This work adds new experimental facts on room temperature hardness and flexural strength of alumina and composites with 1, 2, 5 and 10 vol.% single walled carbon nanotubes (SWNT) with similar grain size. Monolithic Al 2 O 3 and composites were spark plasma sintered (SPS) in identical conditions at 1300ºC, achieving high density, submicrometric grain size and a reasonably homogeneous distribution of SWNTs along grain boundaries for all compositions with residual agglomerates. Vickers hardness values comparable to monolithic alumina were obtained for composites with low (1 vol.%) SWNT content, though they decreased for higher concentrations, attributed to the fact that SWNT constitute a softer phase. Three point bending flexural strength also decreased with increasing SWNT content. Correlation between experimental results and microstructural analysis by electron microscopy indicate that although SWNT agglomerates have often been blamed for detrimental effects on the mechanical Manuscript Click here to download Manuscript: paper alumina para J Mat Sci -corregido (1).docx Click here to view linked References 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 2 properties of these composites, they are not the main cause for the reported decay in flexural strength.

Dense alumina composites with different carbon nanotube content were prepared by colloidal processing and consolidated by Spark Plasma Sintering (SPS). Single-wall carbon nanotubes (SWNTs) were distributed at grain boundaries and also into agglomerates homogeneously dispersed. Carrying out Vickers hardness tests on the cross-section surfaces instead of top (or bottom) surfaces has shown a noticeable increase in the reliability of the hardness measurements. This improvement has been mainly attributed to the different morphology of carbon nanotube agglomerates, which however does not seem to affect the Vickers hardness value. Composites with lower SWNT content maintain the Vickers hardness of monolithic alumina, whereas it significantly decreases for the rest of compositions. The decreasing trend with increasing SWNT content has been explained by the presence of higher SWNT 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 Heterogeneous dispersion and distribution of CNTs in the ceramic matrix, poor chemical compatibility between CNTs and alumina hindering effective transfer load and the large differences in the scales of the matrix microstructure and the carbon nanotubes have been stated as main obstacles to transfer the desirable CNT mechanical properties to the brittle ceramic matrix [5,7,11,14,15]. Adequate dispersion of CNTs is very difficult owing to their tendency to form bundles in order to minimize their surface area.Although aqueous colloidal processing has been assessed as an efficient technique producing adequate dispersion of CNTs throughout ceramic matrix grain boundaries after sintering [18][19][20], the presence of agglomerates seems to be unavoidable.Recently, Poorteman et al [21] fabricated MWNT/alumina composites with low MWNT content (0.6 and 1.4 vol. %) by a colloidal processing route to optimize electrostatic

The use of roundwood in structures has drawbacks that include tapering and lack of flatness, which can be overcome by making a longitudinal cut to flatten one side. The aim of this work was to compare the mechanical behavior of roundwood vs. roundwood with one flat face, comparing pieces of small-diameter roundwood from young trees of Pinus nigra Arnold. Half the samples were given a longitudinal cut. Specimens taken from these pieces were tested for bending and compression parallel to the grain to determine their modulus of elasticity and strength. The modulus of rupture by bending was 22% lower in roundwood with one flat face (59.0 MPa) than in roundwood (75.6 MPa). It has been observed that the smaller cross section in the roundwood with one flat face is not the only explanation for the decrease in the bending strength. In contrast, no significant differences were observed for the other three mechanical properties studied (compression strength parallel to the grain and modulus of elasticity in bending and compression).

Non-destructive testing was used to predict the static modulus of elasticity (MOES) of Scots pine (Pinus sylvestris) timber from the northeast of Spain. Three vibration tests were performed, longitudinal, flatwise and edgewise, to obtain the dynamic modulus of elasticity (MOEdyn) based on the fundamental resonant frequencies. The MOEdyn was additionally obtained from ultrasound tests. Measurements of different features were performed of the various samples, which were also subjected to a bending test to find the MOES. Different types of models, simple linear regression (SLR), multiple linear regression (MLR) and artificial neural network (ANN), were generated to predict the MOES based on the study variables. The predictive capacity of the different models was analysed by comparing the root mean square error (RMSE) obtained using the 10-fold cross-validation method. The vibration techniques showed a better MOES prediction than the ultrasound techniques. The MOEdyn obtained from the fundamental resonant frequency of the edgewise flexural vibration (MOEEV) was the variable that best predicted the MOES. The error of the SLR with MOEEV was not significantly improved by any other model, whether univariate or multivariate.The ANN-based models did not significantly improve the error of the MLR-based models.

Samples of wood from Populus × canadensis (9,5 % moisture) were treated with olive oil at 195 °C simultaneously with 15 % or 30 % compression densification, and the results were compared with samples subjected to oil heat treatment without densification, and control samples. The density of the treated samples increased by 18 %, 43 % and 1,5 % respectively, and barely changed over the six subsequent months stored inside the laboratory room (at approximately 65 % RH, 20 °C). This was due to the fact that the slight weight increment caused by the additional moisture content was offset by the increase in volume from the springback effect. When subjected to atmospheres with different relative humidities, the treated samples stabilised at the same time as the control samples, although the treated samples had a significantly lower moisture absorption than the control samples. It was also observed that the hygroscopic shrinkage in oil heat densification treatment samples was approximately half those of the control samples. The initial densification was partially lost as a result of springback: approximately 3 % in the first springback at a relative humidity of 65 % RH, and an additional 4 % in the second springback to a relative humidity of 85 % RH. Once this latter relative humidity had been attained, no new losses in densification were observed. The ageing of the oil used in the treatment caused a slight loss of densification in the densest samples.