Terms Of Mechanical Resistance Research Articles

Effect of water re-curing on the physico-mechanical and microstructural properties of self-compacting concrete reinforced with steel fibers after exposure to high temperatures

The present work aims to investigate the influence of water re-curing- on the physico-mechanical properties and the microstructural of heat-damaged steel fiber-reinforced self-compacting concrete. The experimental approach involves subjecting self-compacting concrete specimens, with and without steel fiber reinforcement, to various high temperatures (400, 600, and 800 °C), with a heating rate of 5 °C/minute. After cooling to ambient temperature, these samples were subjected to water re-curing for 30 days. Non-destructive measurement techniques, such as those of the ultrasonic pulse velocity and dynamic modulus of elasticity, and destructive measurement techniques, such as those of the flexural strength and compressive strength, were performed to assess the level of thermal damage caused to specimens as well as the degree of recovery. Moreover, scanning electron microscope (SEM) analyses were also performed to examine the morphological changes that occurred in concrete and at the fiber/concrete interface. The results obtained showed that the water re-curing process has remarkable effects on the recovery of the microstructure of thermally damaged specimens and its physical and mechanical properties as well. The recovery rate was more important for temperatures above 400 °C. Furthermore, it was found that self-compacting concretes reinforced with steel fibers recurred after exposure to 400 °C and 600 °C exhibited better behavior than self-compacting concrete without fibers, particularly in terms of mechanical resistance.

Modular sandwich panel system for non-loadbearing walls – Experimental mechanical, fire and acoustic testing

Investment in the construction industry has increased over the last years and conventional construction materials, techniques, solutions and practices cannot meet the current needs. Resources are not being used to their full potential and there is a lack of manpower. It is vital to evolve encouraging sustainable and quality cost-effective materials, techniques, solutions and practices, therefore also enhancing the construction workers’ quality of life. This work proposes a new modular sandwich panel system for interior walls partition applications. The modular sandwich panel is made of an extruded polystyrene boards (XPS) core and has three options as facesheets: gypsum plasterboard (PGC), fire resistant gypsum plasterboard (PGF) and magnesium oxide board (MGO). This is an alternative solution for partition walls based on five main factors: it has the potential to be reused; its modules are self-supported (they do not need vertical metal studs from floor to ceiling); it is easy to install (on-site) by only two people; it is quick to install; and it provides easy local access to the interior of sanitary facilities. This work also includes experimental research for evaluation of proposed the wall solution in terms of mechanical resistance and stability, fire safety and airborne sound insulation between adjacent rooms. Mechanical resistance testing includes impact resistance tests, simple compression load tests, sanitary appliance load tests and endurance cycle load tests. Fire resistance testing allows to assess the integrity and maintenance of the panel wall under fire conditions. Acoustic experiments aim to determine the weighted standardised sound level difference (DnT,w) between adjacent compartments separated by the proposed panel wall system. Mechanical resistance tests indicate that the panel wall system has acceptable mechanical performance, including the connections between the panel wall modules. Results indicate that fire resistance and sound insulation characteristics of the panel wall can be enhanced.

Sugarcane Bagasse as Aggregate in Composites for Building Blocks

Each year, hundreds of millions of tons of processed sugarcane generate, by weight, 25 to 30% of bagasse as waste, whose destination is combustion for energy cogeneration. This research proposes an alternative and more sustainable use for this waste. The use of sugarcane bagasse (SCB) as the single aggregate in composites for building blocks was studied. The raw bagasse was used without any treatment. As the binder, aerial lime and/or soil were used. Both provided enough mechanical strength for non-load-bearing walls. The composite of SCB with soil achieved the best performance in terms of mechanical resistance: 2.6 MPa in compressive strength and 2.1 MPa in bending strength, while the composite of SCB with lime achieved 1.76 MPa and 1.7 MPa, respectively. The higher number of fibers in the SCB/lime mixture provides better thermal insulation than clay brick or conventional concrete, such as “hempcrete”. The lime composites obtained greater water resistance and less loss of mechanical strength when saturated. However, the higher water absorption coefficient makes it necessary to apply a waterproof mortar on surfaces exposed to the weather. The replacement of supplied blocks by SCB blocks can offer a better and more economical solution that improves the quality of the built environment and is more ecofriendly.

Effect of Coating Thickness and Polyethylene Glycol’s Molecular Weight on Diltiazem Hydrochloride Release from Controlled Porosity Osmotic Pump Tablets

The purpose of this research was to design CPOP tablets to achieve controlled delivery of diltiazem hydrochloride (DH) up to 12 hours, which is a water-soluble calcium channel blocker with a short biological half-life. Two batches of osmotic tablet cores were prepared, containing DH with mannitol as an osmotic agent (1: 1.5 ratio). The tablet cores formulation with 10 mm diameter achieved the required technical and mechanical specifications. Direct compression technique was used to prepare the tablet cores which were evaluated in terms of mechanical resistance and uniformity of dosage units, followed by spray film coating using cellulose acetate as a former polymer of the semipermeable membrane and polyethylene glycol (PEG) as a pore forming agent. Several molecular weights of PEG (6000, 1500 and 400) were used and coating thickness levels were obtained. In vitro drug release, morphology of coating surface and the effect of pH change on release rate were investigated. Most of the prepared formulations demonstrated a burst release at the initial stage, which could be controlled by increasing the coating thickness. Formulations with PEG400 as a pore former presented better controlled and less burst release than those containing PEG6000, PEG1500, or a mixture of PEG6000: PEG400 (1: 1), and the pH change did not affect the drug release except in the initial stage.

RestArt method: innovative high-precision mechatronic-based procedure for fragmented stone statues restoration

Abstract The RestArt method is an innovative mechatronic-based procedure for high-precision reassembly of stone fragments intended to improve the restoration of ancient statues and architectural elements. The procedure comprises high-accuracy 3D laser scanning of two fragments positioned on the RestArt machine. After software simulated best-fitting of the two homologous fractured faces, the calculated roto-translation matrix is sent to the machine control system that moves one fragment to match the other one. The machine integrates a numeric-controlled moving drilling device for high-precision boring of the fractured surfaces at selected points for optimal rods insertion. This permits a very effective fixing of the fragments and allows multi-point fixing, which is practically impossible with conventional methods. Several stone specimens were experimentally recomposed through the RestArt and the traditional method. Then, they were compared in terms of mechanical resistance by shaking table tests, reproducing extreme strong-motion vibrations. The specimens recomposed through the RestArt method resulted less time-consuming and much more resistant to vibration excitation than the ones by traditional reassembly method. The RestArt method was applied to reassemble some original ancient statues currently exhibited at several Italian museums.

Resting hand splint model from topology optimization to be produced by additive manufacturing

PurposeThe purpose of this study is to validate a novel model of resting hand splint manufactured by additive manufacturing (AM) and compare it with the traditional model manufactured by high temperature thermoplastic in terms of cost, weight, volume and thermal comfort.Design/methodology/approachA novel resting hand splint model was created from the topology optimization (TO) and analyzed, by finite-element analysis, manufacturing cost and weight, with a traditional resting hand splint. A pilot clinical study was carried out to verify heat diffusion during the use of the two splints.FindingsThe results showed that compared with the traditional model, the novel model reduced the volume of material used by 35.48%, the weight of the orthosis by 17.56% and the maximum surface deformation by 171.17% when subjected to actuation forces. It was also verified that, when manufactured with Nylon by AM, the new model is 1.5 times cheaper than the traditional model made of Polypropylene. The result of the thermographic analysis showed greater temperature variation in the use of the traditional splint (+4.6°C) compared to the temperature variation observed in the nylon splint (2.1°C).Practical implicationsThese results have as clinical relevance the demonstration of the feasibility of manufacturing functional orthoses that are more comfortable, cheaper and lighter than traditional ones.Originality/valueThis study describes the use of TO to manufacture a novel resting hand splint, which was compared with the commonly used traditional splint in terms of mechanical resistance, weight, cost and thermal comfort.

Mechanical Performance of Chairside Ceramic CAD/CAM Restorations and Zirconia Abutments with Different Internal Implant Connections: In Vitro Study and Finite Element Analysis.

(computer-aided design-computer-aided manufacturing) CAD/CAM monolithic restorations connected to zirconia abutments manufactured with a chairside workflow are becoming a more common restorative option. However, their mechanical performance is still uncertain. The aim of this study was to evaluate the mechanical behavior of a combination of a zirconia abutment and monolithic all-ceramic zirconia and lithium disilicate crown manufactured with a chairside workflow, connected to titanium implants with two types of internal connection—tube in tube connection and conical connection with platform switching. They were thermally cycled from 5 °C to 55 °C and were subjected to a static and fatigue test following ISO 14801. The fractured specimens from the fatigue test were examined by SEM (scanning electron microscopy). Simulations of the stress distribution over the different parts of the restorative complex during the mechanical tests were evaluated by means of (finite element analysis) FEA. The mechanical performance of the zirconia abutment with an internal conical connection was higher than that of the tube in tube connection. Additionally, the use of disilicate or zirconia all-ceramic chairside CAD/CAM monolithic restorations has similar results in terms of mechanical fracture and fatigue resistance. Stress distribution affects the implant/restoration complex depending on the connection design. Zirconia abutments and monolithic restorations seem to be highly reliable in terms of mechanical resistance.

Chitosan-Coated Poly(lactic acid) Nanofibres Loaded with Essential Oils for Wound Healing.

Chronic skin wounds are characterised by a non-healing process that makes necessary the application of wound dressings on the damaged area to promote and facilitate the recovery of skin’s physiological integrity. The aim of the present work is to develop a bioactive dressing that, once applied on the injured tissue, would exert antibacterial activity and promote adhesion and proliferation of fibroblasts. Nanofibres consisting of poly(lactic acid) (PLA) and essential oils (EOs) were electrospun and coated with a medium molecular weight chitosan (CS). Black pepper essential oil (BP-EO) or limonene (L), well-known for their antibacterial properties, were added to the PLA/acetone solution before electrospinning; phase separation phenomena occurred due to the poor solubility of the EOs in the PLA solution and led to fibres having surface nano-pores. The porous electrospun fibres were coated with CS to produce hydrophilic membranes that were easy to handle, biocompatible, and suited to promote cellular proliferation. The fibrous scaffolds were tested in terms of mechanical resistance, wettability, antibacterial activity, in-vitro cytotoxicity, and ability to promote fibroblasts’ adhesion and proliferation. The results obtained proved that the CS coating improved the hydrophilicity of the fibrous mats, enhanced EO’s antibacterial potential, and promoted cell adhesion and proliferation.

Role of Diisocyanate Structure on Self‐Healing and Anticorrosion Properties of Waterborne Polyurethane Coatings

AbstractOrganic coatings are extensively investigated as possible solution to prevent or at least retard the occurring of corrosion processes on metal surfaces. Their actual breakthrough is still hampered by the risk of barrier properties loss because of local failure of the coating integrity. To address this issue, self‐healing coatings, which are intrinsically able to recover from damages upon exposure to external stimuli, are currently gaining increasing attention. Herein, waterborne polyurethanes (PU) are synthesized, and a Diels–Alder adduct is added into the polymeric backbone to endow the material with self‐healing functionality. The effect of different diisocyanate in PU synthesis is explored, namely isophorone diisocyanate, 4,4′‐dicyclohexylmethane diisocyanate (HMDI), and hexamethylene diisocyanate. The obtained results highlight the key role of the interactions among soft and hard segments in ultimately defining the coating performances. Actually, the combination of Fourier transform infrared spectroscopy, atomic force microscopy and X‐ray diffration analysis reveals that the HMDI‐based PU have showed the best balance in terms of H‐bonding strength among hard segments and crystallinity degree in the soft ones. This allows to reach a good compromise in terms of mechanical resistance, anticorrosion properties, and self‐healing ability.

Suitability Assessment of PLA Bottles for High-Pressure Processing of Apple Juice.

The aim of the present study is to assess the use of polylactic acid (PLA) bottles as an alternative to polyethylene terephthalate (PET) ones for high-pressure processing (HPP) of apple juice. The treatment of PLA bottles at 600 MPa for 3 min did not cause alterations in the packaging shape and content, confirming the suitability of PLA bottles to withstand HPP conditions as well as PET bottles. Quantification of total mesophilic bacterial and fungal load suggested HPP treatment can be effectively applied as an alternative to pasteurization for apple juice packed in PLA bottles since it guarantees microbial stability during at least 28 days of refrigerated storage. The headspace gas level did not change significantly during 28 days of refrigerated storage, irrespective of the bottle material. Color parameters (L*, a*, and b*) of the HPP-treated juice were similar to those of the fresh juice. Irrespective of the packaging type, the total color variation significantly changed during storage, showing an exponential increase in the first 14 days, followed by a steady state until the end of observations. Overall, PLA bottles proved to offer comparable performances to PET both in terms of mechanical resistance and quality maintenance.

Enzyme-Functionalized Cellulose Beads as a Promising Antimicrobial Material.

The extensive use of antibiotics over the last decades is responsible for the emergence of multidrug-resistant (MDR) microorganisms that are challenging health care systems worldwide. The use of alternative antimicrobial materials could mitigate the selection of new MDR strains by reducing antibiotic overuse. This paper describes the design of enzyme-based antimicrobial cellulose beads containing a covalently coupled glucose oxidase from Aspergillus niger (GOx) able to release antimicrobial concentrations of hydrogen peroxide (H2O2) (≈ 1.8 mM). The material preparation was optimized to obtain the best performance in terms of mechanical resistance, shelf life, and H2O2 production. As a proof of concept, agar inhibition halo assays (Kirby-Bauer test) against model pathogens were performed. The two most relevant factors affecting the bead functionalization process were the degree of oxidation and the pH used for the enzyme binding process. Slightly acidic conditions during the functionalization process (pH 6) showed the best results for the GOx/cellulose system. The functionalized beads inhibited the growth of all the microorganisms assayed, confirming the release of sufficient antimicrobial levels of H2O2. The maximum inhibition efficiency was exhibited toward Pseudomonas aeruginosa (P. aeruginosa) and Escherichia coli (E. coli), although significant inhibitory effects toward methicillin-resistant Staphylococcus aureus (MRSA) and S. aureus were also observed. These enzyme-functionalized cellulose beads represent an inexpensive, sustainable, and biocompatible antimicrobial material with potential use in many applications, including the manufacturing of biomedical products and additives for food preservation.

Evaluation of the Mechanical Parameters of Ultrasonically Welded Textile Composite Structures for Protective Footwear

Textile materials are used in protective footwear due to their good mechanical and hygienic properties and to provide thermal insulation. This work presents a technological process of designing ultrasonically welded composite structures characterised by various densities of welding spots. The study involved three variants of composite structures made of three layers. The composite structures developed were tested in terms of mechanical properties and were statistically analysed in terms of the effects of welding spot density and reinforcing nonwoven thickness on the protective parameters. Inserts made of ultrasonically spot-welded textile composite structures may offer protective footwear users greater comfort in terms of mechanical resistance. The evaluation method proposed may be a useful tool in assessing textile composite structure inserts for protective footwear.

3D Printing with the Commercial UV-Curable Standard Blend Resin: Optimized Process Parameters towards the Fabrication of Tiny Functional Parts.

Stereolithography 3D printing is today recognized as an effective rapid prototyping technique in the field of polymeric materials, which represents both the strengths and the weaknesses of this technique. The strengths relate to their easy handling and the low energy required for processing, which allow for the production of structures down to the sub-micrometric scale. The weaknesses are a result of the relatively poor mechanical properties. Unfortunately, the choice of the right material is not sufficient, as the printing parameters also play a crucial role. For this reason, it is important to deepen and clarify the effect of different printing conditions on final product characteristics. In this paper, the behavior of commercial Standard Blend (ST Blend) acrylic resin printed with stereolithography (SL) apparatus is reported, investigating the influence of printing parameters on both the tensile properties of the printed parts and the build accuracy. Twenty-four samples were printed under different printing conditions, then dimensional analyses and tensile tests were performed. It was possible to find out the optimum printing setup to obtain the best result in terms of mechanical resistance and printing accuracy for this kind of resin. Finally, a micrometric spring was printed under the optimal conditions to demonstrate the possibility of printing accurate and tiny parts with the commercial and inexpensive STBlend resin.

Effective tool for assessment of the quality of barrier creams - relationships between rheological, textural and sensory properties

The efficiency of barier creams (BC) in the prevention of occupational skin diseases is closely related to their mechanical, rheological but also sensory properties. The measurement procedure we elaborated, which simulates the spreadability conditions on the skin and evaluation whether the structure reconstruction occurs (hysteresis loop test, shear rate dependence of normal force), allows the assessment of the effectivness of the BC in terms of mechanical resistance and its adhesion to the skin surface. In this thesis an effort was made to define the impact of the human factor – the product application on skin – on the efficiency of medical devices for cutaneous use. Creams‘ performance such as the spreadability or the feeling on the skin during and after application, which mostly determine users willingness to use them systematically and rigorously, have been linked to parameters obtained during the structure analysis and to rheological properties. Moreover an attempt has been made to correlate the values of basic textural properties with rheological parameters determined by viscoelasticity and classic flow analysis. Instrumental analysis of selected BC products demonstrated a good correlation with organoleptic tests carried out on probands. The applicability of our tool for quality evaluation of BC has been confirmed.

Concrete Formulation Study for Informal and Semi-Informal Construction Sectors

The present work consisted in carrying out a study on the effective formulation of concrete for an optimal resistance to compression (fc28) between 20 and 30 MPa for the sites animated by the actors of the informal and semi-informal sectors of the construction. Studies have been carried out on projects under construction, by taking samples of fresh concrete in order to evaluate their real compressive strengths. These surveys show that there is a problem in the concrete formulation, as nearly 2/3 of the results show the lack of technical knowledge on concrete formulation practices. Indeed, on eight sites surveyed and whose fresh concrete samples were taken, only two sites (7 and 8) report fairly consistent results. Their 28-day compressive strength values are respectively 35.36 and 22.18 MPa. In addition, various formulations proposed with aggregates from different quarries or extracts from the bed of the Congo River, were determined in the laboratory. This study allowed us to obtain fairly objective results overall, which is characteristic of concretes of required quality. Of the six (06) formulation proposals, average resistances of 19.6 MPa at 07 days and 25.28 MPa at 28 days were obtained. These results at 28 days are in the range of 20 to 30 MPa, set as objective in this study. These formulations can be a reliable source for concrete manufacturers in these construction sectors. Similarly, the statistical study based on principal component factor analysis tests has shown that the most appropriate formulation, in terms of mechanical resistance, is that proposed with sand extracted from the Congo River (formulation 3). This is justified by the fact that this sand is consistent and has a good granular distribution.

Experimental investigation of the mechanical behaviour of soft carbonate rock/grout interfaces for the design of offshore wind turbines

Since a few years, in France, the development and construction of offshore wind farms in different sites of the country is investigated. The wind turbines will be installed in soft carbonate rock formations (calcarenite, limestone), the mechanical properties of which can vary in a significant way according to the location of the site. Once installed, the bored piles will be sealed with grout in the hosting rock. It is well known that the mechanical behaviour of piles is mainly governed by the behaviour of the interface at the contact between the structure and the hosting rock. The study of the mechanical behaviour of these interfaces, being the weakest points in terms of mechanical resistance, is of great importance for the improvement of the design methods of such infrastructures. The shear response of the rock/grout interface is studied with laboratory experiments in the 3SR lab (Grenoble). The interface's mechanical properties are characterised by a series of shear tests under Constant Normal Stiffness (CNS), these conditions being the most representative of the in-situ conditions. Interface samples of a roughness representative of the in-situ drilling traces, are tested under different levels of applied normal stiffness. The shear response is studied for both monotonic and cyclic shear paths, while all tests are performed under wet conditions. The failure mechanisms are explored, taking into account the contrasting mechanical properties of the two materials composing the interface, as well as, the evolution of the geometrical profile of the interface. The correlation between roughness and the mechanical response of the interface is investigated and the importance of an existing roughness is discussed.

The influence of process parameters on mechanical properties and corrosion behavior of friction stir welded aluminum joints

Aim of the present paper is to analyze if and how the process parameters (namely rotational speed S and feed rate f) affect both the mechanical properties and the corrosion behavior of friction stir welded (FSWed) butt joints made of AA7075 and AA2024 alloys and their combination. Tensile tests were performed orthogonally to the welding direction on specimens having the welding nugget placed in the middle of gage length. Rockwell tests were carried out on each specimen moving from the joint axis until the hardness of the base material was reached. A clear dependence of the Ultimate Tensile Strength (UTS) from the process parameters were observed when the joints are obtained using the same material while the effect is not so evident when two different materials are concerned. In almost all cases, the best conditions, in terms of mechanical resistance, were obtained for intermediate values of rotational speed and feed rate. Further tests were performed for evaluating the corrosion behavior and the stress corrosion cracking susceptibility of FSWed joints. In particular, local corrosion potential measurements were executed and longtime immersion tests were carried on four points bending specimens loaded up to 80% of the Yield Strength (TYS), in 35 g/L sodium chloride solution. The same tests were replicated on unloaded specimens. The potential trends are always well defined and much higher for the AA2024 alloy, since it is more noble than the AA7075 alloy. Mixed welding allows to identify the AA7075 alloy as an anode part, having a lower copper concentration and a high concentration of zinc. A correlation of some corrosion behaviors to the mechanical characteristics was evidenced, in particular for the AA2024 alloy.

Grain size and loading conditions influence on fatigue crack propagation in a Cu-Zn-Al shape memory alloy

Due to their capability to recover the initial shape, Shape Memory Alloys (SMAs) are widely used in many applications. Different grades are commercially available and they can be classified considering either their chemical compositions (e.g., Cu based, Ni based, Fe based) or according to their mechanical behaviour. The most used SMAs are the Ni based alloys thanks to their performances both in terms of mechanical resistance and in terms of fatigue resistance, but their costs are quite high. Cu based alloys are good competitors of the Ni based alloys. The recent optimization of their chemical composition improved both the corrosion resistance in aggressive environments and their mechanical performances. In this work, the influence of the grain size on fatigue crack propagation in two Cu-Zn-Al SMAs has been investigated focusing on the damage micromechanisms.

Grain size influence on fatigue behaviour in a CuZnAl PE SMA

Due to their capability to recover the initial shape, Shape Memory Alloys (SMAs) are widely used in many applications. Different grades are commercially available and they can be classified considering either their chemical compositions (Cu based, Ni based, Fe based and so on..) or according to their mechanical behaviour. The most used SMAs are the Ni based alloys thanks to their performances both in terms of mechanical resistance and in terms of fatigue resistance, but their costs are quite high. Cu based alloys are good competitors of the Ni based alloys. The recent optimization of their chemical composition improved both the corrosion resistance in aggressive environments and their mechanical performances. In this work, the influence of the grain size on fatigue crack propagation in two Cu-Zn-Al SMAs focusing on the damaging micromechanisms.

Innovative, Translucent and Multi-functional Components for the Building Envelope: technological and performance optimization

The paper describes the actions aimed at the technology and performance optimization of an innovative, multi-functional building component made of precast and pre-stressed glass blocks useful for the construction of sustainable building envelopes able to reduce the energy consumption and to produce clean energy from the sun. The design optimization of different sub-components and the choice of the right materials for guaranteeing their good response in terms of mechanical resistance, thermal and acoustic insulation, light transmission, electricity production, integration with other components, dimensional coordination, are particularly described.