Effects of extruder temperatures and raster orientations on mechanical properties of the FFF-processed polylactic-acid (PLA) material

Purpose The purpose of this study is to investigate the influences of extruder temperatures and raster orientations on the mechanical properties of polylactic-acid (PLA) material processed by using fused filament fabrication (FFF). Design/methodology/approach In this research, the PLA specimens were first printed with nozzle or extruder temperatures of 205°C, 215°C and 225°C and then evaluated in terms of their physical, chemical and mechanical properties. An appropriate extruder temperature was then selected based on this experiment and used for the printing of the other PLA specimens having various raster orientations. A series of tensile tests were carried out again to investigate the influence of raster orientations on the tensile strength, tensile strain and elastic modulus of those FFF-processed PLA materials. In the end, the one-way ANOVA was applied for the statistical analysis and the Mohr’s circle was established to aid in the analysis of the data obtained in this experiment. Findings The result of this study shows that the chemistry, porosity, degree of crystallinity and mechanical properties (tensile strength, strain and elastic modulus) of the PLA material printed with a raster angle of 0° were all insensitive to the increasing extruder temperature from 205°C to 225°C. Meanwhile, the mechanical properties of such printed PLA material were obviously influenced by its raster orientation. In this case, a PLA material with a raster orientation parallel to its loading axis, i.e. those with a raster angle of θ = 0°, was found as the strongest material. Meanwhile, the raster configuration-oriented perpendicular to its loading axis or θ = 90° yielded the weakest PLA material. The results of the tensile tests for the PLA material printed with bidirectional raster orientations, i.e. θ = 0°/90° and 45°/−45° demonstrated their strengths with values falling between those of the materials having unidirectional raster θ = 0° and 90°. Furthermore, the result of the analysis by using a well-known Mohr’s circle confirmed the experimental tensile strengths and the failure mechanisms of the PLA material that had been printed with various raster orientations. Originality/value This study presented consistent results on the chemistry, physical, degree of crystallinity and mechanical properties of the FFF-processed PLA in responding to the increasing extruder temperature from 205°C to 225°C applied during the printing process. Unlike the results of the previous studies, all these properties were also found to be insensitive to the increase of extruder temperature. Also, the result of this research demonstrates the usability of Mohr’s circle in the analysis of stresses working on an FFF-processed PLA material in responding to the changes in raster orientation printed in this material.

Enhancement of the Compressive Strength of 3D-Printed Polylactic Acid(PLA) by Controlling Internal Pattern

Cost-efficient 3D-printing can create a lot of new opportunities in engineering as it enables rapid prototyping of models and functional parts. In the present study, Polylactic acid (PLA) cubic specimens with different types of infill patterns (IPs), rectilinear, grid and cuboid, were additively manufactured by Fused Filament Fabrication 3D-printing. The PLA cubes are fabricated with one perimeter and different IPs density (10, 20, and 30%). Subsequently, the compressive strengths of the PLA materials were measured in two loading directions, i.e., the layers building direction is parallel (PD) to the loading axis and perpendicular (ND) to the loading direction. An optical microscope was used to examine the deformed IPs in both loading directions. The compressive flow stress curves of the PLA cubes infilled with rectilinear and grid patterns exhibited strong fluctuations with lower compressive strengths in the loading direction along ND. The PLA with 30% grid IP revealed a superior strength of ~12 kN in the loading direction along PD. On the contrary, the same material exhibited a worst compressive strength 3 kN along ND.

Contact evolution in granular materials with inherently anisotropic fabric

This paper presents the results of two triaxial compression tests performed on approximately 9×103 oblate spheroids (lentils) with different initial orientations with respect to the loading axis (approximately 30° and 60°). Typical stress-strain information is complemented with x-ray tomography scans every 1 % strain. Starting from an initial labelling of particles, a new technique is used to obtain unprecedented detail of tracking of all the particles through time. This rich dataset is analysed from the perspective of inter-particle contacts (building on previous metrological work on this subject) revealing that the mean contact orientation in both samples rotates towards the direction of σ1 at a rate depending on the initial orientation. Different trends are observed for the alignment of contact orientation, with a significant evolution observed in the sample prepared at 30° which is not as pronounced as in the other sample.

Influence of unit cell parameters of tetrachiral mechanical metamaterial on its effective properties

In the paper, we study the mechanical behavior of a three-dimensional chiral mechanical metamaterial using numerical modeling. A feature of chiral structures is that during their uniaxial loading a twisting is observed along the loading axis. A rod of the mechanical metamaterial composed of 3 × 3 × 9 unit cells along the corresponding three orthogonal axes. The relative strain of uniaxial compression of the sample in the simulation did not exceed 3.3%. The simulation was performed by the finite element method in a threedimensional case. Original results on the dependencies of the rotation angle and the reaction of the rigidly fixed support of the metamaterial sample on the parameters characterizing the structure of the unit cell of the metamaterial are presented in this context. All the dependencies, except one, are nonlinear with portions of large and small changes.

Compressive Strength Parallel to the Grain in Relation to Moisture Content in Calamus simplicifolius Cane

This research aimed to investigate the compressive fracture behavior and the compressive strength parallel to the grain in relation to moisture contents (MC) below and above the fiber saturation point (FSP) in Calamus simplicifolius cane. FSP of the rattan was investigated using a dynamic vapor sorption (DVS) apparatus, and the fracture behaviors of compression parallel to grain were analyzed by three-dimensional X-ray microcomputed tomography. The study indicated that the value of FSP derived from the DVS method was 25 percent. The average compressive strength parallel to the grain was found to be 39 MPa at 3 percent MC, 30 MPa at 10 percent MC, 17 MPa at 12 percent MC, 12 MPa at 27 percent MC, and 10 MPa at 45 percent MC. The strains of the yield and densification stage were prolonged with increasing MC, whereas the stress in the linear elastic stage decreased with increasing MC. The cracks of the rattan core and the deflection angle at higher MC were larger than that of low MC. Below the FSP, the compressive failure of the rattan showed a shear band oriented around 45° to the loading axis, and the surface was rough. Above the FSP, the rattan samples showed brooming failure. The interface among fiber bundles was delaminated and the fiber surface in the failure area was smooth. The fracture toughness of the rattan was higher than that of wood, which suggests that the rattan might be more suitable for modeling and curved materials.

Micromechanical Modeling of Fatigue Crack Nucleation around Non-Metallic Inclusions in Martensitic High-Strength Steels

Martensitic high-strength steels are prone to exhibit premature fatigue failure due to fatigue crack nucleation at non-metallic inclusions and other microstructural defects. This study investigates the fatigue crack nucleation behavior of the martensitic steel SAE 4150 at different microstructural defects by means of micromechanical simulations. Inclusion statistics based on experimental data serve as a reference for the identification of failure-relevant inclusions and defects for the material of interest. A comprehensive numerical design of experiment was performed to systematically assess the influencing parameters of the microstructural defects with respect to their fatigue crack nucleation potential. In particular, the effects of defect type, inclusion–matrix interface configuration, defect size, defect shape and defect alignment to loading axis on fatigue damage behavior were studied and discussed in detail. To account for the evolution of residual stresses around inclusions due to previous heat treatments of the material, an elasto-plastic extension of the micromechanical model is proposed. The non-local Fatemi–Socie parameter was used in this study to quantify the fatigue crack nucleation potential. The numerical results of the study exhibit a loading level-dependent damage potential of the different inclusion–matrix configurations and a fundamental influence of the alignment of specific defect types to the loading axis. These results illustrate that the micromechanical model can quantitatively evaluate the different defects, which can make a valuable contribution to the comparison of different material grades in the future.

Evaluation of the Influence of the Location Solid-State Inclusions on the Amplitude-Frequency Characteristics under Pulsed Acoustic Excitation in the Process of Uniaxial Compression

Most dielectric materials and heterogeneous dielectric structures are operated under mechanical loads. Therefore, the usage of acoustic monitoring of the presence of defects and the destruction of such materials is difficult because of the high ultrasound damping decrement in these materials. This article presents assess the influence of the location of steel inclusions relative to the loading axis.

Computational analysis of tensile damage and failure of mineralized tissue assisted with experimental observations

In this study, deformation and failure mechanisms of mineralized tissue (bone) were investigated both experimentally and computationally by performing diametral compression tests on millimetric disk specimens and conducting finite element analysis in which a granular micromechanics-based nonlinear user-defined material model is implemented. The force–displacement relationship obtained in the simulation agreed well with the experimental results. The simulation was also able to capture location of the failure initiation observed in the experiment, which is inside out from the hole along the loading axis. Furthermore, propagation of micro-sized cracks into failure was observed both in the experiment using simultaneous slow-motion microscopy imaging and in the simulation analyzing the local distortion and local volume change within the specimen. The anisotropy evolution was found to be significant around the hole along the loading axis by evaluating the anisotropy index computed using finite element results. In conclusion, this work revealed that the prediction capability of granular micromechanics-based user-defined nonlinear material model (UMAT) is promising considering the match between the results and observations from the physical experiment and finite element analysis such as force–displacement relationship and failure initiation/pattern. This work has also shown that the tensile damage and failure of mineralized tissues can be characterized using diametral compression (split tension) test.