Additionally, industry pressure has added more superalloy powders to the available processing including AM108. It is not only the Print operation and orientation that provides a change in material properties, it is also the required post processing via Hot Isostatic Pressure (HIP) Heat Treat and shot peen that change mechanical properties to a level of noticeable difference in comparison to equiaxed cast or wrought materials. Based on research done at the Tokyo Metropolitan University, it is shown that creep rupture and ductility are typically lower for additive printed Ni based superalloys compared to wrought or cast material. The directionality of print is a major influencing factor along with grain size. Additionally, wear properties are typically better as seen with the studies done on additive Inconel 718 due to surface condition; the study also demonstrated the laser power's influence on density and microstructure. Material Density that is generated during the laser processing parameters can further influence crack behavior such that crack reopening post HIP process is reduced when density is increased. It is critical to have a full overview of the material along with its processing from print to required post-print to be able to finalize the mechanical properties for design use.
For the reasons above, the mechanical properties of alloys produced by SLM can deviate substantially from those conventionally manufactured counterparts in their as-built state. A central characteristic of SLM-manufactured alloys is large anisotropy in mechanical properties . While the grain structure in cast metals is typically characterized by roughly uniform, isotropic grains, alloys manufactured using SLM exhibit substantial elongation of grains in the build direction. The anisotropy in grain structure is associated with anisotropy in the distribution of defects, the direction of crack propagation, and ultimately the mechanical properties.
For thin structures, using shell (3D, 2D axisymmetry) and plate (2D) elements can be very efficient. The formulations allow for the transverse shear deformations needed to model thick shells. You can prescribe an offset in the direction normal to a selected surface, which simplifies modeling where you work with a full 3D representation of the geometry. The results from shell element analyses can be presented as a full solid representation.
Due to the complex process of the insulation layer patch in solid rocket motor (SRM), only manual patch could be used. Sometimes weak bonding or debonding in each joint surface was inevitable. This study is aimed at determining the crack group effect of insulation and interfacial debonded crack in the wide-temperature SRM. The crack group appeared in the front area of the ahead stress-release boot and was induced by low temperature, axial overload, or interface bonding failure. Based on the viscoelastic finite element method, singular crack elements and singular interfacial crack elements at the tips of crack group were established to calculate -integral. Varying according to the length and position of cracks, the -integral of crack tips was, respectively, calculated to prejudge their stability and the crack group effect. The results showed that collinear crack group appeared in the front stress-release boot layer, and the crack group had a certain shielding effect on the main crack when the SRM was launched at low temperature. When noncollinear crack group appeared in the front stress-release boot layer, the crack group effect changed with the length of the main crack. The crack group first had a shielding effect on the main crack and then had a strong strengthening effect. The experimental test of the simulated specimen revealed that numerical simulation results matched the experimental test results.
Typically, researchers use special elements to describe the particularity of the crack tip region [13, 14]. According to Equations (1) and (2), the first derivative of displacement at the crack tip obtains the stress , whose first derivative has singularity. To approximate displacement and stress at the crack tip to the real field, it is necessary to construct a singular element with displacement behavior so that the stress of the first derivative has singularity behavior.
The division of three-dimensional interface crack finite elements and the construction method of the -integral cylinder enclosure are shown in Figure 2. The interface singular crack element is used to describe the interface crack tip whereas other parts without cracks are described by ordinary elements. The solution of the three-dimensional -integral value of each crack and interface crack is mainly divided into two steps : one is to calculate the two-dimensional -integral of the end crack as shown in Figure 2(a) and the plane () is perpendicular to the line in front of the crack (the intersection is node ).
The second step is to integrate the two-dimensional -integral point by point along the front line of the crack to obtain the three-dimensional -integral. In the structural finite element division, a closed cylindrical enclosure is constructed to surround the singular crack elements along the front line of the crack, as shown in Figure 2(a). The and are the outer surfaces and inner surfaces of the cylindrical enclosure, respectively. On the other hand, and are divided into two end faces of the cylindrical enclosure surface whereas is the two crack surfaces of the cracked body. For the interface crack, integrate the two-dimensional -integral point by point along the front line of the interface crack to obtain the three-dimensional -integral along the front line of the interface crack as shown in Figure 2(b). A closed cylindrical enclosure surface is formed to surround the front line of the interface crack. The two end surfaces of the cylindrical enclosure surface are and , the outer surface , the inner surface , and the upper and lower interface crack surface .
The surfaces , , , , and S5 together form the volume domain V. The surface integral can be transformed into volume integral by Gauss theorem [4, 10]. is the strain energy, and is the normal direction outside the surface. The unit vector of interface crack propagation direction was whereas is the volume weight function, the modulus of on the outer surface is 0, on the inner surface , and changes smoothly between two values in the surface. is the surface tension on end faces , , and interface crack surface . The -integral of each node along the line before the interface crack can be expressed as follows:
6000 series aluminum grades contain 0.2-1.8% silicon and 0.35-1.5% magnesium as the major alloying elements. These grades can be solution heat-treated to increase their yield strength. The precipitation of magnesium-silicide during aging hardens the alloy. A high silicon content enhances precipitation hardening, which can result in reduced ductility. Still, this effect may be reversed by the addition of chromium and manganese, which depresses recrystallization during heat treatment. These grades are challenging to weld because of their sensitivity to solidification cracking, and proper welding techniques must be employed.
Cast aluminum is produced by a casting process. This process involves pouring molten aluminum, together with specific amounts of the alloying elements, into a mold to form the desired shape of the alloy. Cast aluminum alloys generally have lower tensile strength than wrought aluminum. They are susceptible to cracking and shrinkage. However, they are more cost-effective. These alloys can be formed into a wide variety of shapes because molten aluminum can flexibly take the shape of the mold cavities. 076b4e4f54