Extended CT Void Analysis in FDM Additive Manufacturing Components

Additive manufacturing (AM) is the term for a number of processes for joining materials to build physical components from a digital 3D model. AM has multiple advantages over other construction techniques, such as freeform, customization, and waste reduction. However, AM components have been evaluated by destructive and non-destructive testing and have shown mechanical issues, such as reduced resistance, anisotropy and voids. The build direction affects the mechanical properties of the built part, including voids of different characteristics. The aim of this work is an extended analysis of void shape by means of X-ray computed tomography (CT) applied to fused deposition modeling (FDM) samples. Furthermore, a relation between the tensile mechanical properties and digital void measurements is established. The results of this work demonstrate that void characteristics such as quantity, size, sphericity and compactness show no obvious variations between the samples. However, the angle between the main void axis and the mechanical load axis α shows a relation for FDM components: when its mean value μ(α) is around 80 (degrees) the yield strength and Young’s modulus are reduced. These results lead to the formulation of a novel criterion that predicts the mechanical behavior of AM components.

Biaxial testing of metal samples on testing machines with one load axis

The necessity of experimental studies to assess the growth rate of fatigue cracks under biaxial loading is substantiated. An overview of testing machines for biaxial testing of metal samples, devices and fixtures used to ensure biaxial loading is made. An original device for distributing the vertical force of the testing machine along two axes of a cruciform sample is described

Effect of Fiber Direction and Stress Ratio on Fatigue Property in Carbon Fiber Reinforced Epoxy Composites

The fatigue limit and crack growth behavior of slit specimens of carbon fiber reinforced epoxy composites were investigated. The fatigue limit was defined by the maximum stress amplitude that the specimen endured 106 times repeated stress when S-N curve was used. The highest fatigue limit was obtained when all the fiber directions were parallel to the load axis. The fatigue limits were evaluated in the cases of composites using alternately parallel and perpendicular to the load axis and compared with the result of the specimen having all the carbon fiber orientations were parallel to the load axis. When the measured value of the fatigue limit was lower, shear damage to the epoxy resin and peeling of fiber from epoxy resin occurred clearly. According to those results, it was expected that the fatigue limit of smooth specimens of carbon composites with long fibers can be evaluated from the results of the slit specimens.

Calcaneal Tendon Collagen Fiber Morphometry and Aging

Fibrillar collagen in tendons and its natural development in rabbits are discussed in this paper. Achilles tendons from newborn (~7 days) to elderly (~38 months) rabbits were monitored in intact (ntendons=24) and microtome sectioned (ntendons=11) states with label-free second harmonic generation microscopy. After sectioning, the collagen fiber pattern was irregular for the younger animals and remained oriented parallel to the load axis of the tendon for the older animals. In contrast, the collagen fiber pattern in the intact samples followed the load axis for all the age groups. However, there was a significant difference in the tendon crimp pattern appearance between the age groups. The crimp amplitude (A) and wavelength (Λ) started at very low values (A=2.0±0.6 µm, Λ=19±4 µm) for the newborn animals. Both parameters increased for the sexually mature animals (>5 months old). When the animals were fully mature the amplitude decreased but the wavelength kept increasing. The results revealed that the microtome sectioning artifacts depend on the age of animals and that the collagen crimp pattern reflects the physical growth and development.

An anisotropic, viscoplastic power law for face-centred cubic crystals: comparative evaluations in the Goss and Brass orientations of channel die compression

An anisotropic, viscoplastic power law is introduced and applied to analysis of the Goss and Brass orientations, and compared with predictions from rate-independent theory and experiment. The structure of the new power law is so chosen that it has the capability of approaching rate-independent results for lattice rotation and crystal shearing, after finite rotation about the load axis, in the range of unstable lattice orientations in (110) channel die compression. (Rate-independent predictions of shear and lattice rotation are in good to very good agreement with experiments on aluminium and copper in that range, whereas classic isotropic power-law results are not.) It is established that, for sufficiently large power-law exponent n , the new anisotropic, elasto-viscoplastic theory predicts: (i) lattice stability in each of the Goss and Brass orientations, consistent with both experiment and rate-independent theory; (ii) zero crystal shear in the Goss orientation, also consistent with both; (iii) finite shear in the Brass orientation, in very good agreement with experiment and rate-independent theory; and (iv) a lateral-constraint stress that remains essentially elastic in both orientations, as predicted by rate-independent theory and close to experimental measurements for aluminium and copper in the Brass orientation.

Fragmentation, Texturing and Plastic Flow in the Subsurface of Friction-Processed Copper Single Crystal

Copper single crystals grown according to the Bridgman method and having their axes [] or [11 aligned with the normal load axis were processed by dry sliding. As shown, sliding-induced severe plastic deformation occurred in the subsurface of single crystals and caused formation of a lip by mechanism of texture formation. The SEM structure of this lip was found to be composed of fragments with their shapes dependent on the single crystal orientation with respect to normal load and friction force.

A Kind of Spatial Angular Magnetic Gear Transmission

Gear exciting is of vital importance in modern power transmission systems. But when the requirements of angular gear transmission are needed, the shortcomings of the current mechanical and magnetic gear transmission are even more obvious. The traditional mechanical gear boxes have the construction of direct mechanical contact, whose disadvantages are low efficiency, noisy, apt to lubricate, easy to produce vibrations to be damaged and so on. And the existing magnetic gear is coaxial which can’t meet the need of angular transmission. In this paper, the construction of a kind of spatial angular magnetic gear, which has no direct mechanical contact between the driven axis and load axis, is proposed. Besides, the principle of the gear ratio is introduced and a concrete magnetic gear is analyzed. The results show that the range of the angle of this magnetic gear can be very large.

Numerical Analysis of Exfoliation Corroded Holed Aluminum Plates Repaired with Adhesively Bonded Composite Patches

A 3D FE model of exfoliation corroded holed aluminum plates repaired with adhesively bonded composite patches was established in this paper, and then the stress distribution in the repaired aluminum plate was analyzed. The result shows after repairing in the exfoliation corroded holed aluminum plate gets reduced for 33.62%, and the repaired aluminum plates undergoes bending deformations due to the offset between load axis and centroidal axis of the repaired structure.

Effects of deviatoric stresses in the diamond-anvil pressure cell on single-crystal samples

The nonhydrostatic stress states that are developed in the pressure media within diamond-anvil pressure cells have been investigated by single-crystal X-ray diffraction. Measurements of unit-cell parameters of small single crystals under nonhydrostatic conditions are used to calculate the deviatoric strains and, through knowledge of the elastic tensors of the crystals, the stress state of the media. The results confirm that the stress state is effectively cylindrically symmetrical with the stress parallel to the load axis being greater than the radial stresses. The stress state in a given medium can be predicted and can be used to design a specific response of the lattice parameters of small single crystals to pressure beyond the hydrostatic pressure limit of the pressure medium.

The Effect of Cold Work on the Creep Properties of Copper

Spent nuclear fuel is in Sweden planned to be disposed of by encapsulating in waste packages consisting of a cast iron insert surrounded by a copper canister. The waste package is heavy. Throughout the manufacturing process from the extrusion/pierce-and-draw manufacturing to the final placement in the repository, the copper is subjected to handling which could introduce cold work in the material. It is well known that the creep properties of engineering materials at higher temperatures are affected by cold working.The study includes creep testing of four series of cold worked, oxygen-free, phosphorus doped copper (Cu-OFP) at 75 °C. The results are compared to reference series for as-received material carried out in a recent study. Two series of copper cold worked in tension (12 and 24 %) and two series cold worked in compression (12 % parallel to creep load axis and 15 % perpendicular to creep load axis) were tested.The results show that pre-straining in tension of copper leads to prolonged creep life at 75 °C. The creep rate and ductility are reduced. The influence on the creep properties increases with the amount of cold work. Cold work in compression applied along the creep load axis has no effect on the creep life or the creep rate. Nonetheless the ductility is still impaired. However, cold work in compression applied perpendicular to the creep load direction has a positive effect on the creep life. Cold work in both tension and compression results in a pronounced reduction of the initial strain on loading. Yet the high value of the area reduction, 90 %, is unaffected by the degree of cold work.