bluuebunny/crossref_metadata_2025 huggingface dataset:
Research on the Application of Financial Non-performing Assets Appraisal Based on Comprehensive Factor Analysis Method
Authors: Xiao Nanyun , Xu Yan , Duan Hongcheng
Published: September 2021

The wanton growth of non-performing financial assets is fatal to the entire financial industry. Based on the research background, significance and content of financial non-performing assets, this paper first expounds the concept, classification and formation reasons of financial non-performing assets; secondly, it enumerates the common methods of financial non-performing assets appraisal in China; then, the method is applied to an actual case; finally, this paper analyzes the application of the method in the evaluation of non-performing financial assets, and summarizes the full text. The research shows that: when the problems of incomplete debtor information, complex causes, involving a large number of related parties and related assets make it difficult to carry out the evaluation work, the comprehensive factor analysis method provides more possibilities.
The Influence of terrorism on Foreign Direct Investment
Authors: Liu Ran , Ruan Wenjing , Qi Jipeng
Published: September 2021

In the process of globalization, the spread of terrorism has brought risks and uncertainties to multinational enterprises. In order to find out the influence of terrorism, this research use the Chinese multinational enterprises’(MNEs) 2089 investments in 125 countries to studies the impact of terrorist events on their investment decisions. The research find that the the more people affected by the terrorism in one country, the less subsidiaries set up in the countries. Terrorist events have brought severe challenges to investment. Governments of countries should improve their own security protection systems, while enterprises should also strengthen the risk management system.
Dynamic Analysis of Total Factor Productivity (TFP) of Traditional Chinese Medicine (TCM) Hospitals in Hubei Province from 2013 to 2019
Authors: Cheng Tang , Jun MA , Li Chen
Published: September 2021

Objectives: To study the changes of TFP in TCM hospitals in Hubei Province from 2013 to 2019, so as to provide policy basis for improving service efficiency and promoting the development of TCM. Methods: The statistical reports of 90 public TCM hospitals in Hubei Province from 2013 to 2019 were collected using the Hubei Provincial Comprehensive Statistical Information System for TCM, and the TFP of TCM hospitals were dynamically analysed using the DEA-Malmquist index method. Results: From 2013 to 2019, the Total Factor Productivity Change (TFPCH) index of TCM Hospitals in Hubei Province increased by 0.8%; the Efficiency Change (EFFCH) index increased by 0.5%; the Technical Change (TECH) index increased by 0.3%; the Pure Efficiency Change (PECH) index increased by 0.2% and the Scale Efficiency Change (SECH) index increased by 0.4%. The mean values of the TFPCH index in the eastern, central, and western regions of Hubei Province were 1.001, 1.011, and 1.013, respectively, and the mean values of that in the secondary and tertiary hospitals were 1.004 and 1.024, respectively. Conclusions: The TFP of TCM hospitals in Hubei Province tends to improve on the whole. There are differences in the TFPCH index of TCM hospitals in different regions and levels. The stage development characteristics of core cities play a leading role and are worth learning.
Exploring the Flexible Talent Introduction Mechanism for the Development of Airport industry in G City from the Perspective of Talent Governance
Authors: Luo Liangmei , Wang Xiaohui
Published: September 2021

Promoting flexible talent introduction is an important part of innovative talent governance, and an effective mechanism to promote the flow of talents and release the vitality of talents. As an airport industry relying on resources such as convenient transportation, advanced logistics and strong radiation effects from large-scale hub airports, its core resources are still human resources. It is a strategic choice for the rapid development of the airport industry to quickly tap and introduce talents and give full play to the advantages of talents. At present, the theoretical and practical circles still lack in-depth discussions on the flexible talent introduction mechanism of the airport industry. This research focuses on the problems and causes analysis of the flexible introduction of talents in the airport industry in G City, and tries to start from the three governance concepts of collaborative governance, dynamic governance and risk governance, and proposes innovations in the talent policy system that promotes flexible introduction of talents, and innovations in talent introduction methods. Flexible introduction of countermeasures and suggestions for risk aversion. Hope to promote the in-depth study of the flexible talent introduction model.
Research on the Influence of Government Regulation on Green Technological Innovation of Strategic Emerging Industry
Authors: Gao Jing , Feng Qiuhong , Zhan Wanfei
Published: September 2021

In the green economy, strategic emerging industries to implement Class II green technological innovation keep critical to obtain competitive advantages. The government regulation could effectively make up for the shortcomings of the negative externalities of green technological innovation. In order to further explore the impact of government regulation on Class I, II and III green technological innovation of strategic emerging industries, this article utilizes the strategic emerging industries as the main experimental subject. Through constructing a tripartite evolutionary game model of strategic emerging industries, the government and consumers, it reveals the process of the three-party discretionary selection in the process of green technology innovation, and acquires equilibrium strategies of the tripartite in the process of green technological innovation.
Study on Government Functions in Privatization of Public Stadiums- Based on Effective Supply of Double-level System
Authors: Yang Fenghua
Published: September 2021

In the two-level system of effective supply of public stadiums, institutional supply is the constraint of product supply, and product supply feeds back to the formation of institutional supply. The establishment and change of the government function supply system is the key to the efficiency of privatized product supply. Therefore, the government in the process of privatization of public stadiums and gymnasiums in our country will realize the corresponding and complete regulatory functions before entering, during access, during implementation and after exit.
The Construction Path of University Smart Libraries Facing Strategic Emerging Industries
Authors: nan Xiao nan
Published: September 2021

The development of strategic emerging industries is inseparable from the support and guarantee of information resources. The multiplier effect of information resources can enhance the industry’s independent innovation and international competitiveness. Under the background of the all-round development of strategic emerging industries and the acceleration of the construction of emerging professional disciplines in universities, the intelligent construction of university libraries is an inevitable choice. This article aims to analyze the necessity of intelligent construction of academic libraries for strategic emerging industries, build a new system model of intelligent intelligent libraries in universities, propose cultivating intelligent groups to improve intelligent literacy, and use intelligent technology to tap new kinetic energy of university libraries. Strengthen the construction path of new ways of space management innovation and development of smart cities.
The evolutionary characteristics of the network attention of the five tourism performing arts products on the time scale
Authors: Guanghong Li , Yulin Zhang
Published: September 2021

Network attention is the intuitive expression of tourism demand and behavior habits on the Internet, with the help of Baidu Index platform to obtain the online attention of the five major tourism performing arts products from 2015 to 2019, and use quantitative methods to analyze their annual, monthly and weekly changes. The results are as follows, from the perspective of interannual change, the network attention of “Ancient Love of Song City” and “Amazing Xiangxi” shows an upward trend, while the rest of the impression series products show negative growth; from the perspective of monthly change, the network attention of “Impression Liu Sanjie", “Ancient Love of Song City” and “Impression West Lake” has seasonal characteristics; the overall change trend is mainly affected by the National Day holiday and summer vacation, the curve trend of “Impression Lijiang” and “Amazing Xiangxi” is relatively stable; from the weekly change, the weekly change of tourism performing arts products is very small.
The influence of spatial distribution of producer services on high quality development of manufacturing industry
Authors: Chen LiXian , Cai XinMing , Zou KaiZhang
Published: September 2021

Based on the provincial data of China from 2004 to 2018, this paper empirically tests the impact of the spatial distribution of producer services on the high-quality development of manufacturing. It is found that the spatial distribution of producer services significantly promotes the high-quality development of manufacturing, and there is no heterogeneity of geographical location and economic development level.
On the Strategy of Shaping Rural Human Settlement Environment in Jiangsu Province from the Perspective of Beautiful Pastoral Country
Authors: Xinguo Yuan , Xingping Wang
Published: September 2021

Beautiful pastoral country construction is an important step for Jiangsu Province to fulfil the mission of “being a leader, a model and a front-runner” in rural revitalization, and it has become an important part of realizing the beautiful province of Jiangsu. By means of data comparison, literature analysis and logical analysis, it is possible to outline the current characteristics of unbalanced regional development, uneven distribution of characteristic resources and mismatch of the “agriculture, rural areas and farmers” policies with the new development requirements in the province, and by referring to the model of rural revitalization in the “six along” areas, systematic thinking and planning of “agriculture, rural areas and farmers” policies and other strategies, with focus on the systematic construction of agriculture, rural areas and farmers, is helpful to improve the habitat environment in Jiangsu in all respects. The results show that the strategy of building beautiful pastoral country in northern, central and southern Jiangsu should be adapted to local conditions; Jiangsu should take the lead in the construction of beautiful pastoral country in the “six along” areas; the key to the construction of beautiful pastoral country lies in the industrial development in rural areas. The two should be closely coordinated and driven by each other to jointly achieve the modernization of agriculture and rural areas.
The Impact of Foreign Trade on China’s Industrial Transformation and Upgrading
Authors: Chen Jun
Published: September 2021

In the context of the continuous opening up of China’s foreign economic development, the coordinated development of foreign trade and industrial transformation and upgrading has always been a hot issue in industrial economics and international trade research. Through empirical analysis to study the impact of foreign trade on industrial transformation and upgrading, this paper finds that there is a long-term dynamic synergy relationship between foreign trade and industrial transformation and upgrading. At the same time, this article also finds that the export value of goods trade and the import value of service trade have a significant impact on industrial transformation and upgrading, while the import value of goods trade and the export value of service trade have no significant impact on the industrial transformation and upgrading. Finally, this article puts forward policy recommendations on the promotion of industrial transformation and upgrading by foreign trade on this basis, so as to provide references for industrial policy makers.
Analysis of econometric research hotspots and application prospects —— visualization research based on citespace
Authors: Sun Xiaolin , Zhao Menghe
Published: September 2021

By analyzing scholars’ research on econometrics, we can understand the hot topics of related research and, based on the changes of research hotspots in different years, we can derive the future application prospects. In this paper, the literature related to econometrics in cnki and web of science is selected as the sample source, and the literature between 2010 and 2020 is analyzed by the visualization software citespace for authors, keywords, etc. Through the study, it is found that the application of spatial econometrics and the solution to practical problems are the focus of current scholars’ research, and the application of econometrics is very wide, and the solution to practical problems is the new trend of econometric research in the future.
Analysis on the influencing factors of industrial structure upgrading in Northeast China
Authors: Dong Dapeng , Xu Yan , Zhao Guiyan , Qi Yihui
Published: September 2021

Based on the panel data of 34 cities in Northeast China, this paper uses fixed-effect model and quantile regression method to empirically test the influencing factors of industrial structure upgrading. The results show that the government has led the upgrading of the industrial structure in Northeast China, economic growth and investment in fixed assets has inhibitory effect on industrial structure upgrade, the level of opening to the outside world, the financial sector development and the increase of human capital in the northeast has obvious role in promoting industrial structure upgrade. The quantile regression results show that the coefficient of each factor are basically consistent with the estimated results of ordinary panel fixed effect model, which further verifies the robustness of the research conclusions in this paper.
The Construction of WTO Framework for the Development of My Country’s Information Technology Sports Industry Based on Big Data
Authors: Yuezhong Li , Yichong Liu
Published: September 2021

With the improvement of China’s economic level and the level of science and technology, people’s demand for sports products and services is greatly increasing, and China’s sports industry is showing a trend of diversified development. This article discusses the characteristics and connotations of the traditional sports industry and the characteristics of the sports industry in the era of big data, and then points out the challenges faced by the sports industry under the WTO framework and makes relevant recommendations. This paper also investigates the development status of the sports culture industry in our city through experiments, and the results show that the sports culture industry in our city involves 12 categories, of which sports film and television industry accounts for only 14.3%.
Discussion on Tourism Industry Trend under Routine Prevention and Control of Epidemic
Authors: Li Pei
Published: September 2021

The tourism industry is still in the recovery period after experiencing the suspension caused by the COVID-19 epidemic. At present, it seems that the epidemic prevention and control has become a routine job, in this context, some changes and new trends are taking place to the tourism industry. This paper analyzes the data based on the tourism market and discusses the major trends in the development of the tourism industry. The analysis reveals that the consumer appetite to travel was not blunted by COVID-19 even if many countries and regions are currently closed for tourists. Health and safety continue to be main concerns of tourists during their travels. In addition, there is a growing tendency toward industrial integration as the tourism demand is becoming increasingly diversified and personalized. Another definite trend in the tourism industry is the digitalization construction in tourist destinations. It is certain that the digital technology will provide travel businesses with more possibilities, and the tourism industry, guided by the innovation-driven development strategy, will have a promising future.
Research on the Innovation of Cross-border E-commerce Customer Service Model Based on Big Data in the Post-epidemic Era
Authors: Liang Jiahui
Published: September 2021

In the post-epidemic era, with the rapid development of cross-border e-commerce, massive amounts of customer information data are generated every day. This article explores useful business information data, innovates cross-border e-commerce customer service model, optimizes customer service details, meets customer needs, and creates greater profits for the company. This article defines big data, expounds the 5V characteristics of big data and commonly used analysis methods, analyzes the positive impact of big data on cross-border e-commerce customer service, and the problems of big data application in cross-border e-commerce customer service, and proposes targeted cross-border innovations Countermeasures for e-commerce customer service model.
Interpretation of Economic Growth and Water Pollution Intsity Based on EKC model
Authors: Qiang Li , Jianmin Huang , Wenrui Wang , Xuerong Wang
Published: September 2021

Based on the extended Environmental Kuznets model (EKC) and the spatial econometric method, this paper analyzes the emission intensity data of water pollution of Chinese provinces and cities from 2004 to 2018 to identify the key factors that could result in water pollution by different periods of time and by different regions as well as to initiate discussions over potential policies to be taken in the future. The results have two implications: on the one hand, water pollution is highly spatially correlated among different Chinese regions and the economic growth indicators such as GDP per capita and the number of lights show an inverted U-shaped nonlinear relationship with the intensity of water pollution emissions. As water pollution demonstrates both leakage effect and spillover effect, it is important to strengthen the implementation strategy featuring comprehensive planning and joint prevention and control. This paper also locates the performance of each region on the EKC curve. As demonstrated in the results, Shanghai, Beijing and Tianjin have become the first ones to manage to cross the inflection point and maintain at this level. Zhejiang, Jiangsu, Shandong and other eastern coastal areas are situated in the peak of the EKC curve, with enormous emission reduction pressure. Most of the provinces in the central region are located at the left side of the peak, and are suffering from serious water pollution resulted from rapid economic growth. Meanwhile, the intensity of water pollution in the western region of China is increasing rapidly. It is integral to seize the opportunity of supply-side reform to speed up the industrial restructuring, and try not to repeat the old lesson of treatment after pollution. In conclusion, it is suggested that governments at all levels should formulate and customize their policies based on their location on the EKC curve, so as to achieve positive dynamics between economic growth and water pollution control.
FDI, Spillover Effect and Green Total Factor Productivity (GTFP) - Research from the Perspective of Regional Heterogeneity
Authors: Xiao Hang , Zhang Xiangjian
Published: September 2021

The report of the 19th National Congress of the Communist Party of China emphasized the need to promote green development and strengthen the environmental protection system. China’s introduction of foreign investment has gradually shifted from emphasis on “quantity” to “quality” in the context of the new normal. In view of this, this paper discussed the mechanism of impact of FDI on China’s regional GTFP with the relationship between FDI and the regional GTFP as the logic starting point. The research results show that FDI has in general exerted a “pollution halo” effect in China, which affects the regional GTFP through technology and human capital spillover effects; FDI has non-linear impact on GTFP at different levels of environmental regulation and marketization; “pollution haven", “bottom line competition” and other phenomena will occur at low levels of environmental regulation and marketization; FDI will inhibit the increase in China’s regional GTFP; the impact of FDI on GTFP is regionally different, and the western and northeastern regions are “pollution havens” in China.
Genetic and environment factors of mental disorders: Twin studies about Alzheimer’s disease, Phobia and Autism Spectrum Disorder
Authors: Wei Siyang , Xin Zilan , Zhang Yuankai
Published: September 2021

With the natural and social environment changing, people’s mental health is facing severe challenges. Many people are suffering from mental disorders in the present day. A large part of mental disorders can be linked with the nerve system. And nerve system disorders tend to be associated with the development of nerve systems. The gene and the environment can play an important role in the development of the body, and abnormal genes and detrimental environmental factors can contribute a lot to nerve system disorders. Previous research has studied the occurrence and gene-and-environmental impact of many nerve system disorders. Among them, this essay chooses three kinds of disorders: Alzheimer’s disease (AD), Phobia, and Autism Spectrum Disorder, which can cause a lot of trouble in people’s daily life. In this essay, we are to study the occurrence of some nerve systems’ disorders and hope to study the genetic and environmental contribution of these disorders. These three disorders gain a lot of attention as they are very common, and they can partly reflect the contribution of genes and the environment.
A Progress on the Application of Tetrodotoxin
Authors: Wang Zhaojia , Zhou Zhenning
Published: September 2021

Tetrodotoxin (TTX), a blocker of sodium channels, exists in the pufferfish, amphibians, and octopus, and originated in endosymbiont-vibrio. Researches have confirmed that TTX affected the action potential through the regulation of voltage-gated sodium channels (VGSCs) and the ingestion of TTX inhibits the nerve signal’s transmission, showing symptoms like rapid weakening and paralysis of the muscles. Recent research shows that TTX’s medical value as the analgesic is mainly focused. The comparison on efficacy among placebo, TTX, and opioids manifests that TTX is healthy and effective in treating neuropathic pain. Moreover, since the drug is synthesized by TTX, it can block specific neurons to alleviate the pain on different parts of the body accurately. Currently speaking, TTX has been widely used as medicine for the alleviation of cancer pain. The mechanism, symptoms, application, and treatment are thoroughly discussed to popularize TTX and pass the “torch” to the new generation because there is still a long way to go—the unsolved mysteries of TTX awaiting humans.
Statistical Investigation of Correlation between Cardiovascular Event ad Hypertension
Authors: Dai Linfei , Song Mingyang , Zhang Danni
Published: September 2021

Cardiovascular disease is one of the most severe health killers in modern life. In this study, the association among the risk of cardiovascular diseases, patients’ blood pressure and treatment was analyzed. This study makes a secondary analysis on the data from the Evidence for Cardiovascular Prevention from Observational Cohorts in Japan (EPOCH-JAPAN) database. Participants have recruited 39705 representative participants with diverse blood pressure. The results show that the treated participants have a higher proportion of diabetes mellitus, dyslipidemia, and history of cardiovascular diseases (P<0.0001), compared with untreated participants. During the 10-year follow-up period, there were 2032 cardiovascular deaths distributed among coronary heart disease(CHD), heart failure, and stroke. The treated participants showed an significantly risk for cardiovascular mortality (Hazard ratios (HR):1.5; 95% confidence intervals (CI):1.36-1.66), CHD (HR:1.53, 95%CI: 1.23-1.9), heart failure (HR:1.39; 95%CI: 1.09-1.76) and stroke (HR:1.48; 95%CI: 1.28-1.72). Especially for the participants under antihypertensive medication, their risk of cardiovascular mortality was 1.5 times higher than that of the untreated participants.
Effect of obesity on several types of cancer
Authors: Zhao Yushi , Yang Tianyi
Published: September 2021

Currently, both trends of obesity and awareness of the possible adverse effects of obesity are rising in our population. According to the World Health Organization, about one third of the world's population is suffering from obesity-related health problems. Cancer, a severe progressive disease that is becoming more and more common, is among them. However, the association between obesity and cancer is not informed very well by the public. In this paper, the first part will briefly introduce present situations of obesity and common complications of obesity. The following two parts will explain the mechanisms of cancer formation and discuss the relationship between obesity and cancer in an understandable way.
Effects of different extractions on growth and nutritional quality of hydroponic endivia
Authors: Li Chunyan , Mo Jianchao , Liu Yuhang , Zhang Ruijie , Wang Haixia , Su Lihong , He Zhongqun
Published: September 2021

In this study, Hydroponic endivia with completely decomposed distiller’s grains, tea residue and extraction of commercial organic manure were applied to study its effects on growth and nutritional quality of endivia, as compared with modified Hoagland nutrient. The results showed that the root-shoot ratio of endivia under all treatment conditions was higher than that in CK group. Among them, treatment Ⅳ exhibited best improve efficiency; the treatment of Ⅰ, Ⅱ, Ⅴ, Ⅵ were beneficial to reduce the nitrate content. The treatment Ⅰ significantly increased the content of VC and soluble sugar. The soluble protein content of treatment Ⅴ was the highest. Above all, the application of tea residue and commercial organic fertilizer extracts in the actual production of hydroponic lettuce needs further and deeper research.
The Actual Cause of Gender Difference after Coronary Artery Bypass Grafting
Authors: Suo Zihan , Yang Yuxuan , Zhang Jianing
Published: September 2021

Cronary Artery Bypass Grafting (CABG) surgery is a widely practiced procedure among treatments of coronary heart disease. While being able to significantly prolong the life of patients, it is a high-risk procedure characterized by a relatively high 30-day postoperative mortality. The risk and benefits of this procedure have made it to be a focus of research in recent years. Thereinto, research was dedicated to exploring postoperative short-term mortality rate, which is affected by various factors including gender. Based on statistics, a clear pattern is demonstrated that the mortality of women is significantly greater than men. Furthermore, various confounding factors are involved, including preoperative status, physiological difference, and susceptibility for complications. By taking these factors into account, this review aims at establishing the actual cause of gender difference in short-term mortality after CABG. Besides, feasible approaches to lower the overall mortality are proposed, especially by targeting factors that led to the elevated mortality in women. These results will offer a guideline for CABG treatment.
Initial Characterization and Expression Pattern Analysis of Tobacco (Nicotiana Tabacum) Sucrose Synthase Gene
Authors: Zhao Meiwei , Zou Juan , Leng Sixuan , Tao Ying , Zhao Zhengxiong
Published: September 2021

A novel tobacco(nicotiana tabacum) sucrose synthase genewas characterized using the rapid amplification of cDNA ends methods based on one tobacco EST. Thissucrose synthase gene mRNA was 2,954bp in length containing a 2,418bp open reading framewhich encodes a protein of 805 amino acids. Sequence analysis revealed that thissucrose synthase of tobacco shares high homology with the sucrose synthase of Nicotianaattenuata(98%), Nicotianasylvestris(98%), Nicotianatomentosiformis(98%), Capsicumannuum(95%), Capsicumbaccatum(95%), Solanumtuberosum(94%), Solanumlycopersicum(94%) and Solanumpennellii(94%). Results also showed that tobacco sucrose synthase gene has a closer genetic relationship with the sucrose synthase gene of Capsicumannuum.Genomic DNA analysis indicated that tobacco sucrose synthase gene is structured in 13 exons and 12 introns.Tissue expression profile analysis revealed that this tobacco sucrose synthase gene was highly expressed in leaf, but moderately expressed in root, stemand flower. These established the foundation for further research on the tobacco sucrose synthase gene.
Changes of retinal thickness in macular area of myopia children
Authors: Meihong Zhu , Tainan Lin
Published: September 2021

Objective: To study the changes of macular retinal thickness in children with moderate and low myopia by frequency domain OCT. Methods: 108 school-age children aged 7-12 years were selected and enrolled into the group. Among them, 58 cases (116 eyes) with simple moderate and low myopia in the myopia group and 50 cases (100 eyes) with straight eyes in the emmetropia group. The retinal thickness in different parts of macular area was compared between the two groups, and the correlation between retinal thickness in different parts of macular area and diopter and axial length was analyzed by Pearson correlation analysis. Results: The length of eye axis in moderate and low myopia group was longer than that in emmetropia group, and the difference was statistically significant (P < 0.05). There was no significant difference in CMT(Central Macular Thickness) and I-AMT(average macular thickness of inner circle) between the two groups (P > 0.05). The AMT(Average Macular Thickness) and O-AMT(average macular thickness of outer circle) in moderate and low myopia group were lower than those in emmetropia group, and the differences were all statistically significant (P < 0.05). The thickness of the retina below the macula and the nasal side was positively correlated with the refractive power in patients with moderate to low-grade myopia (r=0.201, 0.302, P＜0.05), and the thickness of the retina around the macula was negatively correlated with the refractive power (r=-0.326, P＜0.05). Conclusion: There is no significant difference in macular central retinal thickness between children with moderate and low myopia and normal children, and the thickness of paracentral retina tends to become thinner with the deepening of myopia.
Extending the annular in-plane torsional shear test specimen to applications at high strain rates
Authors: Osman Muhsin , Cloete Trevor John , Ismail Ernesto Bram
Published: September 2021

In-plane torsional shear testing is a well-established material testing technique in the metal forming community. The corresponding specimen is designed to be machined from sheet metal with a continuous annular shear zone intended to deform in simple shear. Consequently, there are no geometric discontinuities or “edge-effects” to induce volumetric changes or instabilities with the result that large true plastic strains up to 1.0 can be achieved. This paper presents an extension of the in-plane torsional shear test to the dynamic regime. Dynamic experiments were performed using a torsional split Hopkinson bar (TSHB) on specimens manufactured from Al 1050 H14. The experimental results show that the adopted technique can be used to determine the material behavior accurately and reliably in the dynamic regime.
Simultaneous Full-Field Strain and Temperature Measurements in Tensile Hopkinson Bar Experiments at Extreme Temperatures
Authors: Soares Guilherme C. , Hokka Mikko
Published: September 2021

Simultaneous full-field strain and temperature measurements were used to monitor tension Split Hopkinson Pressure Bar (SHPB) tests at elevated temperatures. A direct heating system was used to increase the specimen temperature up to 1350 °C. Digital Image Correlation (DIC) and Infrared Thermography (IRT) were used was used to simultaneously monitor the evolution of the full-field strain and temperature of the specimen. Data acquisition was synchronized using a function generator, a camera pinhole model was used to represent both strain and temperature on the same coordinate system, and the displacement vector field from DIC was used to represent both datasets on the same reference frame. The use of fullfield techniques was essential at elevated temperatures, as necking occurred soon after yielding and the usability of the data obtained from the SHPB after the onset of necking is debatable. The method was able to follow the full-field strain and the temperature evolution under extreme conditions. Some challenges were found in the development of the method and recommendations as well as future applications are also described in this paper. This experimental approach is versatile and can be applied to different materials at similar testing conditions but also different loading modes and testing setups.
Evolution of dynamic shear strength of frictional interfaces during rapid normal stress variations
Authors: Rubino Vito , Tal Yuval , Rosakis Ares J. , Lapusta Nadia
Published: September 2021

Pressure shear plate impact tests have revealed that when normal stress changes rapidly enough, the frictional shear resistance is no longer proportional to the normal stress but rather evolves with slip gradually. Motivated by these findings, we focus on characterizing the dynamic shear strength of frictional interfaces subject to rapid variations in normal stress. To study this problem, we use laboratory experiments featuring dynamic shear cracks interacting with a free surface and resulting in pronounced and rapid normal stress variations. As dynamic cracks tend to propagate close to the wave speeds of the material, capturing their behavior poses the metrological challenge of resolving displacements on the order of microns over timescales microseconds. Here we present our novel approach to quantify the full-field behavior of dynamic shear ruptures and the evolution of friction during sudden variations in normal stress, based on ultrahighspeed photography (at 1-2 million frames/sec) combined with digital image correlation. Our measurements allow us to capture the evolution of dynamic shear cracks during these short transients and enable us to decode the nature of dynamic friction.
2D numerical simulation of auxetic metamaterials based on global DIC
Authors: Trippel Antonina , Gutmann Florian , Ganzenmüller Georg , Hiermaier Stefan
Published: September 2021

This work discusses a novel approach to simulate metallic auxetic structures manufactured via Selective Laser Melting (SLM). SLMmanufactured metamaterials are difficult to simulate accurately based on nominal geometry and bulk material behaviour. The geometry after printing is different from the nominal CAD geometry. Artefacts due to the printing process such as pores yield a material behaviour which depends on the surface/volume ratio. We investigate a phenomenological approach to obtain a simulation model calibrated with experimental data and Digital Image Correlation (DIC). Finite Element based global DIC as suggested by Hild [1,2] allows for obtaining accurate displacement fields, consistent with the true deformation of the lattice structure. Based on the nominal CAD geometry, a simplified parametrized simulation model is created, exploiting the abundant symmetries of lattice structures. Using nodal displacements from DIC in combination with the expected forces from an experiment, the model is calibrated via LS-OPT. The approach is applied to an antitetrachiral, auxetic structure. Furthermore, we discuss the accuracy of the approach, its applicability to other structures and possible extension into 3D space.
Evaluation of impact ductile fracture behaviour of low carbon austenitic stainless steel SUS304L using damage mechanics model
Authors: Takazawa Hidekazu , Yashirodai Kenji , Yamada Hiroyuki , Ogasawara Nagahisa , Kumagai Tomohisa
Published: September 2021

To clarify the applicability of the Gurson-Tvergaard-Needleman (GTN) model for impact ductile fracture behaviour, SHB test was reproduced by finite element analysis (FEA). The strain-rate dependence of the strength for austenitic stainless steel JIS SUS304L was obtained by tensile tests at quasi-static strain rate and impact strain rate. The CowperSymonds power law, which takes into the strain-rate dependence of strength, and the GTN model implemented in the commercial FEA code were used to simulate for impact ductile-fracture behaviour. GTN model parameters were determined by minimizing the difference between the simulated and measured stress-strain curve using response surface method. SHB test was simulated using GTN model obtained from quasi-static tensile test result. Simulation results did not occur the necking and fracture on the specimen. The fracture surfaces were observed by SEM micrograph. The appearance of ductile fracture since dimples are observed, regardless of the strain rate. It is necessary to adjust the parameter to accelerate the nucleation of the void. By identifying the GTN parameters in consideration of the strain rate dependence including impact strain rate. It would be possible to improve the simulation accuracy of impact ductile fracture behaviour.
Characterization of Ottawa Sand and Application to Blast Simulations
Authors: Chocron Sidney , Carpenter Alexander , Nicholls Arthur , Walker James , Elbaz Ohad , Rejovitzky Elisha
Published: September 2021

The present work aims at presenting consistent data both from laboratory characterization and from blast tests to see how a computer model performs when only data from mechanical tests are being fed to the constitutive model. A sand (Ottawa 20-30) that meets ASTM C778 requirements, i.e., well characterized microscopically, was tested in triaxial compression under confinement pressures ranging from 50 to 300 MPa and moisture contents of 0 to 15% as well as high strain-rates. These tests provided both the experimental equation of state (pressure vs. volume) and compaction curves as well as the strength vs. pressure properties to build a constitutive model both in LS-DYNA and CTH. Blast tests were subsequently performed by burying explosive at three different depths inside a sand pot with a rigid steel plate on top. During flight, the height of the steel plate was tracked with Phantom high-speed cameras to determine the impulse transmitted to the plate as well as the maximum jump height. Simulations were performed with both an Eulerian code (CTH) and a Lagrangian/ALE code (LS-DYNA) using the constitutive model determined during the material characterization. The predictions of both codes are as close as 7% and as far as 22%, depending on the test configuration.
Direct atomistic simulations of metastable state destruction in titanium (β-α martensitic transition) caused by external influences
Authors: Chirkov Pavel V. , Kichigin Roman M. , Karavaev Alexey V. , Dremov Vladimir V.
Published: September 2021

Large-scale classical molecular dynamics (CMD) is utilized to simulate the β→α phase transition in pure titanium. Samples with a metastable polycrystalline bcc structure are prepared using crystallization from liquid state and subsequent recrystallization at elevated temperatures. Controlling the heating-cooling regimes we prepared two different kinds of samples with coarse and fine grain structures. The metastable bcc samples were relaxed at temperatures noticeably lower than the equilibrium β-α transition temperature. During the following cooling of the samples down to room temperature, transitions to the α phase start. With the prepared metastable bcc samples of two kinds we perform the CMD study of the β→α transition under plain shock wave loading and imposed shear deformations. From the CMD simulations we obtain information about the transformation barriers, mechanisms, and kinetics. Results of CMD simulations suggest that grain boundaries hamper the hcp phase growth.
On the Temperature Dependent Mechanical Response of Dynamically-loaded Shear-dominated Adhesive Structures
Authors: Erice Borja , Lißner Maria , Wittig Jan , Hornig Andreas , Gude Maik , Petrinic Nik
Published: September 2021

A mode II mechanical characterisation of the adhesive joints is performed testing shear lap joint specimens in a Split Hopkinson Tensile Bar (SHTB), equipped with a temperature chamber. The experimentallyobtained traction-separation curves were used to develop a Cohesive Zone Model (CZM) capable of representing the strain-rate and temperaturedependent mechanical response of the adhesive joints. To validate the model, End Notch Flexure (ENF) multi-material specimens made from titanium and carbon fibre reinforced polymer composite laminates were tested at different temperatures using a Split Hopkinson Pressure Bar setup with an in-house made temperature chamber. The finite element (FE) simulations of such tests employing the developed CZM showed the model’s ability to accurately predict the adhesive joints’ failure as well as to understand the failure sequence of multi-material adhesive joint combinations.
Split Hopkinson bar tests on metaconcrete: modeling and numerical simulations
Authors: Briccola Deborah , Cadoni Ezio
Published: September 2021

The work deals with the dynamic characterization of metaconcrete, a mechanical metamaterial with locally resonant inclusions and unconventional dynamic performance. Metaconcrete can be defined as an unusual concrete in which standard aggregates are partially replaced by engineered ones made of a rigid heavy core covered by a compliant layer. From a mechanical point of view, its mitigation properties are associated to the mechanical energy trapped by the inclusions when acted upon by an elastic pulse with a frequency content close to their own resonant frequencies. So far, a discrete number of experimental investigations have been performed but none of these consider the impulsive nature of blast and impact loadings and the direction of the incoming wave with respect to the inclusion orientation in case of a brittle matrix. The results of numerical simulations considering different configurations of engineered inclusions within a single metaconcrete unit are compared in terms of stress level attained as well as internal and kinetic energy involved. Metaconcrete can bring about disruptive applications in several fields of applied sciences, but for the technology to become firmly established a synergism between computational and experimental approaches is paramount.
Crack arrest and propagation in impact loaded shock resistant PMMA: mesh-free numerical simulation
Authors: Tan Kean-Sheng , Longère Patrice , Mat-Jali Norazrina
Published: September 2021

The use of shock resistant RT-PMMA in engineering structures potentially subject to accidental overloading requires an evaluation of its crack arrest capability under impact loading. Based on experimental results obtained from a series of Kalthoff and Winkler (KW)-type impact tests, the present study aims at numerically reproducing the conditions for brittle-like crack initiation and propagation in impact-loaded RT-PMMA. For that purpose, three-dimensional SPH numerical simulations were conducted and the performance of various failure criteria was evaluated. The numerical model together with a combination of stress- and strain- dependent failure criteria were shown to fairly reproduce the experimental results in terms of finite crack advance and orientation.
Impact perforation of sandwich panels with graded hollow sphere cores: Numerical and Analytical investigations
Authors: Elnasri Ibrahim
Published: September 2021

In this study, we numerically and analytically investigate the impact perforation of sandwich panels made of 0.8 mm 2024-T3 aluminum alloy skin sheets and graded polymeric hollow sphere cores with four different gradient profiles. A suitable numerical model was conducted using the LS-DYNA code, calibrated with an inverse perforation test, instrumented with a Hopkinson bar, and validated using experimental data from the literature. Moreover, the effect of boundary conditions on the perforation resistance of the studied graded core sandwich panels was discussed. The simulation results showed that the piercing force– displacement response of the graded core sandwich panels is affected by the core density gradient profiles. Besides, the energy absorption capability can be effectively enhanced by modifying the arrangement of the core layers with un-clumping boundary conditions in the graded core sandwich panel, which is rather too hard to achieve with clumping boundary conditions. Finally, an analytical model, taken account only gradient in the quasi-static plateau stress, is developed to predict the top skin pic peak load of the graded sandwich panel.
Simulation of phase transitions and strength evolution in quartzite in shock experiments
Authors: Kovalenko Mikhail , Shalkovsky Denis , Petrovtsev Aleksandr , Pavlenko Aleksandr , Malyugina Svetlana , Yusupov Dmitriy
Published: September 2021

Quartzite is a basic rock constituent. It has a complicated phase diagram where besides a low-pressure phase (α-quartz), two high-pressure solid ones are present – coesite and stishovite. Also present are the hightemperature cristobalite and tridymite phases with very small stability regions. In shock experiments, the transition to coesite almost never realizes and the transition from α-quartz to stishovite proceeds in a strongly nonequilibrium regime characterized by metastability and a long transition time. Quartzite is polycrystalline quartz with small amounts of impurities. The paper describes experiments with samples of Pervouralsk quartzite with mass fractions of SiO2 above 96%.
Programming Strain Rate Dependency into Mechanical Metamaterials
Authors: Patil Sankalp , Ganzenmüller Georg
Published: September 2021

This work presents an approach to introduce significant strain rate sensitivity into metallic metamaterials that are manufactured via additive manufacturing, where the base material employed will typically have a weak strain rate sensitivity. Here, we employ friction between the rough surfaces as the strain-rate dependent mechanism, whose magnitude is tunable by optimizing the geometry. The design along with the preliminary simulation results of the friction unit cell is presented. This work will quantify the effects of geometrical parameters on the dissipated energy.