Bottom-up manufacturing cost optimisation of composite aircraft structures: Manual layup vs. automated layup

This paper presents a novel methodology for the bottom-up manufacturing cost optimisation of composite aircraft structures for Automated Fibre Placement (AFP) techniques. The proposed bottom-up approach divides the manufacturing process into many individual activities, making it applicable to a wide range of composite aircraft structures. This approach also splits the costs into material, tool, machine, labour, and indirect costs, enabling the precise cost analysis of these structures. A numerical example, featuring a mono-stiff ener composite panel, is investigated. The manufacturing cost of manual layup is compared against that of automated layup. Results indicate that manual layup is superior, in terms of cost, for the manufacture of the mono-stiff ener composite panel, and that the safety of the panel can be signifi cantly improved with only a small 5% increase in manufacturing costs

Structural Analysis of Masonry Square Vaults in the Italian Region of Apulia

This research concerns the introduction and the structural analysis of masonry vaults in Puglia, a region in the south part of Italy, built between the sixteenth and the seventeen centuries. Such vaults have special shapes that make them unique in the overview of the masonry vaults spread all over the world. The present paper intends to shed light on the mechanical behavior of two typical vaults in Puglia, the “volta a spigoli” (edge vault) and the “volta a squadro” (square vault). There are many contributions that explore the mechanical behavior of the classical vaults, but to the authors’ knowledge, this is the first attempt investigating the “volta a squadro”. The paper describes the adopted research methods. First, a building survey is carried out with the integration of previous geometry acquisitions performed by local stakeholders. Then, the analysis is pursued by a non-linear approach that suitably inserts cracks where stress concentrations occur. Two meaningful load conditions are taken into account and numerically investigated. Under vertical loads, numerical results have inferred the surveyed cracks and concluded that the safety factor is much higher than one. On the other hand, under the maximum seismic load, the safety factor is estimated to be about 30%. This work is the very first investigation on the structural performance of a “volta a squadro”

Efficient and realistic 3-D Boundary Element simulations of underground construction using isogeometric analysis

The paper outlines some recent developments of the boundary element method (BEM) that makes it more user friendly and suitable for a realistic simulation in geomechanics, especially for underground excavations and tunnelling. The innovations refer to the introduction of isogeometric concepts, elasto-plastic analysis and the simulation of ground support. The introduction of isogeometric concepts for the description of the excavation boundaries results in less user and analysis effort, since complex geometries can be modelled with few parameters and degrees of freedom. No mesh generation is necessary. In order to consider heterogeneous and inelastic ground conditions a domain discretisation is used but the use of isogeometric methods results in a minimum of user effort. Efficient methods are also presented for modelling rock bolts. A comparison of results of test examples with other numerical methods and analytical solutions confirm the efficiency and accuracy of the proposed implementation. A practical example with a complex geometry is presented.Comment: 33 pages, 25 figures. arXiv admin note: text overlap with arXiv:2003.1021

Use of mannan oligosaccharides during "post-weaning enteric syndrome" in rabbits: effect on in vivo performance from 35 to 60 days

Four groups, each consisting of 684 weaned (35 days) hybrid Hyla rabbits were fed ad libitum the same commercial concentrate supplemented, respectively, with antibiotics (AGP group: colistin sulphate 144 mg/kg; tylosin 100m g/kg and oxytetracyclin 1000 mg/kg) or with mannan oligosac- charides (MOS) at 0.5 (group MOS_0.5), 1.0 (group MOS_1.0) and 1.5 g/kg (group MOS_1.5). Up to 60 days, mortality rate was recorded daily. For each group, 64 rabbits were controlled weekly for live weight to calculate daily weight gain (DWG). Feed intake (and, by consequence, feed conversion ratio) was measured, weekly, per group. No differences were observed for live weight during the trial, while DWG showed an alternate trend, in general, significantly lower for AGP group, exclusive of the third week (49- 56 days). Exclusive of the first week of the trial feed intake was higher for AGP than the other groups and the feed conversion ratio was more favourable for MOS groups. Mortality rate was significantly higher (34.2%) in AGP groups. The lowest mortality was recorded in MOS_1.0 group (7.75%)

A Cost Estimation Approach for Aircraft Design Enhancement

This paper presents a novel reliability-based parametric methodology for quantifying the reliability of cost estimates for new composite aircraft components. In recent years, the aircraft production sector has increased its attention on optimizing their composite manufacturing operations. It has become clear that a key factor in the success of these operations is the consideration that not only technical factors, but also economic ones as well are relevant. Composite manufacturing variability is greatly influenced by many of these factors, and since manufacturing with composites is significantly more difficult than with more traditional materials, there are many sources of uncertainty that could influence the reliability of manufacturing cost estimates for new composite aircraft components. Therefore, it is worth considering these sources of uncertainty during the cost estimation process and to quantify the reliability of the cost estimates. To demonstrate the proposed methodology, a numerical example featuring a real-life composite aircraft component from a Boeing 787, with real-life data, is presented. Results show that the proposed methodology can quantify the uncertainty associated with cost estimates for new composite aircraft components in an effective manner, thereby supporting engineers in optimising the cost of their designs, helping them avoid errors in budget definition, and enabling them to allocate resources more efficiently

Effect of spray application of Lactobacillus plantarum on in vivo performance, caecal fermentations and haematological traits of suckling rabbits

Two days before kindling, 228 New Zealand White rabbit does were homogeneously divided into two groups (114 does per group) and fed the same diet. After delivery, the litters were equalized to 8 pups. From 1 to 35 days of age (weaning), the control group (CONT) did not receive any treatment while in the experimental group (LAC) the nests were sprayed with a commercial product containing lyophilized Lactobacillus plantarum dissolved in water (12 g/L). L. plantarum was sprayed on the litters (5 mL per rabbit) once a day during seven consecutive days after delivery. After one week of rest, the treatment was repeated for another week according to the same experimental protocol. Mortality rate, recorded on all the litters (912 rabbits per group) was significantly lower in the LAC group (9.9 vs 17.2%; P<0.05). There were no significant differences in in vivo performance of the 24 litters per group, and rabbits of both groups reached a similar weight at weaning (938 vs 932 g for LAC and CONT groups, respectively). Rabbits from the LAC group showed fermentative activity of caecal microflora (total volatile fatty acids 24.8 vs 14.5 mmol/L; P<0.01) and higher percentage of lymphocytes (73.7 vs 63.9% of total white blood cells; P<0.05). Among the microflora population of rabbit caecal content from the LAC group, it was possible to identify L. plantarum (1.25x106 CFU/g). It might be supposed that the changes in caecal microflora can affect our results and improve the sanitary status of Lactobacillus-sprayed rabbits in the period 1-35 days of age

Local and nonlocal BEM damage analysis

Damage models are known to describe the accumulation of continuum damage, the initiation of micro cracks, and their coalescence to macro cracks. The increase of damage generally leads to a local softening behaviour. A local approach to such phenomena may lead to a physically unacceptable localisation of the deformation which gives a spurious mesh sensitivity of the numerical computation. The nonlocal integral type theory overcomes such deficiency. Only a few papers have been published applying the BEM to the nonlocal plasticity and damage. Following a recent paper, the author means to present some BEM results in continuum damage mechanics

Erratum to Arc-length procedures with BEM in physically nonlinear problems

In the present paper an erratum concerning the figures 2 and 12 of the paper "Arclength procedures in physically nonlinear problems" published in Engineering Analysis with Boundary Elements vol.28 issue 6pp.547-559, is given

Localisation analysis by BEM in damage mechanics

In this paper a thermodynamically consistent damage mechanic model is presented in the context of a boundary element formulation. In particular, the damage model of Lemaitre is considered. The boundary element method (BEM) is applied by introducing convenient inelastic strains which account for the irreversibly degeneration of the mechanical properties due to a diffused microcracking in the structure. The theoretical background of the model as well as the boundary element formulation are presented. The governing relations are first derived by the free energy potential fully complying with thermodynamic principles, then the flaw laws are obtained by assuming the existence of a damage activation function and under the hypothesis of generalised associative damage behaviour, finally numerical results are obtained by coupling suitably the BEM with the arclength methods

Il metodo degli elementi finiti di contorno nell'analisi non locale del danneggiamento (ex60% 2000-2002)

Obiettivo principale della presente ricerca è quello di fornire modelli teorici e numerici più sofisticati per l’analisi non lineare di opere in cls, c.a., muratura, cls e muratura fibrorinforzati e terre; modelli in grado di tener conto del danneggiamento, di prevedere con maggiore accuratezza i livelli limite di carico applicato e di guidare il progettista verso interventi di consolidamento strutturale più economici e razionali. Materiali quali il cls, la muratura e le terre, sotto carico crescente, possono presentare comportamenti non lineari la cui corretta modellazione può migliorare sensibilmente la progettazione strutturale, sia in termini economici che in termini di sicurezza. Al momento non esistono in commercio codici di calcolo consolidati e affidabili in grado di tener conto del comportamento non lineare softening di materiali quali quelli suddetti. Il lavoro condotto negli anni 2000 e 2001 si è concentrato quindi sul fenomeno descritto. Si sono analizzati gli approcci proposti in letteratura, se n’è avanzato uno semplificato come punto di partenza e si è cercato di programmare il tutto in un codice di calcolo agli elementi di contorno in grado di fornire i primi risultati numerici. La scrittura del programma in Fortran90 è tuttora in corso. Il programma di ricerca che si propone intende proseguire nel lavoro e prevede: il completamento dell’analisi teorica dei modelli di danneggiamento e dei relativi problemi di instabilità materiale; • il completamento del codice di calcolo agli elementi di contorno; • l’analisi critica dei risultati numerici ottenuti e il confronto con altre tecniche numeriche; l’arricchimento con modelli di danno più complessi in grado di cogliere le anisotropie del materiale; • l’analisi numerica di manufatti in cls, muratura e terre. • l’introduzione del codice BEM in programmi di calcolo commerciali (ABAQUS, Ansys, Nastran, ecc.); Esperienze numeriche e di laboratorio hanno mostrato che la zona danneggiata è di dimensioni limitate rispetto alle dimensioni globali del solido: un approccio agli elementi di contorno, perciò, potrebbe rivelarsi una scelta più appropriata, oltre che originale in virtù della quasi inesistente produzione scientifica in merito. L’approccio potrà far tesoro, inoltre, dell’esperienza acquisita dal sottoscritto sul metodo degli elementi di contorno negli ultimi sei anni sia presso il Wessex Institute of Technology (Southampton) sia presso il Queen Mary and Westfield College (Londra)