Papers by Keyword: Cracking

Abstract: In the cosmetics packaging industry, UV coating is applied to enhance surface characteristics by providing scratch resistance, a glossy finish, stain resistance, and improved durability against environmental exposure. UV coating is a curing process that utilizes ultraviolet (UV) lamp radiation. This process is influenced by several parameters, including conveyor speed, UV lamp temperature, and the distance between the UV lamp and the product. However, in the current packaging process, these parameters are often set based on routine practices rather than standardized guidelines. As a result, improper UV curing can lead to cracking defects that appear after the product assembly stage. These cracks are caused by suboptimal UV exposure during the curing process, which compromises the mechanical integrity of the product. This paper intends to determine the appropriate standard temperature settings based on a comparative analysis of UV lamp temperatures and distances. Experiments were conducted using four UV lamps with temperature settings of 50°C, 75°C, and 100°C, repeated across five trials. The results show improved mechanical properties and a significant reduction in cracking defects. Furthermore, the findings support the development of more efficient and standardized settings for the UV curing process.

Abstract: This paper investigates the influence of two proprietary redispersible polymers, i.e. Ethylene Vinyl Acetate (EVA) and Styrene Acrylate (SA) - at varying contents of 10%, 15% and 20% by mass of cement - on cracking and crack-determining material properties in non-structural concrete patch repair mortars. Five mortar mixes, one control mix and four polymer-modified mixes, were designed, developed and tested under a controlled laboratory environment. The effects of polymer type and content on macroporosity, the age at cracking and crack widths in restrained shrinkage specimens, compressive strength, direct tensile strength, elastic modulus, drying shrinkage and tensile relaxation were investigated. From the test results, it was observed that polymer type and content influence cracking and crack-determining material properties significantly. An increase in polymer content resulted in a significant reduction in elastic modulus, crack widths, compressive and direct tensile strength. An increase in polymer content also resulted in a significant increase in drying shrinkage, tensile relaxation and the age at cracking. The performance of EVA polymers, with respect to the susceptibility to cracking, was better than that of SA polymers at constant polymer content. Overall, the addition of polymers improved the cracking performance of the non-structural concrete patch repair mortars under investigation significantly, highlighting their potential for use in practice to improve the durability of non-structural concrete patch repairs.

Abstract: High strength 7xxx series aluminium alloys are widely utilized in the aerospace, automotive and other manufacturing industries due to their low cost, high specific strength, high stiffness strength and fracture toughness. Additive manufacturing presents new opportunities in producing 7xxx series aluminium alloys such as reduced material waste, shorter lead time, and increased design freedom. This paper reviews the current progress in Wire Arc Additive Manufacturing (WAAM) of 7xxx series aluminium alloys, a technology that offers benefits such as better energy absorption than alternative laser-based processes, high deposition rates, and unrestricted build size. A classification of the AM processes utilized to fabricate aluminium alloys and WAAM process variants for fabricating aluminium alloys are introduced. Also, some common defects including porosity, solidification cracking and volatile elements loss encountered during the WAAM process of 7xxx series aluminium alloys are discussed. Whilst porosity remains a major issue in 7xxx series aluminium alloys produced via WAAM, several opportunities to minimize or eliminate the defects through process selection and alloy development are presented.

Abstract: The article deals with the analysis of the development of hydration heat in massive concrete structures and focuses mainly on risk factors which could lead to the appearance of early age cracking in the structure shortly after concreting. As part of the analysis, a parametric study was carried out, which was focused not only on the size of cracks on the surface of the structure, but also on the evaluation of the temperature gradient, where the ratio of the temperature difference and the distance between two points was investigated. During the study, different variants of the type and length of surface covering and different boundary conditions in terms of ambient temperature during individual seasons were considered. The numerical analysis was performed using nonlinear numerical calculations in ATENA software. At the conclusion, an evaluation of the effect of different types of covering of the concrete structure on the reduction of the number and size of surface cracks caused by hydration heat is carried out.

Abstract: This paper presents a case study of solar drying of hydroxide sludge in the region of Marrakesh, Morocco. The experiments of solar greenhouse drying processes of the hydroxide sludge were studied in summer and winter seasons. The representative samples were in three volumes. The greenhouse sludge dryer was designed and constructed as a horticultural plant. Results showed that the dry of the three samples was reached in only 13 hours in summer and 25 hours in winter. The time of solar greenhouse drying registered was significantly lower compared to several studies. The higher values of drying rate were obtained in early hours of experiments in summer. The maximum ranges obtained were 0.25 kg water/kgDS.h for the hot season and 0.020 kg water/kgDS.h for the cold season. The important influence of the temperature had a greater effect with wind speed on drying rate. The sludge water evaporation caused a large volume reduction with a shrinkage during the processes in both seasons.

Abstract: Plastic industry development has increased the amount of plastic waste, including LDPE plastic film, therefore LDPE waste processing becomes essential, such as thermal or catalytic cracking. Cracking is the breakdown of complex hydrocarbons into simple and commercial hydrocarbons (C₃-C₄₀). The catalytic cracking is preferred due to lower temperatures, which is 200-300°C instead of 500-700°C. In this study, catalyst selection, acid impregnation of catalyst, catalyst loading (wt%), N₂-gas-purging, feed-to-solvent weight-ratio, temperature, and reaction time were studied to determine the most suitable process condition to obtain the highest liquid fraction. In this study, the catalytic cracking was conducted at 20 bar with kerosene as solvent, with and without N₂-gas-purging at several temperatures (265 and 295°C), solvent-to-feed weight-ratios (5:1 and 4:1), catalyst types (bentonite, SiO₂ and ZSM-5), catalyst loading (wt%) (1.0wt%; 5.0wt%; 7.0wt%; 9.0wt%; 10.0wt%), and reaction time (1-3 hours). The best results were with N₂-gas-purging using 10.0wt%-bentonite in (5:1) solvent-to-feed weight-ratio for 1 hour at 295^οC produced 54.9wt% of liquid fraction and without N₂-gas-purging at 265°C produced 54.5wt% of liquid fraction, indicating the possibility of N₂-gas-purging exclusion in future studies. Additionally, this study has promoted bentonite as a potentially viable catalyst for LDPE plastic waste catalytic cracking.

Abstract: This research aims to analyze the mechanical behavior of concrete reinforced with polyolefin fibers. The intention is to evaluate the possibility of using concrete as a structural material without steel bars in its interior. For this purpose, specimens with different dosages of polyolefin fibers were prepared, and bending and compression tests were carried out. The results show no significant increase in mechanical strengths, especially in bending, but it is interesting in the mechanical behavior after the first cracking. Controlling cracking is considered beneficial for sustainability.

Abstract: Pores and weak bonding are the inherently drawbacks for thermally sprayed coating. Laser beam is an attractive approach to remelt thermal spray coating for obtaining fully dense coating with metallurgical bonding with substrate. However, defects of holes or cracks are highly inevitable with unmatching remelting processing parameters. In this work, a thermally sprayed Cr₃C₂-NiCr cermet coating by high velocity oxygen fuel spraying was post-processed by laser remelting with a series of varying beam energy densities from 37.5 J/mm² to 225 J/mm². The defect evolution was investigated by both experimental and numerical simulation methods. Large holes and through-thickness cracks were typical defects observed in the remelt coating by optical microscopy. The experimental results show that remelting-induced defects evolve into three stages with laser energy density. The effect of energy density on remelt structure was further verified with the temperature field by numerical simulation with ABAQUS code. The stress field interpreted the crack formation at periodical formation sites. The results on the defect evolution shed light on obtaining functional coatings for industrial applications.

Abstract: Fabric Reinforced Cementitious Matrix (FRCM) materials are increasingly common for strengthening existing masonry structures. Their popularity is due to their many advantages with respect to resin-based composites, especially when applied to stone supports. The constitutive behaviour of FRCM materials is defined by the combination of their tensile response and the bond behaviour with the masonry support, both depending on complex stress transfer mechanisms between matrix and fabric, especially in the post-cracking stage. This paper presents a numerical study which aims to predict the mechanical behaviour of FRCM systems through simple 2D models of truss elements and non-linear springs to simulate the fabric-to-matrix and composite-to-substrate interaction. The comparisons between results of numerical approach and experimental responses showing that the proposed methodology is an effective and easy tool to predict the mechanical behaviour of FRCM composites.

Abstract: Throughout time, the use of lignocellulosic resources has been implemented in the development of building materials. Among these resources, natural fibers are used as mineral binders reinforcement due to their specific mechanical properties. This experimental investigation focused on effect of flax and hemp fiber reinforcement on the resistance of pozzolanic-based mortars to cracking due to restrained plastic shrinkage. Results were compared with polypropylene fiber reinforcement and with control mortar without fibers. The quantity of fibers added to the mortar mix were respectively 0.25% - 0.5% by mass of binder for polypropylene fibers and 0.5% - 1% by mass of binder for flax and hemp fibers. All fibers have a similar length of 12 mm. The cracking sensitivity was evaluated based on two different methods: the first consists in casting the mortar in a metal mold with stress risers whose criteria are inspired by the ASTM standards. The second consists in pouring the mortar on a brick support. In order to assess the effect of fibers on cracking due to restrained plastic shrinkage, the number of cracks, total crack area and maximum crack width within the first 6 hours after casting were determined using digital image correlation (DIC). Results showed that the flax and hemp fibers were more effective in controlling restrained plastic shrinkage cracking compared to polypropylene fibers. With a natural fiber of 1% by mass of binder, maximum crack width was reduced by at least 70% relative to control mortar based specimens. Natural fibers show great ability to propensity for cracking due to restrained plastic shrinkage; so that, they could be an alternative and ecological solution for polypropylene fibers.