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This paper aims to study the interfacial and interlayer bonding of Polylactic acid parts manufactured by fused deposition modelling. Different layer thicknesses are analysed in the manufacture of these pieces and the lack of material associated with this parameter is verified. The influence of the immersion of these parts in different solvents is also studied, as they are increasingly used in the improvement of the surface finish. Tomography results are also obtained in which the increase in density of the parts subjected to these treatments is demonstrated.

The material used in this study is a 1.75-mm diameter polylactic acid (PLA) filament from fused filament fusion world. Monolayer and multilayer samples have been manufactured. The manufactured parts were subjected to solvent immersion for a period of 60 s. The solvents used are chloroform (CHCl3), dichloromethane (CH2Cl2), tetrahydrofuran (C4H8O) and ethyl acetate (C4H8O2). The pieces were then dried for 48 h. The interior of the samples was evaluated by two techniques: microscopy and tomography.

With this study, it has been observed that the thickness of the layer affects the porosity interfacial to a greater extent than in the interlayer, causing the increase in porosity as this thickness is increased.The impact of different chemical treatments (immersions in different solvents) on the internal quality of the parts has been evaluated. All the solvents analysed soften the surface as they cause the softening of the material and its possible redistribution. In the interior, however, they affect in a lighter way. The retention of solvents in the porosity of the pieces is also checked, especially pronounced in the areas close to the surface. Finally, changes are observed in the density of the pieces, related to the partial crystallization of the samples.

All that has been studied shows that the application of chemical post-processes not only affects the surface texture of the parts, or the less studied mechanical properties, but also affects the interfacial union of the parts in a very different way. This is the first study carried out on this aspect with polylactic acid (PLA) and post-processing methods.

The material extrusion (ME) process induces variations in the final part’s microscopic and macroscopic structural characteristics. This viewpoint article aims to uncover the relation between ME fabrication parameters and the microstructural and mesostructural characteristics of the ME BASF Ultrafuse Steel 316L metal parts. These characteristics can affect the structural integrity of the produced parts and components used in various engineering applications.

Recent studies on the ME BASF Ultrafuse Steel 316L are reviewed, with a focus on those which report microstructural and mesostructural characteristics that may affect structural integrity.

A relationship between ME fabrication parameters and subsequent microstructural and mesostructural characteristics is discussed. Common microstructural and mesostructural/macrostructural defects are also highlighted and discussed.

This viewpoint article attempts to bridge the existing gap in the literature, highlighting the influence of ME fabrication parameters on Steel 316L parts fabricated via this additive manufacturing method. Moreover, this article identifies and discusses important considerations for the purposes of selecting and optimising the structural integrity of ME-fabricated Steel 316L parts.

The mechanical and tribological properties of polymers and polymer composites vary with different environmental conditions. This paper aims to review the influence of humidity/water conditions on various polymers and polymer composites' mechanical properties and tribological behaviors.

The influence of humidity and water absorption on mechanical and tribological properties of various polymers, fillers and composites has been discussed in this paper. Tensile strength, modulus, yield strength, impact strength, COF and wear rates of polymer composites are compared for different environmental conditions. The interaction between the water molecules and hydrophobic polymers is also represented.

Pure polymer matrices show somewhat mixed behavior in humid environments. Absorbed moisture generally plasticizes the epoxies and polyamides and lowers the tensile strength, yield strength and modulus. Wear rates of PVC generally decrease in humid environments, while for polyamides, it increases. Fillers like graphite and boron-based compounds exhibit low COF, while MoS2 particulate fillers exhibit higher COF at high humidity and water conditions. The mechanical properties of fiber-reinforced polymer composites tend to decrease as the rate of humidity increases while the wear rates of fiber-reinforced polymer composites show somewhat mixed behavior. Particulate fillers like metals and advanced ceramics reinforced polymer composites exhibit low COF and wear rates as the rate of humidity increases.

The mechanical and tribological properties of polymers and polymer composites vary with the humidity value present in the environment. In dry conditions, wear loss is determined by the hardness of the contacting surfaces, which may not effectively work for high humid environments. The tribological performance of composite constituents, i.e. matrix and fillers in humid environments, defines the overall performance of polymer composite in said environments.

The purpose of this study is to propose the use of a pre-deposition heating system for fused filament fabrication (FFF) as a means to enhance interlayer bonding by elevating the substrate temperature. The effects of the heating on thermal profile at the bonding interface and the mechanical properties of three-dimensional printed parts are investigated.

A 12-W laser head is integrated to a commercial printer as the pre-deposition heating system. The laser beam heats up substate before the deposition of a fresh filament. Effects of laser powers are investigated and the thermal profile is measured with thermocouple, infrared camera and finite element model. The correlation between the temperature at the bonding interface and the bonding quality is investigated by conducting tensile testing and neck width measurement with microscope.

The pre-deposition heating system is proven to be effective in enhancing the inter-layer strength in FFF parts. Tensile testing of specimens along build direction (Z) shows an increase of around 50% in ultimate strength. A linear relationship is observed between the pre-deposition temperature at bond interface and bonding strength. It is evident that elevating the pre-deposition temperature promotes interlayer polymer diffusion as shown by the increased neck width between layers.

Thermocouples that are sandwiched between layers are used to achieve accurate measurement of the interfacial temperature. The temperature profiles under pre-deposition heating are analyzed and correlated to the interlayer bonding strengths.

This study aims to focus on the effect of interlayer bonding and thermal decomposition on the mechanical properties of fused filament fabrication-printed polylactic acid specimens at high extrusion temperatures.

A printing process, that is simultaneous manufacturing of contour and specimen, is used to improve the printing accuracy at high extrusion temperatures. The effects of the extrusion temperature on the mechanical properties of the interlayer and intra-layer are evaluated via tensile experiments. In addition, the microstructure evolution affected by the extrusion temperature is observed using scanning electron microscopy.

The results show that the extrusion temperature can effectively improve the interlayer bonding property; however, the mechanical properties of the specimen for extrusion temperatures higher than 270°C may worsen owing to the thermal decomposition of the polylactic acid (PLA) material. The optimum extrusion temperature of PLA material in the three-dimensional (3D) printing process is recommended to be 250–270°C.

A temperature-compensated constitutive model for 3D printed PLA material under different extrusion temperatures is proposed. The present work facilitates the prediction of the mechanical properties of specimens at an extrusion temperature for different printing temperatures and different layers.

This work aims to develop a new kind of semicrystalline polymer filament and optimize its printing parameters in the fused deposition modeling process. The purpose of this work also includes producing FDM parts with good ductility.

A new kind of semicrystalline filaments composed of long-chain polyamide (PA)1012 was prepared by controlling screw speed and pulling speed carefully. The optimal printing parameters for PA1012 filaments were explored through investigating dimensional accuracy and bonding strength of FDM parts. Furthermore, the mechanical properties of PA1012 specimens were also evaluated by varying nozzle temperatures and raster angles.

It is found that PA1012 filaments can accommodate for FDM process under suitable printing parameters. The print quality and mechanical properties of FDM parts highly depend on nozzle temperature and bed temperature. Even though higher temperatures facilitate stronger interlayer bonding, FDM parts with excellent tensile strength were obtained at a moderate nozzle temperature. Moreover, a bed temperature well above the glass transition temperature of PA1012 can eliminate shrinkage and distortion of FDM parts. As expected, FDM parts prepared with PA1012 filaments exhibit good ductility.

Results in this work demonstrate that the PA1012 filament allows the production of FDM parts with desired mechanical performance. This indicates the potential for overcoming the dependence on amorphous thermoplastics as a feedstock in the FDM technique. This work also provides insight into the effect of materials properties on the mechanical performance of FDM-printed parts.

Extrusion width, the width of printed filaments, affects multiple critical aspects in mechanical properties in material extrusion additive manufacturing: filament geometry, interlayer load-bearing bonded area and fibre orientation for fibre-reinforced composites. However, this study aims to understand the effects of extrusion width on 3D printed composites, which has never been studied systematically.

Four polymers with and without short-fibre reinforcement were 3D printed into single-filament-wide specimens. Tensile properties, mechanical anisotropy and fracture mechanisms were evaluated along the direction of extruded filaments (F) and normal to the interlayer bond (Z). Extrusion width, nozzle temperature and layer height were studied separately via single-variable control. The extrusion width was controlled by adjusting polymer flow in the manufacturing procedure (gcode), where optimisation can be achieved with software/structure design as opposed to hardware.

Increasing extrusion width caused a transition from brittle to ductile fracture, and greatly reduced directional anisotropy for strength and ductility. For all short fibre composites, increasing width led to an increase in strain-at-break and decreased strength and stiffness in the F direction. In the Z direction, increasing width led to increased strength and strain-at-break, and stiffness decreased for less ductile materials but increased for more ductile materials.

The transformable fracture reveals the important role of extrusion width in processing-structure-property correlation. This study reveals a new direction for future research and industrial practice in controlling anisotropy in additive manufacturing. Increasing extrusion width may be the simplest way to reduce anisotropy while improving printing time and quality in additive manufacturing.

This paper aims to study the features of microstructures and mechanical properties of the joints which were produced by transient liquid phase method. The difference between phases in bonding region identified through metallography pictures and applying hardness and shear strength tests.

The bonding process was carried out at a temperature of 300°C for time durations ranging from 15 to 120 min. The scanning electron microscopy equipped with energy dispersive spectroscopy system and optical microscopy were used to examine microstructural characteristics, and mechanical properties of the joints were studied by applying microhardness and shear tests. The shear tests were conducted by a shear fixture which was mounted on the tensile machine.

The intermetallic compounds of the Cu₆Sn₅ −η and the Cu₃Sn-ε were formed simultaneously in the bonding interface. Although the η-phase, which exhibits scallop-shaped morphology, grows very quickly, upon completion of the isothermal solidification stage, it turns into the ε-phase. The hardness of the bonding interface is significantly higher than that of the substrate. The shear results show that once the bonding process is complete, brittle fracture occurs. Moreover, a greater decrease in strength was observed when the ε-phase is the only phase in the bonding region.

The hardness number of the η-phase is higher than that of the ε-phase. The hardness numbers of the η-phase and the ε-phase are 894 and 689 HV, respectively. The mean shear strength values of the samples that were bonded at 300 °C for 15, 60 and 120 min were 11.7, 9.5 and 5.4 MPa, respectively.

This study/paper aims to develop fundamental understanding of mechanical properties for multiple fibre-reinforced materials by using a single-filament-wide tensile-testing approach.

In this study, recently validated single-filament-wide tensile-testing specimens were used for four polymers with and without short-fibre reinforcement. Critically, this specimen construct facilitates filament orientation control, for representative longitudinal and transverse composite directions, and enables measurement of interlayer bonded area, which is impossible with “slicing” software but essential in effective property measurement. Tensile properties were studied along the direction of extruded filaments (F) and normal to the interlayer bond (Z) both experimentally and theoretically via the Kelly–Tyson model, bridging model and Halpin–Tsai model.

Even though the four matrix-material properties varied hugely (1,440% difference in ductility), consistent material-independent trends were identified when adding fibres: ductility reduced in both F- and Z-directions; stiffness and strength increased in F but decreased or remained similar in Z; Z:F strength anisotropy and stiffness anisotropy ratios increased. Z:F strain-at-break anisotropy ratio decreased; stiffness and strain-at-break anisotropy were most affected by changes to F properties, whereas strength anisotropy was most affected by changes to Z properties.

To the best of the authors’ knowledge, this is the first study to assess interlayer bond strength of composite materials based on measured interlayer bond areas, and consistent fibre-induced properties and anisotropy were found. The results demonstrate the critical influence of mesostructure and microstructure for three-dimensional printed composites. The authors encourage future studies to use specimens with a similar level of control to eliminate structural defects (inter-filament voids and non-uniform filament orientation).

In friction welding of dissimilar joint method, few material compositions are not possible to weld effectively. For better dissimilar metal joining in friction welding, the interlayer techniques are used by the third metal to increase the diffusion for suitable metal bonding. The interlayer metals are popularly held by coating, foils, sheet and solid rod form. The coating method needs more care for surface preparation with special coating equipment with high workmanship. In case of foil as intermediate metal, more care is neededfor holding between the metal; most of the time this technique has the possibility of failure by peeling off from the contact surface during high speed rotation with pressure during friction generation.

In this investigation, a copper coin was machined to a suitable size (transition fit) to suit the recess inside the SS rod. The mating surfaces of Cu coin, SS rod and Ti alloy were machined, polished to mirror finish and handled in friction welding machine. The purpose of the transition fit between the coin and SS rod is for holding the same intact before the beginning of the process.

Successful joint was achieved with good joint strength at less time. Empirical models were established to fin out the joint strength at any given parameter within the range of investigation

The models developed can be used only within the range of investigation considered for experimentation.

The paper includes implications for the development of a method of joining any dissimilar joints

In this investigation, a copper coin was machined to a suitable size (transition fit) to suit the recess inside the SS rod. The mating surfaces of Cu coin, SS rod and Ti alloy were machined, polished to mirror finish and handled in friction welding machine. The purpose of the transition fit between the coin and SS rod is for holding the same intact before the beginning of the process.