T6 flexural members with an I-shaped cross section. The FE model included initial geometric imperfections and material nonlinearities in both the HAZ and the base material. The parametric study examined 400 unique beam cases defined by the combination of four factors, including slenderness ratio or unbraced length, weld location along the beam span, post-yield material stiffness model, and loading case or resulting moment gradient. The FE results were subsequently compared with capacities predicted by the Aluminum Association’s Specification for Aluminum Structures, with proposed modifications to SAS also provided. A similar study on columns is presented in a companion paper within this issue

Tensile and Fatigue Behavior of Layered Acrylonitrile Butadiene Styrene

Purpose - This paper aims to define the effect of specimen mesostructure on the monotonic tensile behavior and tensile-fatigue life of layered acrylonitrile butadiene styrene (ABS) components fabricated by fused deposition modeling (FDM). Design/methodology/approach - Tensile tests were performed on FDM dogbone specimens with four different raster orientations according to ASTM standard D638-03. Resulting ultimate tensile stresses (UTS) for each raster orientation were used to compute the maximum stress for fatigue testing, i.e. 90, 75, 60 and 50 or 45 per cent nominal values of the UTS. Multiple specimens were subjected to tension - tension fatigue cycling with stress ratio of R = 0.10 in accordance with ASTM standard D7791-12. Findings - Both tensile strength and fatigue performance exhibited anisotropic behavior. The longitudinal (0 degrees) and default (+45/-45 degrees) raster orientations performed significantly better than the diagonal (45 degrees) or transverse (90 degrees) orientations in regards to fatigue life, as displayed in the resulting Wohler curves. Practical implications - Raster orientation has a significant effect on the fatigue performance of FDM ABS components. Aligning FDM fibers along the axis of the applied stress provides improved fatigue life. If the direction of applied stresses is not expected to be constant in given application, the default raster orientation is recommended. Originality/value - This project provides knowledge to the limited work published on the fatigue performance of FDM ABS components. It provides S-N fatigue life results that can serve as a foundation for future work, combining experimental investigations with theoretical principles and the statistical analysis of data

Experimental Investigation of Torsional Strengths of Aluminum Alloys – Circular and Rectangular Solid Sections

An experimental investigation of aluminum alloy rods and bars subjected to torsional loading is presented. The test specimens were 6061-T6 and 5050-H32 alloys with solid circular and solid rectangular cross-sections. The test plan included torsion tests until rupture, for 5 sets of 6061-T6 specimens with circular and rectangular cross-sections, and 4 sets of 5050-H32 specimens with rectangular cross-sections. Each test series included six specimens, for a total of 54 torsion tests. Experimental torque and angular deformation data were recorded and subsequently analyzed to investigate the torsional stiffness, strength, and ductility of the specimens, including consideration of initial-yield, full-yield, and rupture strengths, as well as total angular deformation at failure. A methodology was developed to estimate the full plastic torque, associated with yielding throughout the cross-section, from the measured experimental data. Results were compared with nominal strengths predicted using the material properties required within the Aluminum Association’s Specification for Aluminum Structures (SAS). Use of these properties in conjunction with SAS’s first-yield criterion produced results that were overly conservative in general, demonstrating the importance of exploring changes to the Specification. Recommendations are made for adjustments and extensions to the SAS, which support an ultimate strength approach consistent with its strength limit states design methodology