Mechanical properties and energy–absorption capabilities of thermoplastic sheet gyroid structures

The development of additive manufacturing and lattice structures has created opportunities for the development of lightweight impact–absorption structures that can overcome most constraints of previously used materials such as expanded polystyrene foams. However, for the successful application of such structures, the effects of their variables in their mechanical performance must be established. In this study, the mechanical properties and energy absorption of thermoplastic sheet gyroid structures were investigated and compared with the performance of current materials. Consequently, the specimens were tested after changing the main variables, i.e., cell size and volume fraction, of various thermoplastic materials such as acrylonitrile butadiene styrene, polylactic acid, thermoplastic polyurethane, and polyamide 12. Finally, they were tested in a quasi-static compression test and their deformation stages were photographed. The stress–strain curves of all materials changed after adopting the sheet gyroid structure, exhibiting three distinct regions: linear elastic, long collapse plateau, and densification that made them particularly applicable for energy absorption. Volume fraction affected the layer collapse. The elastic geometrical stiffness increased for higher volume fractions and smaller cells. In addition, the peak and plateau stresses increased at higher volume fractions, and while smaller cells were not directly affected. Additionally, the area under the curves increase with the volume fraction; hence, for most materials, specific energy absorption was larger for higher volume fractions. The constituent material properties contributed significantly to the structural behavior, exhibiting three primary deformation mechanisms, i.e., elastomeric, elastic–plastic, and elastic–brittle, resulting in a wide spectrum of properties for each application requirement. The comparison of the optimal properties with the expanded polystyrene demonstrated the ability of sheet gyroid structures to overcome most of its challenges, exhibiting a superior specific energy absorption, ability to withstand various impacts, letting air flow in its all axes, and being recyclable. Thus, sheet gyroid structures can be considered promising alternatives

A study on interlaminar behavior of carbon/epoxy laminated curved beams by use of acoustic emission

The interlaminar tensile strength of carbon/epoxy laminated curved beams with variable thickness and through-the-thickness tufted reinforcement is studied experimentally by means of a four-point-bending test in accordance with ASTM D6415. These tests are monitored by the acoustic emission (AE) technique in order to gain deeper knowledge of the delamination onset and post-failure behavior. The results show that AE technique has proven to perform well when identifying delamination onset and its evolution after failure. In addition to this, AE has demonstrated to be an appropriate tool to assess the manufacturing quality of the carbon/epoxy laminated curved-beam, once the right pattern has previously been established

Analysis of the capability of cork and cork agglomerates to absorb multiple compressive quasi-static loading cycles

Despite the higher specific mechanical properties and the lower density of polymeric foams, these materials present cumulative damage behaviour that implies in the second and successive impacts, their mechanical properties decrease drastically. However, cork and cork agglomerates have the ability to absorb multiple impacts so they could be a more suitable material in some products, such as bumpers and helmets. This article is focused on the study of five different cork agglomerates and a natural cork under four different maximum deformations subjected to four consecutive compression loading cycles. Main diagrams, such as the stress–strain, energy density and efficiency, and the variation in diverse parameters, such as the absorbed energy density and maximum efficiency, were investigated and compared with an expanded polystyrene foam

Characterization of cork and cork agglomerates under compressive loads by means of energy absorption diagrams

Cork and cork agglomerates could be suitable replacements for petroleum-based polymeric foams due to their similar internal structure of cells and grains. Additionally, cork products have a renewable origin and are recyclable. Despite these notable properties, few studies have analysed the mechanical properties, especially the specific properties, of these materials under compressive loads. Moreover, although efficiency, ideality, and energy-normalized stress diagrams are commonly used for polymeric foams and 3D-printed lattice structures, these types of diagrams are not yet applied to cork products. It must be highlighted that efficiency diagrams are plotted only against nonspecific properties so, this article proposes additionally the use of nonspecific properties to compare materials not only in terms of properties per unit volume instead but also in terms of properties per unit mass that is more suitable for certain applications in which the weight is crucial. The materials studied herein include three different white cork agglomerates, a brown cork agglomerate, a black cork agglomerate, natural cork, and expanded polystyrene foam, which are subjected to quasi-static compressive loads

Numerical simulations of gyroid structures under compressive loads

Numerical simulations are essential for predicting the mechanical properties of different structures like gyroids that center this study. Three different methods are explored: shell elements, solid elements, and homogenization. Results reveal that homogenization is only suitable for obtaining the properties in the elastic zone, whereas solid models can determine also the behaviors in the plateau zone and the densification point. In the case of shell elements model, it can predict the elastic behavior model and the levels of stress in the plateau zone but with a lower accuracy than the solid element, but it cannot predict the densification point

Mechanical properties of diamond lattice structures based on main parameters and strain rate

The diamond triply periodic minimal surface structure has a high mechanical property–weight ratio. They can be modified by changing their internal parameters or the material. They are generated using the additive manufacturing (AM) that possibilities the use of various materials for generating zones with different mechanical properties or by modifying their internal parameters. However, the effects of internal parameters in the mechanical properties have not been defined in detail. Furthermore, the strain rate modifies these mechanical properties. In this study, the effects of the internal parameters and strain rate were evaluated and additionally, the failure mechanism of the structures

Development of a fatigue life prediction methodology for welded steel semi-trailer components based on a new criterion

This paper presents a procedure developed to predict the fatigue life in components made of steel, based on the mechanical properties of the base material and Thermally Affected Zones (TAZs) owing to welding. The fatigue life cycles of the studied components are obtained based on a certain survival probability provided by a Weibull distribution. This procedure is thought to be applied on semi-trailer components, and therefore it is proposed for the steels that are typically used in its manufacturing. A criterion for the adjustment of the exponent and the stress stroke of the fatigue life curve in welded joints is proposed in which the parameters that define the alternating stress versus the number of cycles to failure (S-N) curve are obtained exclusively from the ratio between the base material yield stress of a given steel and the strength of its Thermally Affected Zone. This procedure is especially useful for steels that do not have a complete characterization of their fatigue parameters. These developments are implemented in a subroutine that can be applied in commercial codes based on Finite Element Method (FEM) to obtain a fatigue life prediction. Finally, a numerical-experimental validation of the developed procedure is carried out by means of a semi-trailer axle bracing support fatigue analysis

Mechanisms of Airborne Infection via Evaporating and Sedimenting Droplets Produced by Speaking

For estimating the infection risk from virus-containing airborne droplets, it is crucial to consider the interplay of all relevant physical-chemical effects that affect droplet evaporation and sedimentation times. For droplet radii in the range 70 nm < R < 60 μm, evaporation can be described in the stagnant-flow approximation and is diffusion-limited. Analytical equations are presented for the droplet evaporation rate, the time-dependent droplet size, and the sedimentation time, including evaporation cooling and solute osmotic-pressure effects. Evaporation makes the time for initially large droplets to sediment much longer and thus significantly increases the viral air load. Using recent estimates for SARS-CoV-2 concentrations in sputum and droplet production rates while speaking, a single infected person that constantly speaks without a mouth cover produces a total steady-state air load of more than 104 virions at a given time. In a midsize closed room, this leads to a viral inhalation frequency of at least 2.5 per minute. Low relative humidity, as encountered in airliners and inside buildings in the winter, accelerates evaporation and thus keeps initially larger droplets suspended in air. Typical air-exchange rates decrease the viral air load from droplets with an initial radius larger than 20 μm only moderately

Desarrollo de un nuevo sistema de material compuesto: resistente al fuego y altamente estructural

Infrastructure and rail sectors share two singularities in terms of materials: highly structural performance and strict fire requirements. Moreover, there is a common growing interest in both sectors: the use of organic matrix composite materials due to their high performance, lightweight and in-service behavior. Traditionally, fire fillers have been added to the matrix, decreasing its mechanical performance in a critical way. A study about composite materials formed by three different matrices and four different carbon fibers will be presented in this paper. A number of laminates have been manufactured by using these composite materials in order to analyze both the resin processing and the compatibility of the different matrices and fibers. This study is a need due to the fact that these matrices are fire-related and therefore further problems may arise in comparison with standard matrices.Los sectores de la construcción y del ferrocarril tienen dos aspectos en común en el ámbito de los materiales: la utilización de materiales altamente estructurales y la aplicación de estrictos requerimientos de fuego. Asimismo, en ambos sectores existe un interés creciente en el uso de materiales compuestos de matriz orgánica por sus excelentes prestaciones, ligereza y comportamiento en servicio. Tradicionalmente, se han aplicado cargas anti-fuego a la matriz orgánica, disminuyendo sus propiedades mecánicas de forma importante. En este artículo se presentará un estudio de materiales compuestos formados por tres matrices orgánicas diferentes y cuatro tipos de fibras de carbono. Con estos constituyentes se han fabricado diferentes laminados para analizar, por un lado, la procesabilidad de estas resinas, y, por otro, la compatibilidad de estas resinas con las fibras de refuerzo utilizadas. Este estudio es necesario debido a que al tratarse de resinas formuladas con características frente a fuego y humos, su fabricabilidad puede presentar problemas más complejos que en las resinas convencionales