1,721,018 research outputs found
Hemp as eco-friendly substitute of glass fibres for gypsum reinforcement: Impact and flexural behaviour
No full textGypsum board walls and ceilings are nowadays widely used in the buildings, due to a number of outstanding advantages, such as lightness, fire resistance, sound insulation, economy, durability and ease of installation. The above constructive elements have no structural function, however in case of collapse or damage they constitute a danger for the safety of people and an economic loss in terms of restoration costs, downtime and damage to the assets contained in the building.
Therefore, more and more often, gypsum panels with an enhanced toughness and strength are requested, to offer greater resistance to the impact loads, to vandalism and from seismic events. For this purpose, glass fibre reinforced gypsum (GFRG) is widely used. However, considering the current environmental awareness and the increasing interest in the use of eco-friendly materials, in this paper the effectiveness of bio-degummed hemp fibres, as substitutes of glass fibres, has been highlighted. Both static and dynamic mechanical tests demonstrated that the use of hemp fibres lead to gypsum-based composites with features comparable with those of GFRG
A numerical approach to optimize the toolpath strategy for polymers forming
No full textIncremental sheet forming is a relatively new technology with a deformation strategy that resembles the layered manufacturing principle of rapid prototyping; thanks to this, it can represent a viable way to form metal and polymer sheets, guaranteeing high customization and cost-effectiveness. On the other hand, and particularly when considering thermoplastic sheets, the components obtained by this process suffer from peculiar defects like, for example, twisting and wrinkling. A way of reducing the risk of such defects is to optimize the toolpath strategy to lower in-plane forming forces. To pursue this aim, the present work follows a numerical approach; a commercial FE code was used to simulate the incremental forming of polycarbonate sheets by varying the toolpath strategy. The investigation of some features like the forming forces and the deformation states was carried out, with the goal of determining an optimized toolpath strategy for the reduction of the incremental forming forces and the consequent expectation of reduced risk of failures and defects for incremental formed polymer sheets
Punch Tool based Out-of-Plane Shear Behaviour of GFRP Composites
No full textIn this experimental work, the behaviour of unidirectional glass fibre-epoxy composites under a cutting force was studied, in order to better understand the cutting mechanisms of processes involving but not limited to composite materials.
Starting from composite panels manufactured by resin infusion process, dedicated specimens were obtained and subjected to a quasi-static punch-shear test. Eight different fibre orientation angles with respect to the direction of the cutting force were considered.
For each case, different stress-strain behaviours were observed and discussed. The differences were also investigated, in terms of damage propagation, by means of microscopic observations of the cutting zone
One-shot drilling process for thin CFRP/Aluminium alloys stacks
No full textThe aerospace industry pursues lighter, stronger, and more fuel-efficient aircraft, relying on lightweight
materials. This study investigates one-shot drilling of thin hybrid stacks, including carbon fiber-reinforced
polymer (CFRP, 2.2 mm thick), and aluminum alloys (Al2024-T3, 1.6 mm thick, and Al7075-T6, 1.0 mm
thick), crucial in modern aircraft structures. The challenge of thin materials lies in their reduced flexural
stiffness, which significantly impacts the quality of the final hole and the effects of the process parameters
on torque and thrust force. The experimental approach involves drilling each material separately to
analyze thrust force, torque, and hole quality, then comparing outcomes with one-shot drilling in thin
hybrid stacks. The results highlight that thin hybrid stacks are challenging to drill because their reduced
flexural stiffness significantly impacts the final hole quality and the effects of the process parameters on
torque and thrust force differently from what typically occurs for the drilling of conventional hybrid
stacks
Effects of toolpath on defect phenomena in the incremental forming of thin polycarbonate sheets
No full textIncremental sheet forming has been largely investigated in the last two decades because of its versatility and cost-effectiveness, which make it viable for manufacturing highly customized parts as well as small- and medium-sized batches. This process allows for reaching greater formability compared to conventional sheet-forming processes. In contrast, it is affected by defects like twisting, which strongly influence the geometric accuracy of the formed parts. These aspects are dramatically accentuated when forming soft materials like thermoplastics. With these premises, the following research aims to investigate the effects of the toolpath strategy on the occurrence of failures and defects in the incremental sheet forming under
very severe process conditions. Cone frusta with a fixed wall angle were obtained by thin polycarbonate sheets, imposing four unidirectional helical trajectory-based toolpaths, one traditional, and three stair strategies. The analysis of the forming forces, the evaluation of the worked surfaces, and the monitoring of the defectiveness highlight the advantages of a stair toolpath strategy in terms of reduced twisting and loading and high surface quality, regardless of the lubrication conditions
Numerical and theoretical approach to evaluate the clamping force and the interlayer gap extent during drilling of stacked materials
No full textIn the aeronautical industry, one-shot drilling of stacked materials is a widely adopted and established solution. However, ongoing discussions persist, particularly regarding the issue of interlayer gap formation that arises when two or more unsealed materials are drilled together. This study aims to present a simplified and reproducible theoretical model based on the equation of the elastic curve applied to structural schemes that discretize and describe the interlayer gap phenomenon in the drilling process. The model is designed to estimate the extent of the interlayer gap phenomenon and predict the clamping force required for its reduction when an end-effector is employed as a clamping device during the drilling of stacked sheets. Experimental and finite element analyses were conducted to validate the results of the proposed theoretical model. Each model was developed and applied to a real structural unit of a fuselage panel, considering actual boundary conditions in terms of structural constraints and geometric features of the assembly. The results obtained in this study demonstrate that the proposed one-dimensional theoretical model consistently aligns with experimental and numerical observations obtained through finite element analysis. This offers an effective and readily implementable solution in an industrial context as a tool for sizing the clamping force exerted by a clamping device
Lightweight hemp/bio-epoxy grid structure manufactured by a new continuous process
No full textThis paper investigates the mechanical properties in terms of tensile, flexural, compression, and Charpy impact strength of a new lightweight grid structure in bio-composite material based on woven hemp fabric and bio-epoxy resin. The main intent was the manufacturing of bio-composite with high specific mechanical properties produced through a new process that can be easily implemented in industrial production, and that can produce low density composites in a continuous way with a good level of repeatability. This was done by using two hemp fabric types, that mainly differ in the fabric mesh size. Several hemp/bio-epoxy resin grid structures with different density (in the range of 0.47–0.80 g/cm3) and thickness (in the range of 4.3–12.3 mm) were obtained and their properties were widely investigated. The results showed interesting mechanical properties possessed by the bio-composites so manufactured, highlighting their possible use as core for sandwich composite structures
Dynamic-Mechanical Behaviour of Bio-composites
No full textPLA-hemp bio-composites with different reinforcement content were manufactured by compression moulding process. Both flexural and impact properties were investigated and compared to the unreinforced polymer. In addition, also the creep behaviour adopting the Arrhenius theory was determined, in order to better understand the industrial application limits of PLA reinforced by natural fibres. For this purpose, DMA tests were carried out, in order to evaluate the activation energy and to apply the Time-Temperature Superposition model to the compliance curves obtained by short-time creep tests
The Influence of Thermal Oxidation and Tool-Sheet Contact Conditions on the Formability and the Surface Quality of Incrementally Formed Grade 1 Titanium Thin Sheets
No full textThe incremental sheet metal forming process combines a series of characteristics, such as the capacity to produce large deformations, flexibility and low-cost tooling, making it preferable to conventional forming processes. One of the key factors in this process are the contact conditions between the forming tool and the sheet to be formed. The incremental forming process of titanium and its alloys is widely studied; on the other hand, the influence of some heat treatments that can induce superficial modifications is not fully known and understood yet. In this study, the influence of thermal oxidation and tool-sheet contact conditions on the formability and the surface quality of grade 1 titanium thin sheets manufactured by incremental forming was investigated by using both a sphere and a hemispherical head tool. The results of the experimental campaign, based on the production of conical and pyramid frusta, highlight the beneficial effects of the heat treatment on the process repeatability, reducing the occurrence of galling for all the contact conditions, and provide information on the quality of the worked surfaces
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