Search Results (5)

High-density polyethylene (HDPE) pipes are widely used for urban natural gas transportation. Pipes are usually welded using the technique of thermal butt fusion, which is prone to manufacturing defects that are detrimental to safe operation. This paper proposes a spatiotemporal singular value decomposition preprocessing improved total focusing method (STSVD-ITFM) imaging algorithm combined with ultrasonic phased array technology for non-destructive testing. That is, the ultrasonic real-value signal data are first processed using STSVD filtering, enhancing the spatiotemporal singular values corresponding to the defective signal components. The TFM algorithm is then improved by establishing a composite modification factor based on the directivity function and the corrected energy attenuation factor by adding angle variable. Finally, the filtered signal data are utilized for imaging. Experiments are conducted by examining specimen blocks of HDPE materials with through-hole defects. The results show the following: the STSVD-ITFM algorithm proposed in this paper can better suppress static clutter in the near-field region, and the average signal-to-noise ratios are all higher than the TFM algorithm. Moreover, the STSVD-ITFM algorithm has the smallest average error among all defect depth quantification results. Full article

This paper investigates the behavior of transverse defects under significant total strain in conditions of complex vortex metal flow implemented through the radial shear rolling (RSR) method. The aim of this study is to assess the applicability of RSR processing for the in-depth transformation of small ingots of special steel into bars, particularly for the manufacturing of structural elements in specialized construction projects such as nuclear power plants. Although a substantial total strain is anticipated to enhance the steel structure and contribute to defect closure, the question of the development or closure of potential casting defects remains unclear. To address this issue, model tests were conducted to simulate the implementation of RSR processing. Defect behavior data under very complex vortex metal flow and high strain conditions were obtained for the first time and have scientific merit. A small steel ingot with a 32 mm diameter, containing a simulated artificial defect in the form of a transverse through-hole with a 5 mm diameter, was employed. During rolling, the workpiece diameter was progressively reduced by 2 mm with each subsequent pass, reaching a final diameter of 20 mm. Additionally, to provide a more detailed visualization of the defect evolution process, the same defect was modeled in an aluminum bar over six passes, and changes in defect volume and shape were analyzed after each pass. A highly detailed 3D visualization of the actual defect evolution was achieved based on cross-sections from experimental workpieces. These data corresponded to the total strain levels obtained by finite element method (FEM) simulation. Notably, a consistent similarity was observed between the test results for both metals, revealing a reduction in defect volume of up to 67.7%. The deformational welding of defects in the outer sections, encompassing one-third of the rod’s radius, occurred in the initial passes. However, defects in the axial zone of the rods remained unclosed, lengthening and gradually decreasing proportionally to the elongation of the rod, akin to conventional rolling. Consequently, the radial shear rolling (RSR) method is unsuitable for ingots with substantial discontinuities in the axial zone post-casting. Nevertheless, the method ensures the total welding of defects located in the outer zones of the ingots, even with minor applied deformations and a slight decrease in the diameter of the deformed ingot. Such data were obtained for the first time and should contribute to future investigations in this field. Full article

Using experimental methods to study the influence of hole and cracks on the mechanical properties and fracture characteristics of rock-like mortar materials under biaxial compression conditions. The double crack specimens with hole depths from 0–100 mm are prefabricated to study the strength and deformation characteristics of the specimens under different lateral loads σ₂ = 0–6 MPa. The evolution process of secondary crack initiation, development, and connection of the hole-crack specimens are recorded. The results show that: (1) One type of rock mortar test material is prepared, and its main physical and mechanical parameters are all within the range of sandstone, which can effectively simulate the stress deformation characteristics of sandstone. (2) When the depth of the holes in cracked samples exceeds 50% of the length, the strength and deformation of the samples undergo a sudden change. When the depth of the hole in the crack specimen increases from 40 mm to 60 mm, the peak stress decreases most significantly. Moreover, the maximum values of the strain value at peak strength and lateral strain both occur at a hole depth of 60 mm. (3) When the cracked specimen contains through-holes, the failure mode is composite fracture and shear composite fracture. When the depth of the hole is different, the fracture forms include tension composite fracture, shear composite fracture, and composite fracture. Full article

Graphene with atomic thickness possesses excellent mechanical and electrical properties, which hold great potential for high performance pressure sensing. The exposed electron of graphene is always cross-sensitive to any pollution absorbed or desorbed on the surface, from which the long-term stability of the graphene pressure sensor suffers a lot. This is one of the main obstacles towards graphene commercial applications. In this paper, we utilized polymethylmethacrylate (PMMA)/graphene heterostructure to isolate graphene from the ambient environment and enhance its strength simultaneously. PMMA/graphene pressure sensors, with the finite-depth cavities and the through-hole cavities separately, were made for comparative study. The through-hole device obtained a comparable sensitivity per unit area to the state of the art of the bare graphene pressure sensor, since there were no leaking cracks or defects. Both the sensitivity and stability of the through-hole sensor are better than those of the sensor with 285-nm-deep cavities, which is due to the sealed gas effect in the pressure cavity. A modified piezoresistive model was derived by considering the pressure change of the sealed gas in the pressure cavity. The calculated result of the new model is consistent with the experimental results. Our findings point out a promising route for performance optimization of graphene pressure sensors. Full article

In the aerospace manufacturing industry, it is impossible to achieve precise and efficient automatic drilling and riveting for largescale composite board parts. The bottleneck is that the depth detection of rivet holes still relies on manual operation, which seriously affects the assembly efficiency and stability of composite board parts. In order to realize accurate and efficient on-machine automatic measurement for through holes in the automatic drilling and riveting process of largescale composite board parts, this paper presents a novel hole depth measuring device. Its mechanical structure is developed based on our newly designed measurement scheme and optical path, the purpose of which is to convert the hole depth data into displacement data of the probe motion. Its electrical hardware consists of three units: a laser transceiver unit to pick up laser spots; a displacement measuring unit to capture the probe movement in real time; and a driving unit to achieve motion control of the probe. Finally, the experimental results indicated that the proposed method and device are capable of performing automatic measurements for through-hole depth. In addition, factors affecting the measuring accuracy and stability of the device are initially analyzed and discussed, which lay a foundation for subsequent research on error compensation and probe calibration. Full article