Fatigue improvement and residual stress relaxation of shot-peened alloy steel DIN 34CrNiMo6 under axial loading

Shot-peening treatment was applied to a quenched and tempered DIN 34CrNiMo6 steel to improve its high-cycle R: -1 axial fatigue strength. Compared with the machined condition, the increase in the fatigue limit was 21.8%. S-N curves for shot-peened and the as machined condition were presented and compared with those obtained in previous research for rotating bending fatigue, including curves for mirror-polished specimens. The applied shot-peening treatment in this work (I-sp: 8A and 200% coverage) for quenched and tempered (Q + T) DIN 34CrNiMo6 steel introduced a compressive residual stress field and an increase in surface roughness, as well as minor variations in microstructure, hardness and the FWHM (full width of the diffraction peak at half maximum intensity) parameter. The introduced compressive residual stress field tended to reduce when an external stress is applied. This was due to the onset of plastic strain. In this paper, two types of quasi-static tests were conducted by applying an axial stress with six different magnitudes and in the two directions (compressive or tensile). This was in order to assess their influence on the relaxation of surface residual stresses. Due to the introduced compressive residual stresses, if the applied stress was compressive, the onset of plastic deformations was achieved with a lower stress magnitude. In addition, surface residual stress relaxation under cyclic applied stress was evaluated at four different stress magnitudes. Due to the cyclic-softening behaviour of this Q + T steel, its cyclic mechanical properties must be considered to assess the onset of plastic strains. With the experimental data, a logarithmic model to predict the evolution of surface residual stresses with the number of cycles for different applied stress magnitudes was presented.The authors wish to acknowledge the financial support received from the Department of Research and Development of the Basque Government, the UPV/EHU University, through the Research Project Reference: Grupos GV IT947-16

Cytotoxicity and Inflammatory Effects of Chitin Nanofibrils Isolated from Fungi

Fungal nanochitin can assist the transition from the linear fossil-based economy to a circular biobased economy given its environmental benefits over conventional crustacean-nanochitin. Its real-world implementation requires carefully assessing its toxicity so that unwanted human health and environmental issues are avoided. Accordingly, the cytotoxicity and inflammatory effects of chitin nanofibrils (ChNFs) from white mushroom is assessed. ChNFs are few nanometers in diameter, with a 75.8% N-acetylation degree, a crystallinity of 59.1%, and present a 44:56 chitin/glucan weight ratio. Studies are conducted for aqueous colloidal ChNF dispersions (0–5 mg·mL–1) and free-standing films having physically entangled ChNFs. Aqueous dispersions of chitin nanocrystals (ChNCs) isolated via hydrochloric acid hydrolysis of α-chitin powder are also evaluated for comparison. Cytotoxicity studies conducted in human fibroblasts (MRC-5 cells) and murine brain microglia (BV-2 cells) reveal a comparatively safer behavior over related biobased nanomaterials. However, a strong inflammatory response was observed when BV-2 cells were cultured in the presence of colloidal ChNFs. These novel cytotoxicity and inflammatory studies shed light on the potential of fungal ChNFs for biomedical applications.E.L. acknowledges the funds from the “2021 Euskampus Missions 1.0. Programme” granted by Euskampus Fundazioa and from the University of the Basque Country (Convocatoria de Ayudas a Grupos de Investigación GIU21/010). The authors also acknowledge the Open Access funding provided by the University of Basque Country (UPV/EHU). A.L. is thankful for funds from the Basque Government, Department of Education (IT-1766-22). C.B.A. acknowledges the predoctoral grant from the UPV/EHU. Maria Angela Motta and Dr. Upashi Goswami are acknowledged for their support in cell culture

Numerical characterization of local and global non-uniformities in the load distribution in ball screws

Load distribution in ball screws is a representation of the ball contact stress, and it is fundamental to understanding the behavior of these machine elements. This work aims to conduct a multi-variable analysis of the load distribution in ball screws. For this purpose, a numerical tool is developed for the generation and calculation of ball screw finite element (FE) models, which has been validated against the state of the art. This tool is based on the combination of an analytical contact model and the use of high-order FE models for the analysis of the load distribution of ball screws and stands out for its accuracy (less than 1% error against high-order FE models), adaptability, versatility (models are generated with more than 20 design variables and they can be introduced as components in larger models) and efficiency (being the computational time 1.25% of that of a high-order FE models) with respect to other existing models. Many different design variables (number of start threads, pitch, contact angle, ball size, slenderness and load arrangement) are studied in order to obtain a general characterization of the morphology of the load distribution in ball screws. Among them, the most influential variables on the load distribution and therefore on the structural behavior of ball screws are, load arrangement (with ratio r variations of up to 25% on the same ball screw) and slenderness (with ratio variations of up to 13% on ball screws with two turns of difference). The two most characteristic features, the non-uniformity at a local and global level are identified, along with as the possible causes of their appearance and the consequences that they may cause

Role of Inorganic Fillers on the Physical Aging and Toughness Loss of PLLA/BaSO4 Composites

The addition of inorganic fillers has been reported to increase the toughness of poly(l-lactide) (PLLA), but the effect of physical aging in such composites has been neglected. The present work discusses the effect of the still ongoing segmental relaxation in PLLA-based composites filled with BaSO4 inorganic particles in regard of the filler quantity. By means of differential scanning calorimetry, X-ray diffraction, and tensile testing of progressively aged PLLA filled with particles ranging from 0.5–10 wt %, we observed an increase in the mechanical energy required to activate the plastic flow of the primary structure in the PLLA matrix, which resulted in the embrittlement of the majority of composites upon enough aging. Results further clarify the role of debonding in the activation process of PLLA, and the behavior of the composite is described at the segmental level. Only an addition of 10% of particles has effectively preserved a ductile behavior of the samples beyond 150 aging days; therefore, we strongly remark the significance of studying the effect of physical aging in such composites.The authors thank funding from the Basque Government (GV/EJ)-Department of Education, University and Research (consolidated research groups IT-1766-22 GIC21/131) and grant PID2019-106236 GB-I00 funded by MCIN/AEI/10.13039/501100011033 and PID2022-139821OB-I00 funded by MCIN/AEI/10.13039/501100011033 and “ERDF A way of making Europe”. The Basque Government (GV/EJ) predoctoral grant for X.L. and SGIker technical services (UPV/EHU) for XRD and SEM support is also acknowledged

Resource preference of two stream detritivores in the laboratory largely differs from the supply of detritus below eucalypt plantations

Detritivores are pivotal in forest streams as they process detritus and promote secondary production. Many studies have addressed the preference of freshwater detritivores towards materials of differing quality. Nevertheless, few studies compare the resource preferences in the laboratory with the availability in the field. In the present study, feeding preferences of two stream detritivores (the caddisfly Sericostoma pyrenaicum and the amphipod Echinogammarus tarragonensis), over three native leaf species (alder, chestnut and oak) and an exotic species (eucalypt) were quantified in the laboratory. Preference for eucalypt leaves conditioned for 1, 2 and 3 weeks was also described. We then contrasted the preference patterns in the laboratory feeding experiments with a 15-month-long benthic standing stock time series of a stream below a native deciduous forest and another below a eucalypt plantation. Both detritivores preferred consuming alder leaves and more conditioned eucalypt leaves, although the amphipod was more selective than the caddisfly. The consumption preference in the laboratory was unmatched by the availability in the field, especially under eucalypt plantations and for the amphipod. Our results show that the strength of the preference for high-quality resources can differ among different taxa, which can modulate their response to land use changes.Open Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature. This study was funded by the Spanish Dirección General de Enseñanza Superior e Investigación Científica (Project DGESIC PB98-0151) and finanacial support in terms of a predoctoral Grant to A. Otermin from Basque Government

Habitat complexity in aquatic microcosms affects processes driven by detritivores

LF was supported in part by the Spanish Ministry of Economy and Competitiveness through the project SCARCE Consolider-Ingenio CSD2009-00065.Habitat complexity can influence predation rates (e.g. by providing refuge) but other ecosystem processes and species interactions might also be modulated by the properties of habitat structure. Here, we focussed on how complexity of artificial habitat (plastic plants), in microcosms, influenced short-term processes driven by three aquatic detritivores. The effects of habitat complexity on leaf decomposition, production of fine organic matter and pH levels were explored by measuring complexity in three ways: 1. as the presence vs. absence of habitat structure; 2. as the amount of structure (3 or 4.5 g of plastic plants); and 3. as the spatial configuration of structures (measured as fractal dimension). The experiment also addressed potential interactions among the consumers by running all possible species combinations. In the experimental microcosms, habitat complexity influenced how species performed, especially when comparing structure present vs. structure absent. Treatments with structure showed higher fine particulate matter production and lower pH compared to treatments without structures and this was probably due to higher digestion and respiration when structures were present. When we explored the effects of the different complexity levels, we found that the amount of structure added explained more than the fractal dimension of the structures. We give a detailed overview of the experimental design, statistical models and R codes, because our statistical analysis can be applied to other study systems (and disciplines such as restoration ecology). We further make suggestions of how to optimise statistical power when artificially assembling, and analysing, ‘habitat complexity’ by not confounding complexity with the amount of structure added. In summary, this study highlights the importance of habitat complexity for energy flow and the maintenance of ecosystem processes in aquatic ecosystems.Publisher PDFPeer reviewe

The effect of sieve mesh size on the description of macroinvertebrate communities

Considerable time and effort is required to estimate the abundance and biomass of benthic macroinvertebrates, and often variable mesh size sieves are used to clean collected samples. We test whether the use of a mesh with a 1 mm pore size is adequate to obtain a valid description of a benthic macroinvertebrate community. Stream benthic surber samples were collected from 24 headwater streams. The densities, biotic indices and biological traits ofmacroinvertebrates retained in al mm mesh ('> 1 mm' fraction) were compared to the same descriptors for the of macroinvertebrates retained in a 0.5 mm mesh sieve ('total'). We found that, if only the large fraction (> 1 rnm) is examined, the cornmunity descriptors are affected. Nevertheless, the observed changes were proportional and predictable for all of the variables describing invertebrate communities. Statistical differenti­ation of the tested metrics between sites was similar for both mesh sizes. Depending on the aim of the study (e.g., environmental impact assessments), the use of a 1 mm mesh sieve would be sufficient in describing macroinvertebrate communities.Para las estimas de abundancia y biomasa, el procesado de las muestras en laboratorio de invertebrados bentónicos requiere un tiempo y esfuerzo considerable y generalmente implica el uso de tamices de diferente luz de malla para lavar la muestra. Nuestro trabajo trata de comprobar si es suficiente para una descripción válida de la comunidad el uso de un tamiz de malla de 1 mm de poro en el procesado de muestras. Con tal propósito se recogieron muestras bentónicas de río en 24 tramos de cabecera y se compararon densidades, índices bióticos y rasgos biológicos de los invertebrados que eran retenidos en un tamiz de luz de malla de 1 mm (fracción '>1 mm') con los obtenidos usando una de 0.5 mm ('total'). Nuestro estudio revela que el análisis exclusivo de la malla gruesa afecta a los descriptores de la comunidad. Sin embargo, los cambios observados son proporcionales para todas las variables y se pueden predecir bien con ecuaciones lineales. Por otro lado, la diferenciación estadística entre estaciones es similar usando ambos tipos de malla, lo que en definitiva sugiere que, dependiendo del objetivo del estudio (por ejemplo, evaluación de impacto ambiental), el examen de la fauna retenida en un tamiz de 1 mm de poro puede ser suficiente para la descripción de las comunidades de macroinvertebrados

Land use drives detritivore size structure and decomposition through shifts in resource quality and quantity

Land use change and nutrient pollution are two pervasive stressors that can modify carbon cycling, as they influence the inputs and the transformation of detritus. Understanding their impact on stream food webs and on diversity is particularly pressing, as streams are largely fuelled by detrital material received from the adjacent riparian environment. Here we assess how a switch from native deciduous forest to Eucalyptus plantations and nutrient enrichment alter the size distribution of stream detritivore communities and decomposition rates of detritus. As expected, more detritus resulted in higher size-independent, or overall, abundance (i.e. higher intercept of size spectra). This change in overall abundance was mainly driven by a change of the relative contribution of large taxa (Amphipoda and Trichoptera), which changed from an average relative abundance of 55.5 to 77.2 % between the sites compared for resource quantity differences in our study. In contrast, detritus quality modified the relative abundance of large vs small individuals (i.e. size spectra slopes), with shallow slopes of size spectra (proportionately more large individuals) associated with sites with nutrient-richer waters and steeper slopes (proportionately fewer large individuals) associated with sites draining Eucalyptus plantations. Decomposition rates of alder leaves due to macroinvertebrates increased from 0.0003 to 0.0142 when relative contribution of large organisms increased (modelled slopes of size spectra: −1.00 and − 0.33, respectively), highlighting the importance of large sized individuals for ecosystem functioning. Our study reveals that land use change and nutrient pollution can greatly impair the transfer of energy through the detrital or ‘brown’ food web by means of intra- and inter-specific responses to quality and quantity of the detritus. These responses enable linking land use change and nutrient pollution to ecosystem productivity and carbon cycling.This work was carried out with financial support from the EU Commission within the RivFunction project (contract EVK1-CT-2001-00088). AL acknowledges the financial support by the mobility program Ikermugikortasuna-2019 of the Basque Government

Thermal, structural and degradation properties of an aromatic-aliphatic polyester built through ring-opening polymerisation

The novel biodegradable aromatic–aliphatic polyester, poly(2-(2-hydroxyethoxy)benzoate), was explored through thermal analysis, X-ray diffraction, dynamic mechanical analysis and comparative bio and catalysed degradation.</p