Altimeter height measurement errors introduced by the presence of variable cloud and rain attenuation

It has recently been recognized that spatially inhomogeneous clouds and rain can substantially affect the height precision obtainable from a spaceborne radar altimeter system. Through computer simulation, it has been found that typical levels of cloud and rain intensities and associated spatial variabilities may degrade altimeter precision at 13.5 GHz and, in particular, cause severe degradation at 35 GHz. This degradation in precision is a result of radar signature distortion caused by variable attenuation over the beam limited altimeter footprint. Because attenuation effects increase with frequency, imprecision caused by them will significantly impact on the frequency selection of future altimeters. In this paper the degradation of altimeter precision introduced by idealized cloud and rain configurations as well as for a realistic rain configuration as measured with a ground based radar is examined

Multiscale technique for the analysis of 3D-printed materials

The mechanical behaviour of structural elements made of 3D-printed materials is numerically investigated. With this aim a multiscale approach that allows to determine the macroscopic response, as depending on the material heterogeneity at the microscale level, is conceived. A non-linear laminate finite element that employs a reduced homogenization technique at each integration Gauss point is developed. In detail, the Piecewise Uniform Transformation Field Analysis is implemented. In order to validate the procedure, some numerical applications are developed. The obtained results are compared with evidence of experimental tensile and bending tests, available in literature. The application of a multiscale strategy, employing a reduced order method at the Gauss point level for the analysis of 3D-printed structural elements, could represent a good compromise in terms of accuracy of the results and computational efficiency

Modelling of damage and plasticity phenomena in 3D printed materials via a multiscale approach

A multiscale technique able to describe the overall mechanical response of 3D printed materials taking into account the plastic behaviour and the occurrence of failure is presented. Reference is made to elements produced by extrusion-based additive manufacturing. At the microscale, the de-cohesion between filaments that constitute the printed material is described introducing a cohesive damage interface model that also takes into account the unilateral contact. The micromechanical problem is solved with a homogenization procedure based on the PieceWise Uniform Transformation Field Analysis properly extended to the case of interfaces. In detail, the plastic strains in the filaments and the inelastic relative displacements along the interfaces are approximated as piecewise constant functions and then are computed solving the evolutive problem. Some numerical applications are carried out, comparing the numerical results with the experimental ones and with results obtained from non-linear finite element analyses, to show the potentiality of the proposed multiscale technique

Computational homogenization of 3D printed materials by a reduced order model

The aim of this paper is to study the effective mechanical behavior of 3D printed materials. To this purpose a micromechanical study is developed in order to investigate the influence of the heterogeneity of the 3D printed material at the microscale on the overall response. A reduced order model, usually adopted for the analysis of heterogeneous materials, is extended to model the response of the printed material, considered as periodic. In particular, the Mixed Transformation Field Analysis (MxTFA), based on a mixed-stress variational formulation of the elasto-plastic theory, considering the inelastic strain based on a representation of the self-equilibrated stresses, is developed. A unit cell, representative of the 3D printed material's microstructure, comprising a fiber and interstitial voids is defined and divided in subsets. In each subset, a self-equilibrated stress is considered introducing a constant, linear, or quadratic approximation and the plastic multiplier is assumed constant. Some numerical applications are developed considering different unit cells and different loading conditions. The obtained results are compared with some experimental results, available in literature, and with results obtained from non-linear finite element analyses. The application of a TFA-based method to the 3D printed materials could provide an effective tool for the prediction of the mechanical behavior with a significant reduction of the history variables defining the evolution problem

Mechanical properties of 3D printed polylactic acid elements: Experimental and numerical insights

The mechanical behaviour of polylactic acid (PLA) samples printed via material extrusion is experimentally and numerically addressed. An experimental program comprising tensile and three-point bending tests is carried out. Some filament printing orientations and different values of flow rate percentage are considered and their influence on the mechanical performance is investigated. From a numerical point of view, a new two-level model for the multiscale analysis is considered. The macroscopic structural behaviour of the 3D printed component is described with a laminate finite element model based on the first-order shear deformation theory. Each layer of the laminate is described with an elasto-plastic constitutive law and the geometrical and mechanical properties are derived from the experimental results. The micromechanical analysis is conducted only when inelastic strain occurs performing a non-linear analytical homogenization technique based on the Transformation Field Analysis. The obtained numerical results are compared with the experimental results highlighting the effectiveness of the proposed modelling approach

Effectiveness of some technical standards for debonding analysis in FRP-concrete systems

Debonding failure is a key issue in strengthening and retrofitting of existing concrete structures via fiber-reinforced polymers (FRP). In this paper, strength models proposed by different technical guidelines for predicting the debonding load and the effective bond length in FRP-concrete systems are consistently summarized and compared. By referring to the recent specialized literature, a wide database of experimental data - collected from debonding tests associated to FRP based on carbon, glass and basalt fibers - is defined and analyzed. As a result, soundness and effectiveness of some available technical indications are critically assessed, by highlighting the influence of both FRP stiffness (mainly related to the fiber type) and FRP application system. Moreover, a least-square-fitting calibration of theoretical predictions with respect to the experimental evidence is proposed and applied, resulting in the definition of a novel set of values for the empirical correction coefficients occurring in the analyzed strength models. Accordingly, proposed results pave the way towards the effective refinement of actual technical standards for debonding analysis in FRP-concrete systems

TECHNICAL STANDARDS FOR DEBONDING IN FRP-CONCRETE SYSTEMS: AN EXPERIMENTAL CONTRIBUTION FOR BASALT-FRP

Fiber-reinforced polymers (FRPs) are widely used in civil-engineering field for strengthening and retrofitting existing concrete structures. In the context of strengthened RC beams subjected to bending loads, a critical issue is the FRP debonding, mainly consisting in a brittle failure mechanism. In this paper, analytical relationships proposed by different technical standards and guidelines, are consistently summarized and compared. In particular, a wide database of experimental results obtained from debonding tests, and available in the recent literature, is reported and discussed. Moreover, experimental results obtained via 42 double shear tests on basalt-based FRP (BFRP) sheets attached on concrete supports are presented. In this light, soundness and effectiveness of available technical relationships, mainly proposed for FRP-concrete systems, based on carbon, glass and aramid fibers, are critically discussed with reference to the use of BFRP

Basalt-based fiber-reinforced materials and structural applications in civil engineering

In the last decades, a growing interest in using basalt as reinforcement for composite materials has emerged, since promising physico-chemical and mechanical properties of basalt products, as well as good processability features and cost-effectiveness of the corresponding production technologies. In particular, basalt fibers allow to define composite materials really competitive with those obtained by employing traditional glass or carbon fibers. Recent experimental programs and analytical approaches reveal that basalt-based fiber-reinforced materials may be effective for a number of structural applications in civil engineering. Depending on the fiber treatment and arrangement, as well as on the matrix type (polymeric or cementitious) different composite materials have been conceived. For instance, strengthening and retrofitting of existing structures (both concrete and masonry) may be performed through basalt-based fiber-reinforced polymers (BFRP) and cementitious matrices (BFRCM), as well as novel design concepts can be exploited by referring to basalt-based rebars and fiber-reinforced concrete (BFRC). This paper aims to furnish a systematic review of the state of the art on basalt fibers, basalt-based composite materials and their applications in civil engineering field, by tracing main available evidence and highlighting perspective aspects and open problems

Elasto-damage mechanics of osteons: A bottom-up multiscale approach

In this paper, a multiscale rationale is applied to develop a bottom-up modelling strategy for analysing the elasto-damage response of osteons, resulting in a first step towards a refined mechanical description of cortical bone tissue at the macroscale. Main structural features over multiple length scales are encompassed. A single osteon is described by considering a multi layered arrangement of cylindrical lamellae and accounting for both lacunar micro-voids and thin interlamellar regions, these latter modelled as soft interfaces. A multi-step homogenization procedure has been conceived and numerically applied to describe the equivalent mechanical response of osteon constituents, upscaling dominant subscale mechanisms. A progressive stress based damage approach has been implemented via a finite-element technique, allowing to describe interlaminar and/or intralaminar brittle failure modes. Proposed approach has been successfully validated by numerically reproducing available experimental tests of isolated osteons under different loading conditions. Present histologically-oriented multiscale model revealed to be sound and consistent, opening towards further insights about the influence on bone biomechanics of through-the-scales biophysical/biochemical alterations, possibly related to ageing or diseases