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Formation of Weld and Deposited Metal
Published in German Deyev, Dmitriy Deyev, Surface Phenomena in Fusion Welding Processes, 2005
Undercuts have a substantial influence on welded joint’s strength. Being planar defects, they induce a considerable stress concentration and noticeably lower the static and, particularly, dynamic strength of a welded joint for the most diverse materials. Fatigue strength of butt-welded joints with undercuts depends on the depth of the undercut, magnitude of tensile residual stresses, and type of the joint.1 Influence of the undercut depth and level of tensile residual stresses for butt-welded joints’s is shown in Figure 5.8. As is seen, the fatigue life of a welded joint decreases with increase of undercut depth. However, the greater the thickness of the metal being welded, the greater is the admissible depth of the undercuts. Therefore, it is more correct to evaluate the influence of undercut depth on the fatigue strength of the welded joint by the ratio of admissible size of undercut d to sheet thickness δ, as is proposed.319 According to the data of Iida, Sato, and Nagai’s, welded joint fatigue strength decreases by 5% at d/δ = 0.01, by 10% at d/δ = 0.01 and by 15% at d/δ = 0.02.319 In this case, similar to lacks-of-penetration, the adverse influence of undercuts is enhanced, if they are in the zone of high tensile residual stresses. It is established318 that the fatigue strength of welded joints with undercuts depends little on the mechanical properties of the steel used as the base metal (Figure 5.9).
Development and challenges in finite element modelling of post-installed anchors in concrete
Published in Structure and Infrastructure Engineering, 2023
Chandani Chandra Neupane, Jessey Lee, Tilak Pokharel, Hing-Ho Tsang, Emad Gad
Among the different types of post-installed anchors, adhesive anchors were most commonly studied. Screw anchors and undercut anchors were the least studied. It was observed that studies done using Hilti Corporation FEA software (Li et al., 2005, 2013; Nienstedt & Dietrich, 1995; Nienstedt & Mattner, 2001) focused more on working principle and had limited information on FE modelling and analysis. This may be because the focus on those studies were for their product development. However, it is difficult for researchers to replicate, validate or investigate anchorage behaviour utilising those FE models due to absence of adequate information such as modelling considerations and constitutive models, material properties and validation. Since MASA (Ozbolt et al., 2001) was developed at the University of Stuttgart and they are the pioneer in anchorage studies, it was observed that numerical studies using MASA were generally carried out for research conducted at the University of Stuttgart. In recent research (Bokor et al., 2018, 2019a; Bokor & Sharma, 2021) using MASA, Femap software developed by Siemens was used for pre and post processing for model development and evaluation of results. Besides the above two software, all others commonly used software (ABAQUS, ATENA, LS-DYNA, ANSYS) are commercial software.
MEMS enabled suspended silicon waveguide platform for long-wave infrared modulation applications
Published in International Journal of Optomechatronics, 2022
Xinmiao Liu, Qifeng Qiao, Bowei Dong, Weixin Liu, Cheng Xu, Siyu Xu, Guangya Zhou
For the receiving substrate, an SOI wafer (5 µm thick Si device layer and 2 µm thick BOX layer) is also manually diced into a 1 × 1 cm chip for fabrication. Unlike the photonic device layer which uses EBL for lithography and DRIE for etching due to high dimensional accuracy requirement, the receiver substrate directly uses the optical lithography (Laserwriting) process to define the large cavity pattern with photoresist (AZ1512). Since the Si layer on the receiver substrate is much thicker, the Bosch process is adopted for high aspect ratio plasma etching. The scallop sidewall will not affect the device's performance here. After removing the photoresist, the chip is put into DHF for 10 min for BOX removal without too much undercut. A metal deposition and lift-off process are executed together with a photonic device chip to make the bottom electrode inside the cavity area on the bottom substrate. Once the photonic device chip and receiving chip are ready, the manual membrane transfer process can be carried out.
Investigations on the fabrication of a patterned tool by chemical etching
Published in Materials and Manufacturing Processes, 2021
Tanmay Tiwari, Akshay Dvivedi, Pradeep Kumar
The width (Wf) and depth (d) of the form, as shown in Fig. 4 were taken as the response characteristics. A stereo-zoom microscope (Model: SMZ-745 T; Manufacturer: NIKON) was used to measure the width of the form produced on the workpiece. Sectioned view (Fig. 4) of the feature was observed under the microscope for measuring the depth. The average values of width and depth were obtained by measuring at the different locations along the length of the form. Experiments were conducted thrice, and an average value of responses viz. width (Wf) and depth (d) were considered. Table 2 gives the average values of response characteristics. Figure 3 shows the etching scheme as it starts vertically and then proceeds simultaneously in vertical and horizontal directions, resulting in an undercut. Undercut (Fig. 4) results in etching of geometric feature in the horizontal direction, which provides an obtained width of feature lesser than that of the mask. In the present work, the objective is to obtain deep features as well as features having less undercut, i.e., width (dimensional value) close to that of mask width (dimensional value).