Artificial Stress Research Articles

Impact of Short-term Artificial Low Salinity Stress on the Flavor Quality of Scylla Paramamosain

Scylla paramamosain is a kind of large euryhaline marine crab. As an important physicochemical parameter of seawater, salinity has a great impact on the survival, growth and quality of Scylla paramamosain. This research tested the content of non-volatile flavor substance, lactic acid and taurine on the 0, 1st, 3rd, 7th and 15th day in three salinity gradients (3, 13, 23) with HPLC (High-performance Liquid Chromatography) technology. Results have shown that in low salinity stress, the cumulative amount of free amino acids in muscle of Scylla paramamosain is more than that in hepatopancreas, while the cumulative amount of essential amino acids in hepatopancreas is more than that in muscle. In muscle, contents of three flavor amino acids are ranked as follows: sweet, bitter and delicious amino acid, and in hepatopancreas, it is bitter, sweet and delicious amino acid. The fluctuation rule of free amino acid, essential amino acid and lactic acid in Scylla paramamosain in the low salinity group is similar to that of other salinity control group, while the content of sweet amino acid, bitter amino acid, nucleotide, EUC, taurine is different from that of other salinity control groups.

A large-scale study of stress, emotions, and blood pressure in daily life using a digital platform

Stress is often associated with pathophysiologic responses, like blood pressure (BP) reactivity, which when experienced repeatedly may be one pathway through which stress leads to poor physical health. Previous laboratory and field studies linking stress to physiological measures are limited by small samples, narrow demographics, and artificial stress manipulations, whereas large-scale studies often do not capture measures like BP reactivity in daily life. We examined perceived stress, emotions, heart rate, and BP during daily life using a 3-wk app-based study. We confirmed the validity of a smartphone-based optic sensor to measure BP and then analyzed data from more than 330,000 daily responses from over 20,000 people. Stress was conceptualized as the ratio of situational demands relative to individual resources to cope. We found that greater demands were associated with higher BP reactivity, but critically, the ratio of demands relative to resources improved prediction of BP changes. When demands were higher and resources were lower, there was higher BP reactivity. Additionally, older adults showed greater concordance between self-reported stress and physiologic responses than younger adults. We also observed that physiologic reactivity was associated with current emotional state, and both valence and arousal mattered. For example, BP increased with high-arousal negative emotions (e.g., anger) and decreased with low-arousal positive emotions (e.g., contentment). Taken together, this work underscores the potential for expanding stress science and public health data using handheld phones to reliably and validly measure physiologic responses linked to stress, emotion, and physical health.

Effects of Throughfall Exclusion on Photosynthetic Traits in Mature Japanese Cedar (Cryptomeria japonica (L. f.) D. Don.)

As climate change progresses, it is becoming more crucial to understand how timber species respond to increased drought frequency and severity. Photosynthetic traits in a 40-year-old clonal Japanese cedar (Cryptomeria japonica) plantation were assessed under artificial drought stress using a roof to exclude rainfall and a control with no exclusion. C. japonica is a commercial tree that is native to Japan and has high growth on mesic sites. The maximum carboxylation rate (Vcmax), maximum electron transfer rate (Jmax), and dark respiration rate (Rd) in current-year shoots in the upper canopy were determined from spring to autumn over two growing seasons. In addition, the photosynthetic rate at light saturation (Pmax), stomatal conductance (gs), and intrinsic water use efficiency (WUEi) were measured in the morning and afternoon during the same period. Leaf mass per unit area (LMA) and nitrogen concentration (N) were also measured. The values of Vcmax, Jmax, Rd, N, and LMA did not differ between the two plots. By contrast, significantly lower Pmax and gs and higher WUEi were found in the drought plot, and the reduction in Pmax was accompanied by low gs values. Midday depressions in Pmax and gs were more pronounced in the drought plot relative to the control and were related to higher WUEi. Under drought conditions, mature Japanese cedar experienced little change in photosynthetic capacity, foliar N, or LMA, but they did tend to close the stomata to regulate transpiration, thus avoiding drought-induced damage to the photosynthetic machinery and improving WUEi.

Development of stable transgenic maize plants tolerant for drought by manipulating ABA signaling through Agrobacterium-mediated transformation

BackgroundIn crop plants, to cope up with the demand of food for rising population, revolutionary crop improvement programmes are being implemented for higher and higher yields. Abiotic stress, especially at flowering stage, causes drastic effect on yield in plants. Deforestation and urbanization made the water table very low and changed the climate which led to untimely and unforeseen rains which affect the yield of a crop through stress, both by lack of water as well as water logging (abiotic stress). Development of tolerant plants through breeding is a time-consuming programme and does not perform well in normal conditions. Development of stress-tolerant plants through transgenic technology is the better solution. Maize is a major crop used as food and fodder and has the commercial value in ethanol production. Hence, the genes viz., nced (9-cis-epoxycarotenoid dioxygenase) and rpk (receptor-like protein kinase), which play the key roles in the abscisic acid pathway and upstream component in ABA signaling have been transferred into maize plants through Agrobacterium-mediated transformation by optimizing several parameters to obtain maximum frequency of transformation. ResultsCultures raised from immature embryos of 2-mm size isolated from maize cobs, 12–15 days after pollination, were used for transformation. rpk and nced genes under the control of leaP and salT promoters respectively, cloned using gateway technology, have been introduced into elite maize inbred lines. Maximum frequency of transformation was observed with the callus infected after 20 days of inoculation by using 100 μM acetosyringone, 10 min infection time, and 2 days incubation period after co-cultivation resulted in maximum frequency of transformation (6%) in the NM5884 inbred line. Integration of the genes has been confirmed with molecular characterization by performing PCRs with marker as well as gene-specific primers and through southern hybridization. Physiological and biochemical characterization was done in vitro (artificial stress) and in vivo (pot experiments). ConclusionsChanges in the parameters which affect the transformation frequency yielded maximum frequency of transformation with 20-day-old callus in the NM5884 inbred line. Introducing two or more genes using gateway technology is useful for developing stable transgenic plants with desired characters, abiotic stress tolerance in this study.

Evaluating the Association Between Artificial Sweetener Intake and Indicators of Stress and Anxiety.

The purpose of this study was to evaluate the association between non-nutritive sweetener (NNS) consumption and stress and anxiety, among a sample of college students. Two-hundred and twenty-seven students from a large mid-western university participated in this cross-sectional study. Students completed an online survey that evaluated NNS using a validated food frequency questionnaire. Stress and anxiety were evaluated using previously validated instruments. Most students reported very low/low/average concern for stress (63.9%), and had low/moderate anxiety (82.3%). Participants experiencing high and very high levels of stress had significantly higher NNS consumption compared to those with a very low and low risk, and concern for stress (p < .046; d = 0.28). There was no difference however for NNS intake and anxiety. Reduction of artificial sweetener intake may be associated with stress levels among college students. However, more research is needed to examine any causal relationship between artificial sweetener intake and stress.

Effects of Soil Amendment With Wood Ash on Transpiration, Growth, and Metal Uptake in Two Contrasting Maize (Zea mays L.) Hybrids to Drought Tolerance.

Wood ash as a soil amendment has gained wide spread acceptance in the recent years as a sustainable alternative to chemical fertilizers, although information regarding the effects of its application on maize growth and yield in the context of climate change and increasing drought severity is lacking till date. In the present study, field and pot trials were carried out at the experimental farm of the University of Padova at Legnaro (NE Italy) in a silty-loam soil in order to investigate the effects of soil amendment with wood ash (0.1% w/w, incorporated into the 0.2-m top soil) on the bioavailability of mineral elements and their uptake by maize. Characteristics analyzed included plant growth, leaf transpiration dynamics, and productivity in two contrasting hybrids, P1921 (drought sensitive) and D24 (drought tolerant). Wood ash contained relevant amounts of Ca, K, Mg, P, and S, and hazardous levels of Zn (732 mg kg−1), Pb (527 mg kg−1), and Cu (129 mg kg−1), although no significant changes in total soil element concentration, pH, and electrical conductivity were detected in open field. Ash application led to a general increasing trend of diethylene triamine penta-acetic acid (DTPA)-extractable of various elements, bringing to higher grain P in D24 hybrid, and Zn and Ni reductions in P1921 hybrid. Here, the results demonstrated that ash amendment enhanced shoot growth and the number of leaves, causing a reduction of harvest index, without affecting grain yield in both hybrids. The most relevant result was a retarded inhibition of leaf transpiration under artificial progressive water stress, particularly in the drought-tolerant D24 hybrid that could be sustained by root growth improvements in the field across the whole 0–1.5 m soil profile in D24, and in the amended top soil in P1921. It is concluded that woody ash can be profitably exploited in maize fertilization for enhancing shoot and root growth and drought tolerance, thanks to morphological and physiological improvements, although major benefits are expected to be achieved in drought tolerant hybrids. Attention should be payed when using ash derived by metal contaminated wood stocks to avoid any health risk in food uses.

Supply chain resilience for vaccines: review of modeling approaches in the context of the COVID-19 pandemic

PurposeDespite rapid success in bringing SARS-CoV-2 vaccines to distribution by multiple pharmaceutical corporations, supply chain failures in production and distribution can plague pandemic recovery. This review analyzes and addresses gaps in modeling supply chain resilience in general and specifically for vaccines in order to guide researchers and practitioners alike to improve critical function of vaccine supply chains in the face of inevitable disruptions.Design/methodology/approachSystematic review of the literature on modeling supply chain resilience from 2007 to 2020 is analyzed in tandem with the vaccine supply chain manufacturing literature. These trends are then used to apply a novel matrix analysis to seven Securities and Exchange Commission (SEC) annual filings of pharmaceutical corporations involved in COVID-19 vaccine manufacture and distribution.FindingsPharmaceutical corporations favor efficiency as they navigate regulatory, economic and other threats to their vaccine supply chains, neglecting resilience – absorption, adaptation and recovery from inevitable and unexpected disruptions. However, explicitly applying resilience analytics to the vaccine supply chain and further leveraging emerging network science tools found in the academic literature, such as artificial intelligence (AI), stress tests and digital twins, will help supply chain managers to better quantify efficiency/resilience tradeoffs across all associated networks/domains and support optimal system performance post disruption.Originality/valueThis is the first review addressing resilience analytics in vaccine supply chains and subsequent extension to operational management through novel matrix analyses of SEC Filings. The authors provide analyses and recommendations that facilitate resilience quantification capabilities for vaccine supply chain managers, regulatory agencies and corporate stakeholders and are especially relevant for pandemic response, including application to the SARS-CoV-2 vaccines.

Artificial Neural Network Plan for Transmission Tower Structure Safety Assessment

The security of transmission tower structure is the foundation to ensure the safe operation of power grid. The research of fuzzy qualitative assessment method for the structural health of transmission towers is the basic work of large-scale digital power grid engineering. In this paper, artificial neural network (ANN) is used as a generalized tool for structural health assessment of transmission towers. The feasibility of using artificial neural network to qualitatively evaluate the structural health of transmission towers is verified by numerical simulation data. In order to train the artificial neural network, the displacement, stress and other signals generated by the finite element model are calculated and used as the training input of the artificial neural network. The detailed stress results of the finite element model are calculated as the qualitative evaluation basis of the structural health, and the training output of the artificial neural network is generated. By the same method, the test set is generated, and it is found that the artificial neural network is feasible for the fuzzy qualitative assessment of the structural health of transmission tower, and the misstatement rate is less than 5%.

The influence of shale swelling on casing deformation during hydraulic fracturing

Casing deformations during hydraulic fracturing are a serious problem in the Weirong shale gas field. This study focuses on the mechanism of shale swelling-induced casing deformation. First, the characteristics of the casing deformations in the Weirong shale gas field were analyzed. Subsequently, the mechanism of shale swelling during immersion was investigated and numerical simulations were performed to investigate the effect of shale swelling on casing deformation. Finally, we discussed various countermeasures to suppress casing deformation. The results demonstrate that clay-swelling during immersion leads to the propagation and expansion of fractures along the beddings, thereby causing shale swelling. Furthermore, the casing stress increases with the increase in shale swelling. The swelling formation distributions have a significant effect on the type of casing deformation. Symmetric swelling formation distributions cause extrusion deformation, and asymmetric swelling formation distributions cause bending deformation, which is similar to the type of casing deformation observed in the WY 23–5 well in the Weirong shale gas field. Furthermore, shear deformation can also be induced if the dip angle of the swelling formation is less than 90°. Increasing the casing thickness and steel grade, and adjusting the Poisson's ratio of the cement sheath does not have a significant effect on suppressing shale swelling-induced casing deformation. The effect of cement quality on casing deformation depends on whether the cement void can provide a sufficient area for stress release. Perforations provide artificial stress release areas and reduce the casing stress, in spite of local stress concentration near the perforation points. The findings obtained herein provide a new understanding of the casing deformations in the Weirong shale gas field, and provide practical solutions to suppress casing deformation. • Casing deformation characteristics of shale wells in Weirong shale gas field were analyzed. • The mechanism of shale swelling-induced casing deformation was investigated. • Casing stress increases with the increase in shale swelling. • Swelling formation distribution affects the type of casing deformation. • Countermeasures to suppress the casing deformation were discussed.

Simulation of contact interface between elastic solids using smoothed particle hydrodynamics

In recent years, the use of the smoothed particle hydrodynamics (SPH) method has increased. However, most researches have restricted the application of this method to the fluids field. Few publications have reported the use of SPH to study solid problems. Moreover, only a small amount of investigations have considered the interface when two solids are in contact. The standard SPH method is able to determine the interaction of two objects through mutual search of particles at the interface. Taking this into account, herein we report a new strategy named interfacial SPH for simulating the contact of elastic objects. In our simulations, the search domain only contained the particles of the object, and the interaction between the two objects was achieved by means of the interface force. First, the collision of two aluminium rectangles was simulated in order to test the usefulness of the simulation strategy at the linear interface. Later, the collision between two discs was simulated to test the strategy at the curved interface. Subsequently, the collision of two elastic rubber rings and the impact of a bullet on an elastic plate were simulated. These last two models showed how the strategy used in the present investigation can be applied for the simulation of large deformation of elastomers. Finally, this paper analysed the problems of applying the standard SPH method in the simulation of the interface contact between two solids. The XSPH method and the artificial stress method were used in our simulations to ensure simulation stability.

The synthesis and the antioxidant activity of 1-phenoxymethyl-4-aryl-5,6,7,8-tetrahydro-2a,4a,8a-triazacyclopenta[cd]azulene-3-carboxylic (or carbothionic) acid derivatives

New 1-phenoxymethyl-4-aryl-5,6,7,8-tetrahydro-2а,4a,8a-triazacyclopenta[cd]azulene-3-carboxylic (or carbothionic) acid derivatives have been designed, synthesized and evaluated for their in vitro antioxidant activity under conditions of the artificial oxidative stress using ionol, ascorbic acid and α-tocopherol as the reference drugs. It has been found that 1-phenoxymethyl-4-aryl-5,6,7,8-tetrahydro-2а,4a,8a-triazacyclopenta[cd]azulene-3-carbothionic acid derivatives 9b, 9c, 9d, 9e, 9f, 9i and 1-phenoxymethyl-4-(41-chlorophenyl)-5,6,7,8-tetrahydro-2,2a,8-triazacyclopenta[cd]azulene-3-carboxylic acid phenylamide 10 reveal a high antioxidant activity and a good in silico pharmacokinetic profile. The data obtained allowed us to select the most promising objects from the substances synthesized for further pharmacological screening for the presence of the antioxidant activity in vivo.

Rhyming Techniques and Identity in Korean Hip Hop

This article examines the development of Korean rhyming techniques by musically analysing phonetic and grammatical structure in Korean rap. Due to major differences between Korean and English, Korean MCs had to redefine what constitutes “rhyme” in Korean rap, and the conflicting definitions of what it means to rhyme in Korean reflect diverse identities in the Korean hip hop community. Through my musical analyses, I present five types of Korean rhyming techniques: flexible word order, artificial stress accents or artificial pitch accents, rhythmic motives, multisyllabic internal rhymes and translingual rhymes. I close the article by suggesting that there is an inevitable hybridity in Korean hip hop and socioeconomic class struggles that persists in Korea.

Preface

Thanks for your passionate involvements and professional supports to 2020 2nd International Conference on Computer, Communications and Mechatronics Engineering (CCME2020), which was held to carry out new attempts in Computer, Communications and Mechatronics Engineering fields through related academic researches and practical actions based on future directions. And special thanks also to all and Technical Program Committees and reviewers for their professional works and selfless giving of their precious time.CCME2020 was held via Tencent Online meeting on December 20, 2020 to avoid offline contact and inconvenience caused by traffic restriction against the backdrop of the current normalized the epidemic. While improving the research motivation and academic literacy of all participants, CCME2020 will more strengthen safety protection, actively respond to the current epidemic prevention and cooperate with the normalization of epidemic situation.In order to ensure the normal running of CCME2020 online meeting, our staff preset the test room in advance for participants for their testing on the connection of relevant equipment and the stability of normal operation. We also arrange dedicated staff to provide the authors with questions and guidance. CCME2020 online meeting was held normally with supports of Prof. Gaurang S Patkar, Prof. Manik Sharma and all attendees. Prof. Gaurang S Patkar from Don Bosco College of Engineering, India made keynote speech about Automated Grading of Oil Palm Fruits using Soft Computing, and Prof. Manik Sharma from DAV University, India shared his viewpoints on Design of Artificial Intelligent Stress Diagnostic System using Machine Learning, Soft Computing and Context Aware Computing Techniques.With professional assistances from Technical Program Committee on paper reviewing and checking, CCME2020 selected 44 paper contributions among 105 paper submissions covering Computer, Communications and Mechatronics Engineering eventually. All these selected papers have been reviewed by 2-3 reviewers and editors who major in relevant research areas and be detected instances of overlapping and similar text in submitted manuscripts via iThenticate software before submitting for publication in Journal of Physics: Conference Series.In terms of the main topics and subject areas involved in all selected submissions, and professional, rigorous and meticulous guidance from the reviewer, CCME2020 Conference Proceeding mainly cover Computer Technology, Image Recognition, Communication, Intelligent Information and Electronic Engineering.Sincerely hope for future cooperation with these rigorous and responsible reviewers, Technical program Committee, these authors with a high enthusiasm for academic research, and accurate and efficient publication of IOP Publisher. Thanks again for your active participation and contributions!CCME2020 Organization Committees

Characterization of Agronomical and Quality Traits of Winter Wheat (Triticum aestivum L.) for Fusarium Head Blight Pressure in Different Environments

For food security, it is essential to identify stable, high-yielding wheat varieties with lower disease severity. This is particularly important due to climate change, which results in pressure due to the increasing occurrence of Fusarium head blight (FHB). The objective of this study was to evaluate the stability of winter wheat (Triticum aestivum L.) grain yield under different environmental conditions. Twenty-five winter wheat varieties were evaluated under two treatments (naturally-disease infected (T1) and FHB artificial stress (T2)) during two growing seasons (2018–2019 to 2019–2020) in Osijek and in 2019–2020 in Tovarnik. The interaction between varieties and different environments for grain yield was described using the additive main-effects and multiplicative interaction (AMMI) effects model. The Kraljica and Fifi varieties were located near the origin of the biplot, thus indicating non-sensitivity to different environmental conditions. Principal component analysis (PCA) was used to understand the trait and environmental relationships. PC1 alone contributed 42.5% of the total variation, which was mainly due to grain yield, 1000 kernel weight and test weight in that respective order. PC2 contributed 21.1% of the total variation mainly through the total sedimentation value, test weight, wet gluten and protein content ratio (VG/P) and wet gluten content, in descending order.

Protective action of priming agents on Urochloa brizantha seeds under water restriction and salinity conditions

Abstract: Analyses of germination of seeds under artificial stress conditions are tools for a better understanding of the survival and adaptation capacity of species under natural stress conditions. Therefore, the aim of this study was to evaluate the effect of priming on seed germination, on breaking of dormancy, and on the length of Urochloa brizantha seedlings under water restriction and salt stress conditions. A completely randomized experimental design was used with four replications in a 3 × 6 factorial arrangement consisting of 3 germination conditions (water, water restriction with PEG, and salinity with NaCl) and 6 treatments [five priming solutions (distilled water, potassium nitrate, spermidine, gibberellin, and sodium nitroprusside) and a control (unprimed seeds)]. The following determinations were made: seed moisture content after priming (before drying) and after drying the seeds, germination test at seven and twenty-one days after sowing, germination speed index, viability by the tetrazolium test of the seeds remaining from the germination test, and seedling length. Priming is effective in minimizing the negative effects of water restriction and salinity. Use of sodium nitroprusside as a priming solution results in a lower percentage of dormant seeds and greater germination, vigor, and plant development.

Critical period for seed number determination in soybean as determined by crop growth rate, duration, and dry matter accumulation

• We used two independent approaches to identify the beginning and end of the critical period for seed number determination in soybean. • Critical period for seed number determination occurs during the R3-R6 phase. • Seed number was related to biomass accumulation during the critical period. • Accumulated biomass is a better predictor of seed number than crop growth rate or duration alone. Seed number (SN) is positively associated with aboveground dry matter (ADM) accumulation in most crop species. In soybean, there are discrepancies among studies relative to the start and end of the critical period for seed number determination. The objective of this study was to more precisely identify those two stages. To do so, we followed two approaches: (i) analyses of experimental data where differences in SN occurred as a result of variation in crop growth due to weather and management practices and (ii) review of published experiments where soybean was subjected to artificial stresses during specific crop phases. Following the first approach, we analyzed the relationships between SN versus ADM accumulation and its components, crop growth rate (CGR) and duration, for different reproductive phases using data from experiments that portrayed a wide range of environments and management practices. In the second approach, we compared SN values in stressed versus non-stressed treatments. Accumulated ADM during the R3 to R6 phase explained ca. 70 % of the variation in SN across experiments. The CGR during R3-R6 was also a good predictor of SN, but it had lower explanatory power compared with accumulated ADM, because CGR did not account for changes in duration of critical period across experiments. Review of published data, wherein soybean crops were subjected to artificial stresses during different reproductive phases, confirmed that the R3-R6 phase is a critical phase for SN determination in soybean. Key findings of this study were: (i) critical period for SN determination in soybean occurs during the R3-R6 phase and (ii) accumulated ADM during the critical period is a better predictor of SN compared with CGR because it accounts for differences in the duration of the critical period as a result of weather and management.

Effects of tubing degradation and pump position on extracorporeal circulation performance.

Extracorporeal circulation (ECC) is an integral part of cardiac surgery. Yet, the contact with artificial surfaces, mechanical stress, shear, and suction forces within the ECC pose a pronounced risk for damaging the corpuscular components of the blood. These suction forces may be reduced by a repositioning of the roller pumps employed below the reservoir. Furthermore, the repeated compression of the involved silicone tubing is likely to cause degradation. We present our observations regarding changes in the ECC performance following this degradation process. In vitro experiments were performed in a standard as well as a simplified ECC setup and included measurements of pressure, effective flow, and tubing restoring force over a time frame of 12hours with two different pump positions utilizing transit time flow measurement. Suction forces within the tubing could be significantly reduced by shifting the pump position below the reservoir. Regardless of the setup, the tubing showed significant loss of restoring force as well as effective flow over time. A shift of the pump position within the ECC setup can be recommended to prevent blood damaging negative pressures. Further research is necessary to evaluate the exact cause of the reduction of restoring force overtime as well as its risks for the patients. Finally, our results underline the importance of transit time flow measurements to collect reliable flow data.

Artificial papillary muscle device for off-pump transapical mitral valve repair

ObjectiveNew transapical minimally invasive artificial chordae implantation devices are a promising alternative to traditional open-heart repair, with the potential for decreased postoperative morbidity and reduced recovery time. However, these devices can place increased stress on the artificial chordae. We designed an artificial papillary muscle to alleviate artificial chordae stresses and thus increase repair durability. MethodsThe artificial papillary muscle device is a narrow elastic column with an inner core that can be implanted during the minimally invasive transapical procedure via the same ventricular incision site. The device was 3-dimensionally printed in biocompatible silicone for this study. To test efficacy, porcine mitral valves (n = 6) were mounted in a heart simulator, and isolated regurgitation was induced. Each valve was repaired with a polytetrafluoroethylene suture with apical anchoring followed by artificial papillary muscle anchoring. In each case, a high-resolution Fiber Bragg Grating sensor recorded forces on the suture. ResultsHemodynamic data confirmed that both repairs—with and without the artificial papillary muscle device—were successful in eliminating mitral regurgitation. Both the peak artificial chordae force and the rate of change of force at the onset of systole were significantly lower with the device compared with apical anchoring without the device (P < .001 and P < .001, respectively). ConclusionsOur novel artificial papillary muscle could integrate with minimally invasive repairs to shorten the artificial chordae and behave as an elastic damper, thus reducing sharp increases in force. With our device, we have the potential to improve the durability of off-pump transapical mitral valve repair procedures.

Experimental and computational analysis of structure-property relationship in carbon fiber reinforced polymer composites fabricated by selective laser sintering

A fundamental understanding of structure-property relationship of carbon fiber reinforced polymer (CFRP) composites fabricated by selective laser sintering (SLS) is essential to provide guidance to improve the mechanical properties in this promising additive manufacturing process. In the present study, we propose a new computational framework to evaluate the mechanical behavior of SLSed CFRP based on the representative volume element (RVE) model. Firstly, a new voxel-based fiber packing algorithm is proposed with the three-dimensional fiber orientation tensor to describe the fiber distribution. The porosity generated in the manufacturing process is also considered by adding spherical voids in the matrix region. In order to remove the artificial stress concentration induced by the voxel-based algorithm, a python script is developed to regenerate the geometries of different phases with conforming mesh. Meanwhile, the constitutive models of different phases in SLSed CFRP, i.e., matrix, fiber and interface, are established according to the material characteristics. Next, the proposed computational framework of SLSed CFRP is validated by the X-ray computed tomography (XCT) measurements and tensile tests of a representative SLSed carbon fiber/polyamide 12 (CF/PA12) composite. The effects of fiber volume fraction and fiber orientation distribution on the mechanical behavior of SLSed CF/PA12 composite are further quantitatively explored and ranked with regards to their influence on stiffness and failure strength.

Heat Treatment Response of Selectively Laser Melted AlSi10Mg

Abstract The age-hardenable cast alloy AlSi10Mg is the most widely used alloy for additive manufacturing of aluminium components by means of selective laser melting. Due to the rapid solidification, the material exhibits a fine cellular microstructure, composed of a supersaturated Al-matrix and a network of silicon along the cell boundaries. The temperature of the building platform as well as the built time both have an influence on the level of precipitation in the material and this in turn affects the heat treatment response of AlSi10Mg in as-built condition. Material built on a cold platform can be strengthened by direct artificial ageing and shows only a small loss in strength after a stress relief heat treatment. Material built on a preheated platform has the highest strength in as-built condition and subsequent artificial ageing or stress relieving causes softening of the material. A condition which is truly independent of the platform temperature can only be reached by applying a solution heat treatment followed by quenching. Unlike castings, which need a long-term solution heat treatment to reach optimum mechanical properties, the selectively laser melted material shows the best mechanical properties in T6-condition after a solution heat treatment of short duration