Damage evolution in a bonded nonwoven glass fiber network under cyclic compression

This study is concerned with nonwoven materials are made of network of glass fibers and consolidated by local bonds, such as geometric entanglement, local thermal fusion, or chemical binders. The objective of the study is to gain understanding of the damage accumulation processes during cyclic compression. The micromechanisms of damage during tensile loading of nonwoven materials have widely been studied and it is found that fiber–fiber bond failure followed by frictional sliding between fiber bundles, leading to the localization of damage is a dominant failure mechanism. However, the fracture mechanism a fiberglass network under compression is less understood. The compressive load response is nonlinear due to fiber-to-fiber contact. Comparing microCT images of samples before and after loading, we infer that fiber fracture is the dominant failure mechanism. Based on these observations, we hypothesize that the damage accumulation under cyclic compressive loading emerges indeed from fiber fracture, but that due to the accumulations of such fractures, high-stress locations are successively eliminated from the microstructure. In order to establish the validity of the hypothesis, the study reports on cyclic loading experiments on a range of strain ranges, in combination with acoustic emission measurements, as well as on a computational modeling effort. Strain-controlled cyclic (low-cycle fatigue) compression tests were carried out on samples of extracted from nonwoven fiberglass mats to determine the evolution of the stress–strain response and the degradation of the material. A global damage variable, D, is introduced to account for the change in modulus with cycle number N. It was found that the degradation is well described by with the degradation exponential k. It was found that although the modulus exhibits noticeable interspecimen variation, k remained consistent for multiple specimens from the same material system; however, it is dependent on the applied strain. In order to further elucidate the fracture mechanism of the fiber network associated with the global strain, in-situ investigation by monitoring the fiber fracture in the structure with the strain history is hereby proposed using acoustic emission (AE) detection technique. In contrast to AE where the system is directly coupled to the sample, here the AE signal is acquired indirectly via the load platens. Based on microCT imaging, the association between acoustic events and fiber fracture can be made. The measurements therefore allow us to link the damage onset with global strain and the influence of AE activity level during multiple load cycles on the material deterioration. Finite element models based on microCT images are used in conjunction with the XFEM approach to further obtain insight into the damage accumulation process. This approach will finally enable us to provide an explanation for the damage evolution law

Carbon nanotubes affect the toxicity of CuO nanoparticles to denitrification in marine sediments by altering cellular internalization of nanoparticle

Denitrification is an important pathway for nitrate transformation in marine sediments, and this process has been observed to be negatively affected by engineered nanomaterials. However, previous studies only focused on the potential effect of a certain type of nanomaterial on microbial denitrification. Here we show that the toxicity of CuO nanoparticles (NPs) to denitrification in marine sediments is highly affected by the presence of carbon nanotubes (CNTs). It was found that the removal efficiency of total NOX−-N (NO3−-N and NO2−-N) in the presence of CuO NPs was only 62.3%, but it increased to 81.1% when CNTs appeared in this circumstance. Our data revealed that CuO NPs were more easily attached to CNTs rather than cell surface because of the lower energy barrier (3.5 versus 36.2 kT). Further studies confirmed that the presence of CNTs caused the formation of large, incompact, non-uniform dispersed, and more negatively charged CuO-CNTs heteroaggregates, and thus reduced the nanoparticle internalization by cells, leading to less toxicity to metabolism of carbon source, generation of reduction equivalent, and activities of nitrate reductase and nitrite reductase. These results indicate that assessing nanomaterial-induced risks in real circumstances needs to consider the “mixed” effects of nanomaterials

Femtosecond laser nanostructuring in glass with sub-50nm feature sizes

We report on controllable production of nanostructures embedded in a porous glass substrate by femtosecond laser direct writing. We show that a hollow nano-void with a lateral size of ~40 nm and an axial size of ~1500 nm can be achieved by manipulating the peak intensity and polarization of the writing laser beam. Our finding enables direct construction of 3D nanofluidics inside glass.Comment: 15 pages, 4 figure

Maize nutrient uptake affected by genotype and fertilization

The content of nutrients in maize are commonly related with fertilization and soil quality and rarely explained with the individual hybrid properties. Therefore, the aim of this study is to access a long term fertilization system on ear leaf of Mg, Fe, Mn and Cu content in six maize hybrids(NS 3014, NS 4015, NS 5043, NS 6010, NS 6030 and NS 7020). Samples were collected from a long-term experiment at the Rimski Sancevi experimental field of the Institute of Field and Vegetable Crops in Novi Sad. The study included maize monoculture and 2-year rotations with the application of NPK and manure. Results showed that ear Mg content was influenced with the treatments, hybrid and their interaction and ranged from 1.77-2.69 g kg(-1). Iron variability was significantly affected with the treatments and interaction (hybrid x treatments) in range from 103.2 to 151.9g kg(-1). The ear manganese content (41.1-63.6g kg(-1)) derived from treatments and hybrid effect and Cu (12.3-23.6 g kg(-1)) was significantly influenced with treatments. Across all treatments, in average, NS6030 had higher values of nutrient and NS3014 was lower in ear nutrient content. This indicates that vegetation length could favor nutrient accumulation. Obtained results suggested that even on fairly productive soil such as Chernozem hybrid selection and the balanced fertilization is crucial for managing the maize nutrient content