Effect of Fungus, Aspergillus sp. F1-1, on the Corrosion Behavior of PCB-HASL in Humid Atmospheric Environment

Fungi, as one of the serious factors causing microbiologically influenced corrosion (MIC), can shorten the service life of electronic materials which are wildly used in the atmospheric environment. In this study, the effect of Aspergillus sp. F1-1 (A. F1-1) isolated from PCB samples after the exposure test in Xishuang Banna on the corrosion behavior of PCB-HASL was investigated. The presence of the A. F1-1 posed a threat of local corrosion on PCB-HASLs. An obvious decrease of pH was observed in PCB with A. F1-1 due to the various organic acids secreted by A. F1-1. The presence of the fungi also led to serious surface cracking and delamination. Creep corrosion and micro-hole corrosion were accelerated in the presence of A. F1-1 compared to the control. Additionally, the metabolic activities of A. F1-1 were associated with enrichment of Cu-containing corrosion products under the hypha.

Image-Based Automated Width Measurement of Surface Cracking

The detection of cracks is an important monitoring task in civil engineering infrastructure devoted to ensuring durability, structural safety, and integrity. It has been traditionally performed by visual inspection, and the measurement of crack width has been manually obtained with a crack-width comparator gauge (CWCG). Unfortunately, this technique is time-consuming, suffers from subjective judgement, and is error-prone due to the difficulty of ensuring a correct spatial measurement as the CWCG may not be correctly positioned in accordance with the crack orientation. Although algorithms for automatic crack detection have been developed, most of them have specifically focused on solving the segmentation problem through Deep Learning techniques failing to address the underlying problem: crack width evaluation, which is critical for the assessment of civil structures. This paper proposes a novel automated method for surface cracking width measurement based on digital image processing techniques. Our proposal consists of three stages: anisotropic smoothing, segmentation, and stabilized central points by k-means adjustment and allows the characterization of both crack width and curvature-related orientation. The method is validated by assessing the surface cracking of fiber-reinforced earthen construction materials. The preliminary results show that the proposal is robust, efficient, and highly accurate at estimating crack width in digital images. The method effectively discards false cracks and detects real ones as small as 0.15 mm width regardless of the lighting conditions.

P137 DEGRADATION RESISTANCE OF PVDF MESH IN VIVO IN COMPARISON TO PP MESH

Aim To researched the degradation resistance of PVDF mesh by comparing its morphological and chemical condition with PP mesh. Material and Methods PVDF and PP meshes analysed in this study were received from a previous animal experiment. To expose the surface of explanted meshes, a tissue removing method with protease was used and the result of this cleaning process was tested by X-ray Photoelectron Spectroscopy (XPS). The morphological condition of the mesh surface was compared using Scanning Electron Microscopy (SEM) and the chemical condition concerning degradation was analysed through Fourier Transform Infrared Spectroscopy (FTIR). The surface condition of PVDF mesh after 3-, 6-, 12- and 24-month implantation was illustrated and compared with two types of PP meshes. Results XPS revealed an absence of nitrogen, confirming the successful removal of tissue residues using protease. SEM results presented no notable morphological surface change of the PVDF mesh and progressive surface cracking processes over time of both types of PP meshes. FTIR spectra of the implanted PVDF meshes had no considerable difference from the spectrum of the pristine mesh, while FTIR spectra of both types of PP meshes had extra chemical functional groups increasing with implantation time, indicating progressive degradation. Conclusions PVDF mesh does not show signs of degradation up to 24 months after implantation while PP meshes progressively degrade with increasing time under the same conditions, which appears as worsening Environmental Stress Cracks. This study highlights the morphological and chemical stability of the PVDF mesh and demonstrates that the PVDF mesh is more resistant to degradation in comparison to the PP meshes.

Influence of the Deep Cryogenic Treatment on AISI 52100 and AISI D3 Steel’s Corrosion Resistance

The effect of deep cryogenic treatment (DCT) on corrosion resistance of steels AISI 52100 and AISI D3 is investigated and compared with conventional heat-treated counterparts. DCT’s influence on microstructural changes is subsequently correlated to the corrosion resistance. DCT is confirmed to reduce the formation of corrosion products on steels’ surface, retard the corrosion products development and propagation. DCT reduces surface cracking, which is considered to be related to modified residual stress state of the material. DCT’s influence on each steel results from the altered microstructure and alloying element concentration that depends on steel matrix and type. This study presents DCT as an effective method for corrosion resistance alteration of steels.

Surface Cracking and Fractal Characteristics of Bending Fractured Polypropylene Fiber-Reinforced Geopolymer Mortar

Fiber is effective in restricting cracks and improving the toughness of geopolymer composites, but few studies have focused on the surface crack characteristics of fiber-reinforced geopolymer composites. In this paper, after flexural tests of polypropylene fiber-reinforced geopolymer mortar, the surface cracking image was collected by a digital camera and cracking information was extract by deep learning. Finally, the cracking and fractal characteristics were specifically discussed. The semantic segmentation network can accurately extract surface cracks for calculating various parameters. The results showed that the mean intersection over union (mIoU) and mean pixel accuracy (mPA) of the cracks are 0.8451 and 0.9213, respectively. Generally, the crack length, width, area, and fractal dimension of the specimen are all increased with the increase in the fiber volume fraction. These crack parameters grow rapidly when the fiber content is small, and the growth of the crack parameters gradually slows down as the fiber volume fraction increases to approximately 1.5%. The highest crack parameter values were found in the geopolymer mortar, with a 0.48 water–binder ratio and 12 mm fiber length. The variation of the bottom crack length and the side crack fractal dimension can be used to represent the overall crack variation patterns. Meanwhile, the crack parameters increase with the increased fiber factor in a quadratic function. Based on these crack parameters, the critical fiber factor and dense fiber factor of polypropylene fiber-reinforced geopolymer mortar were 200 and 550, respectively. They are greater than those of fiber-reinforced Portland cementitious composites. The influence of various crack parameters on the flexural strength is in the order of the crack area, width, length, and fractal dimension.

The Influences of Sand Content and Particle Size on the Desiccation Cracks of Compacted Expansive Soil

The desiccation cracks in expansive soil, which are a common natural phenomenon, have a significant negative impact on the engineering properties of the soil and are the direct cause of many engineering problems and geological disasters. This study aims to investigate the influences of sand content and particle size on desiccation cracks of the compacted expansive soil. First, samples of compacted expansive soil with five sand contents and four sand size groups were prepared. Then, a series of drying tests were performed. The dynamic variation of geometric parameters of the surface crack network during evaporation was quantitatively analyzed by using digital image processing technology and fractal theory. The results demonstrated that the increase of the surface-cracking areas in the early and later stages was manifested by the increase of the crack length and crack width, respectively. In the same size of sand particle group (0.15, 0.3 mm), as the sand content (dry weight ratio of soil sample) increased from 0% to 40%, the surface-cracking ratio (the ratio of the crack area to the total surface area of the soil sample) showed a decreasing trend (13.20%, 11.42%, 10.50%, 8.98%, and 7.71%, respectively). When the sand content (40%) was the same, as the sand size groups increased from [0.15 mm, 0.3 mm) to [1.18 mm, 2.36 mm), the surface-cracking ratio also presented a decreasing trend (7.71%, 7.69%, 4.35%, and 3.73%, respectively). The changing law of the fractal dimension of cracks was the same as that of the surface crack ratio. During the drying process, the deformation of the sample was characterized by centripetal shrinkage or cracking, which were mainly affected by the boundary conditions of the sample. This research’s results verify the effectiveness of sand to improve the dry-shrinkage characteristics of expansive soil, providing a reference for the improvement of roadbeds and the treatment of soil slopes in expansive soil areas.

Thermal Analysis of Disc Brake System

Brakes are one of the most significant safety systems in an automobile. In the braking process, the rotor will be exposed to large stresses which result in surface cracking, overheating of brake fluid, seals and other components. Therefore one of the main tasks of the braking system is to reduce the surface temperature of the brake rotor. This can be achieved by choosing the right material which will undergo the least thermal stresses. In this project, thermal analysis for vented disc brake rotor of Mahindra Bolero’s done, for providing an efficient material for disc brake rotor and brake pads which can dissipate heat generated during braking at faster rate and also being structurally safe. Keywords: Braking system, Disc Brake Rotor, Thermal, Structural Analysis, CATIA V5, ANSYS WORKBENCH

Transient Thermal Analysis of Disk Brake System under Varying Velocities and Pad Material Properties

The Enormous progressions in the field of automobiles have led their car engines to have enriched brake power in vehicles. The braking system’s efficiency should be at par with the engine to decelerate the car from a given speed within a less braking distance. The disc rotor and brake pads design and material while counting other impacting factors contribute to braking efficiency. The disc rotor will be exposed to large stresses which result in surface cracking, overheating of brake fluid, seals and other components. Many factors are affecting it as coefficient of friction between brake pad and disk rotor surface, thermal conductivity of pad material. Hence to reduce thermal stresses we can choose right pad material. In this project, thermal analysis for vented disc brake rotor of Mahindra Bolero’s done, for providing an efficient material for disc brake rotor and brake pads with 0 to 12 % of steel powder as filler materials are used which can dissipate heat generated during braking at faster rate and also being structurally safe Keywords: Braking system, Disc Brake Rotor, Thermal, Structural Analysis, CATIA V5, ANSYS WORKBENCH, Pad Material properties