Steady Growth Stage Research Articles

Experimental study of type-I crack propagation in rock monitored by fiber Bragg grating

The occurrence of rock mass engineering disasters can be reduced significantly by obtaining the key information in the process of rock internal fracture accumulation and evolution through advanced monitoring means and taking certain preventive measures. Through fiber Bragg grating monitoring tests of the type-I crack propagation in rock, the spectral characteristics of the fiber Bragg grating in the process of rock failure were analyzed, the bandwidth expansion was extracted to characterize the local tensile strain during the crack propagation process, and the damage variable based on the bandwidth expansion was calculated to describe the type-I crack propagation process. The research results showed the following: (1) The fiber Bragg grating generated a non-uniform local tensile strain during type-I crack propagation. The bandwidth expansion of the wave spectrum was positively correlated with the local tensile strain. The change in the characteristics of the wave spectrum could provide the local real strain in the process of crack propagation. (2) During the steady propagation of the type-I crack, the bandwidth increased obviously, while the number of acoustic emission events was relatively small, and most of them were in the process zone. The gentle increase in the bandwidth corresponded to the unstable growth stage of the type-I crack, which could be used as a precursor of rock sample instability. During loading, the maximum tensile strain of the type-I crack was 6 %, while the maximum shear strain reached 1.8 %, primarily attributed to tensile failure. The average value of fracture toughness KIC, based on the equivalent linear elastic fracture mechanics model, was determined to be 1.21 MPa·m1/2, and the average value of fracture energy Gf was calculated as 57.7 N/m. The variation of peak reflectivity in fiber Bragg grating was associated with the closure of pre-existing defects and the propagation of microcracks in rocks, resulting in unstable shear strain at crack extension sites. (3) The damage variable D defined by the bandwidth broadening began to become concentrated and accumulated in the crack steady growth stage, and it increased slowly in the crack intensification and evolution stage. The grating was sensitive to changes when it was pasted to the surface at 90°, but it could easily fracture or become unable to capture spectral signals in time. Based on a comprehensive comparison, the monitoring effect was the best when the grating was pasted at 60° relative to the crack.

Bibliometric and visual analyses of advancements in chronic kidney disease management.

Chronic kidney disease (CKD) is characterized by high incidence, prolonged course, significant health damage, and a heavy societal burden. Understanding the history and content of CKD research is crucial to further its recognition and management, in addition to reducing its individual and societal burdens. This study aimed to assess the management history of CKD to provide a foundation for clinical medical staff to systematically understand its evolution. The Web of Science Core Collection database was screened for CKD management studies published between January 1, 1948, and December 31, 2021. From the search results, we performed statistical descriptions of the publication date, volume, and type. Using VOS-viewer 1.6.19, variables from the included articles were obtained for keyword co-occurrence clustering and sequence analyses to determine research themes, segment phases based on publication volumes over varied timeframes, assess the dynamic progression of CKD management, and anticipate future research trends. In total, 26,133 articles met the inclusion criteria. The analysis revealed 3 stages of CKD management research: the slow development stage (1948-1998), which was initiated by epidemiological studies without ideal clustering; the steady growth stage (1999-2010), which was focused on CKD complication management and quality-of-life research; and the rapid development stage (2011-2022), which was dominated by 7 major clusters, mainly regarding the treatment and management of severe conditions and management patterns. The CKD research journey is comprised of 3 stages, the contents of which form an interconnected research model. Future research should focus on the establishment of management models and the application of intelligent management tools. Furthermore, this work can serve as a reference for the further expansion of research in this field and in improving its management.

Experimental study on the deformation and failure mode of surrounding rocks of a tunnel in a jointed rock mass

The existence of jointed rock masses in tunnels is a key problem that leads to the deformation and instability of the surrounding rock. Based on the engineering background of the Qingdao Metro, a physical model and a numerical model are constructed to analyze the mechanism of deformation and instability of the surrounding rock of a jointed tunnel using model blocks that conform to the characteristics of joint distribution. The results show that during the whole test process, the cracks between the blocks in the tunnel arch are in the “development − stability − closure − penetration” state. Finally, the block falls in the left area of the tunnel, and the corresponding anchor axial force transits from the linear growth stage to the steady growth stage. After the axial force of the rock bolt suddenly decreases in the loading stage, the bolt enters the stability stage, and finally, S-shaped failure occurs when the surrounding rock is unstable. Under the action of a prestressed rock bolt, the normal stress and radial stress of the rock mass increase, and the difference between the major and minor principal stresses decreases significantly. The radial stress on the surrounding rock surface of the arch is approximately 8 % greater than that in the traditional rock bolt scheme, which improves the strength reserve of the rock mass. In the field test, the prestressed rock bolt can control the deformation of the surrounding rock in the arch within 2 ∼ 5 mm, which provides a reference for the control of the surrounding rock in jointed tunnels.

Study on the spatial and temporal evolution of industrial carbon emission efficiency and influencing factors based on improved Adaboost regression algorithm

Abstract This paper first combines the traditional Adaboost iterative algorithm and logistic regression algorithm to construct an improved Adaboost based regression algorithm. In order to solve the problem of the redundant amount or insufficient amount of output of industrial carbon emissions, the SBM model is divided into two stages, and by merging this method, the industrial carbon emission efficiency measuring model is created, While the Global Moran’s I index is used to assess the geographical impact of industrial carbon emission efficiency. Additionally, a model of the influence of emission efficiency based on the geographical effect is built through the selection of the explanatory variables of the influencing factors. According to the study, the industrial carbon emission efficiency is growing at an annual rate of 1.8% during the period of fast expansion, 0.4% in the steady growth stage, and the Z value of STI is 0.38 is significant in spatial autocorrelation.

Characteristics and development of damage in the interface of polyimide multilayer films under a repetitive-frequency-pulsed voltage

To study the initiation and development of interfacial electrical damage in multi-layer dielectrics, an aging test of 3-layer polyimide films was conducted under pulsed voltage with a repetitive frequency of 500 Hz and a maximal amplitude of 30 kV. The variation in the damage morphology with the number of applied pulses was analyzed by a statistical method. The circuit current and partial discharge at different aging stages was measured, and the Fourier transform infrared spectrum analysis results of the aged and unaged sample regions were compared. The results demonstrate that the partial discharge in the dielectric interface gap, which is unavoidable in manufacturing, is the main cause of damage. It initiates from the interface and grows into the interior of the dielectric with the application of pulses. When there are no macroscopic defects on dielectric films, damage presents a punctiform morphology. The damage process can be divided into the following three stages: surface roughening damage, steady growth stage of damage points, and pre-breakdown stage. Differing from dielectrics without macroscopic defects, dielectrics with original void defects present transverse dendritic damage channels that initiate from the edge of the defect.

Examination of the Effects of Different Frequencies on Rock Fracturing via Laboratory-Scale Variable Amplitude Fatigue Loading Experiments

In this study, the characteristics of the fracture evolution of argillaceous shale under increasing-amplitude loading were investigated. The GCTS RTR-2000 test system and in-situ acoustic emission (AE) monitoring were employed to execute the tests. The following results were observed. (1) The strength, deformation, and fatigue life increased with the frequency, and the morphology of the hysteresis curve changed regularly with time. (2) The cumulative damage of the rock at the location in which the stress amplitude suddenly increased exceeded that at the fatigue loading stage. The AE count and AE energy were affected by the loading frequency. (3) The secant modulus exhibited different values for different loading frequencies; the smaller the loading frequency, the fewer loading stages the samples experienced, and the faster the secant modulus decreased. The change in Poisson’s ratio over the entire process was composed of a steady growth stage and a rapid growth stage. (4) The rock exhibited two stages of damage evolution, with rapid damage accumulation occurring at the beginning of the loading and relatively smooth damage occurring thereafter. This study developed a cumulative fatigue damage model that can adequately fit the accumulated damage during the fracturing process. The experiments revealed that variable amplitude fatigue loading at different frequencies significantly influences the damage deterioration and the failure law of the rock. The results are expected to improve the understanding of the frequency effect on the fracture behavior and help predict the lifespan of rock structures. This is of great significance to the promotion of slope management, landslide disaster prevention, and mine reuse at the West Open-pit Mine.

Analysis of damage characteristics and energy evolution of salt rock under triaxial cyclic loading and unloading

The gas injection, water-soluble excavation, and gas recovery process in the gas storage salt cavern can be regarded as the loading and unloading process of the surrounding rock stress. By conducting triaxial loading and unloading tests on salt rock samples, several findings are presented: 1) The failure formed in the rock sample is a shear failure mode when confining pressure is below 15 MPa, and after confining pressure exceeds 15 MPa, it is bulging in the middle part of sample. The scientific strain is proved to be more suitable for describing the deformation of salt rock sample than the engineering strain. 2) During the unloading-reloading process, the produced stress difference is small at the beginning of unloading, while the rock undergoes more stress loss in the post-peak stage than that in other stages. 3) When the strain increases to reach a specific value, the dissipative energy difference increases with higher confining pressure. 4) Higher confining pressure improves the initial damage degree to the sample. But under different confining pressures, the damage variable has a similar evolution trend, which reaches a steady growth stage with the loading/unloading cycles gradually.

Fatigue performance characterization of styrene-butadiene-styrene and crumb rubber composite modified asphalt binders with high crumb rubber contents

Recycled from waste tires, crumb rubber (CR) is a common additive material using in transport infrastructures to improve the mechanical performance of asphalt mixture. The styrene-butadiene-styrene (SBS) and CR composite modification technology were employed to prepare SBS/CR composite modified asphalt (CMA) binders. To study the effect of CR contents and control modes on the fatigue performance of asphalt binders, the Dynamic Shear Rheometer (DSR) tests, including stress/strain sweep tests and controlled-stress/strain time sweep tests, were conducted to calculate the fatigue crack density as loading cycles. Based on the test data, the fatigue crack density evolution and the modified Paris’ law were used to characterize the fatigue performance of SBS/CR CMA binders. A unified fatigue parameter was proposed to evaluate the fatigue resistance and optimize the CR content of SBS/CR CMA binders under two control modes. Results demonstrated that the fatigue crack density only experienced two stages (the crack initiation stage and the steady growth stage) under the controlled-strain loading, while the asphalt binder sample shows obvious structural failure (e.g., stepping into the unsteady growth stage) under controlled-stress loading. The smaller value of the proposed index, lnA/(n+1), indicated the better capacity of fatigue crack resistance and that of a certain type of asphalt binder under two control modes were almost identical. Furthermore, the value of SBS/CR CMA binder with 40 wt% CR was −6.81 showing the best fatigue performance among these asphalt binders, and the CR contents and the values of proposed index followed a linear relationship.

Isobaric Tags for Relative and Absolute Quantitation-Based Proteomics Analysis Provides a New Perspective Into Unsynchronized Growth in Kuruma Shrimp (Marsupenaeus japonicus)

Unsynchronized growth is a common phenomenon in farmed crustaceans. The underlying molecular mechanism of unsynchronized growth of crustaceans is unclear. In this study, a comparative proteomic analysis focusing on growth differences was performed using kuruma shrimp Marsupenaeus japonicus, an economic crustacean species, as the model. The study analyzed kuruma shrimp at fast growth stage and steady growth stage from both fast growth group and slow growth group by an Isobaric tags for relative and absolute quantitation (iTRAQ)-based quantitative proteomic analysis method. A total of 1,720 proteins, including 12,291 peptides, were identified. Fifty-two and 70 differentially expressed proteins (DEPs) were identified in the fast growth stage and steady growth stage, respectively. Interestingly, 10 DEPs, including 14-3-3-epsilon-like, GPI, GPD1, MHC-1a, and MHC-1b, were presented in both growth stages. In addition, all these 10 DEPs shared the same expression tendency at these two growth stages. The results indicated that these 10 DEPs are potential growth biomarkers of M. japonicus. Proteins associated with faster growth of M. japonicus may promote cell growth and inhibit cell apoptosis through the Hippo signaling pathway. The fast growth group of M. japonicus may also achieve growth superiority by activating multiple related metabolic pathways, including glycolysis, glycerophospholipid metabolism and Citrate cycle. The present study provides a new perspective to explore the molecular mechanism of unsynchronized growth in crustacean species.

Study Progress of Important Agricultural Heritage Systems (IAHS): A Literature Analysis

Important Agricultural Heritage Systems (IAHS), as a new type of heritage, has received extensive attention from the international scientific communities. With the increase of IAHS research, reviews on it have been conducted by many scholars. However, visualized research to show future research trends of IAHS are lacking. Therefore, using metrology analysis methods, this study aims at presenting the progress of research and the general development trends of Globally Important Agricultural Heritage Systems (GIAHS) in the world from 2006 to 2020 to provide ideas for the development of countries or regions in the future. This study mapped 292 literatures from Web of Science core collections from 2006 to 2020 by CiteSpace software. The results show that research on IAHS from 2006 to 2020 experienced two stages: the fluctuating increase stage, and the steady growth stage. Author groups from China, Italy, the USA, Japan, etc., contributed many papers on IAHS. Institutions including the Chinese Academy of Sciences, the University of Florence and the University of Padua in Italy, etc., have a relatively high influence on international IAHS research. Agriculture Ecosystems & Environment is the most cited journal. Agricultural Heritage Systems, regeneration, agriculture, agroforestry, dry-stone wall, social capital, instability, and agricultural biodiversity have been hotspots in the past 15 years. The research themes mainly focus on GIAHS, tourism, livelihood assets, and direct georeferencing. Authors in different regions concern different research themes. In the future, the fields of applications and microscopic views, social sciences, applications of standardized quantitative research methods, and broadened international cooperation should be paid more attention.

Behavioral strategy: mapping the trends, sources and intellectual evolution

PurposeThis paper presents a comprehensive review of academic research dedicated to the field of Behavioral Strategy. Based on a series of Bibliometric and network analyses, the paper identifies the prominent trend and growth patterns pertaining to the evolution of this important strategic management subfield; it documents which particular journals, articles and authors have most influenced its development, and it maps the intellectual structure and network of authors, publications and countries. Finally, the paper considers the substantive research themes emerging from the analyses reported, in terms of their implications for future work.Design/methodology/approachThe authors undertook a series of Bibliometric and network analyses of 217 relevant articles, published between 1975 and 2020, in journals listed in the Scopus database, using R-studio and VOSviewer. Articles incorporated in the study were selected based on relevant key terms searched from the title, abstract and list of keywords associated with each publication.FindingsThe results demonstrate that behavioral strategy has enjoyed robust and sustained growth, with widespread impact across many areas of the heterogeneous business and management field as a whole. Three distinct periods are identified: an infancy stage (prior to 1999); a steady growth stage (1999–2010); and a take-off stage (2011 onwards). The top three journals in terms of content coverage, based on the number of relevant articles published in relation to behavioral strategy, are Strategic Management Journal, Advances in Strategic Management (AiSM) and the Journal of Management, while the top three most influential journals, in terms of citations pertaining to Behavioral Strategy, based on an analysis of citations in the Scopus database, are Strategic Management Journal, Academy of Management Perspectives and Journal of Management Studies. Gerard P. Hodgkinson and Thomas C. Powell are the most prolific authors. The emerging themes based on intellectual structures have been identified as Behavioral Strategy, Behavioral Theory of Firm; Strategic Leadership and Dynamic Capabilities; and Strategic Cognition and Decision Making.Practical implicationsThe study contributes to knowledge advancement concerning Behavioral Strategy by opening new possibilities to discover important research areas.Originality/valueThe study is the first of its kind on Behavioral Strategy providing a comprehensive systematic literature review.

Energy-based characterization of the fatigue crack density evolution of asphalt binders through controlled-stress fatigue testing

Fatigue crack behavior of asphalt binder plays an important influence on the fatigue performance of asphalt pavements. To evaluate the fatigue crack density evolution within the steady growth stage of #70 unmodified asphalt binder and SBS modified asphalt binder, the crack initiation and propagation were characterized based on Griffith theory and modified Paris’ law, respectively. Aiming to calculate the horizontal length of crack initiation (a), the surface free energy of those two asphalt binders were calculated by contact angle measured with Wilhelmy plate test. Also, the stress sweep tests and time sweep tests were performed using Dynamic Shear Rheometer (DSR) to obtain the mechanical parameters of asphalt binders for calculation of fatigue crack density (ϕ) and dissipated pseudo strain energy (DPSE). They were fitted by modified Paris’ law, and coefficients n and A were determined. Results show that a for two asphalt binders increase with the increasing stress level and SBS modified asphalt binder shows a larger crack size in crack initiation, which means that SBS modified asphalt binder shows a better crack initiation resistance compared with unmodified asphalt binder. The ϕ and DPSE within the steady growth stage follow the linear relationship, indicating that the unit DPSE causes the equal amount of increase in ϕ. In addition, the A and n are independent on the stress levels. They are fundamental material properties and there is a linear relationship between the log(A) and n. SBS modified asphalt binder processes the better fatigue crack resistance because of the smaller value of n.

Development Trend and Segmentation of the US Green Building Market: Corporate Perspective on Green Contractors and Design Firms

In the past decade, the architecture, engineering, and construction industry has witnessed increasing growth in the green building market and continues to expect a promising future. Although companies in the industry have played a significant role in developing the green building market, scarce studies have analyzed changes in the market from the perspectives of these corporations. Also, few studies classify green building companies by characteristics. To fill these gaps of knowledge, we explored the characteristics of the US green building market from a corporate perspective, specifically investigating green contractors and design firms. We first collected data of 464 top US green building companies identified by the Engineering News-Record over the past decade and explored the development trend of the green building market, based on the green revenue generated by these companies. We found that the general growth trend in the US green building market in the past decade could be divided into three stages: a rapid-growth stage (2000–2008), a steady-growth stage (2009–2013), and a maturity and transformation stage (2014–2016). We then categorized the 464 organizations into three groups with distinct characteristics by k-means cluster analysis techniques, including mature green building companies, sector-oriented green building companies, and primary-stage green building companies. This study provides the academic and practitioner communities with a holistic understanding of the development of the US green building market from the view of burgeoning companies. Corporate-level management systems and sustainable practices of the three clusters of green building companies also provide guidance for construction companies in the various stages of transformation towards sustainability to adopt different strategies.

Analysis of Cracking Development and Mechanical Characteristics of High-Filled Cut-and-Cover Tunnel

The cut-and-cover tunnel (CCT) construction scheme has led to the popularity of high-filled cut-and-cover tunnel (HFCCT). HFCCT possesses a backfilling height of 30–50 m. However, such a high soil column produces a large force on the structure and the structure is prone to crack, causing structural damage and difficulty in normal use. In order to provide a reference for the structural safety assessment of HFCCT, we conducted a similarity model test to study the variation law of the development of crack, displacement, and internal force of HFCCT with a coefficient of λ (the ratio of the backfilling height to the height of the cut-and-cover tunnel). In the test, a 1:20 similar scale CCT model with slope angle 70° and groove width ratio 1 was built using data from the HFCCT on the Lanyu Line. The backfilling process on site was simulated in a simulation box (360 cm long, 120 cm wide and 209 cm high). A numerical model was also built using PFC2D to verify the accuracy of the model test and further explain the crack formation mechanism of the HFCCT from a microscopic perspective. The results show that with the increase of the coefficient of λ, the bearing stage of the CCT can be roughly divided into three stages: steady growth stage, rapid growth stage, and accelerated growth stage. Furthermore, the development of cracks is closely related to the displacement and internal force of the CCT. The larger the displacement of the CCT, the greater the instability of the structure and the larger the ratio of the bending moment to the internal force, which causes the crack to develop faster.

Dynamic Analysis of the Coupling Coordination Relationship between Urbanization and Water Resource Security and Its Obstacle Factor.

Water resource security is an important condition for socio-economic development. Recently, the process of urbanization brings increasing pressures on water resources. Thus, a good understanding of harmonious development of urbanization and water resource security (WRS) systems is necessary. This paper examined the coordination state between urbanization and WRS and its obstacle factors in Beijing city, utilizing the improved coupling coordination degree (ICCD) model, obstacle degree model, and indicator data from 2008 to 2017. Results indicated that: (1) The coupling coordination degree between WRS and urbanization displayed an overall upward tendency during the 2008–2017 period; the coupling coordination state has changed from an imbalanced state into a good coordination state, experiencing from a high-speed development stage (2008–2010), through a steady growth stage (2010–2014), towards a low-speed growth (2014–2017). (2) In urbanization system, both the social and spatial urbanizations have the greatest obstruction to the development of urbanization-WRS system. The subsystems of pressure and state are the domain obstacle subsystems in WRS system. These results can provide important support for urban planning and water resource protection in the future, and hold great significance for urban sustainable development.

Two-dimensional phase-field simulations of competitive dendritic growth during laser welding

A phase-field model is applied to study competitive dendritic growth between different grains with different crystalline orientations during laser welding of Al-Cu alloy. An unfavorable oriented (UO) grain is set to locate between two favorable oriented (FO) grains to study the dendritic growth behaviors at not only converging grain boundary (GB) but also diverging GB. It is found that the cellular dendrites appear firstly nearby the GBs at initial instability stage. At early competitive growth stage, the UO misalignment angle influences the competitive dendritic growth at both GBs. After completely entering competitive growth stage, the leading dendrites that are much faster than other dendrites at GBs firstly grow in lateral direction. The side branches growing from leading dendrites block growth path of nearby dendrites and change the UO/FO grain widths. The converging GB deflection angle and the side branch development at diverging GB as characteristic competitive dendritic growth behavior at relatively steady growth stage also significantly affect UO and FO grain widths. The numerical results are basically consistent with microstructure obtained by experiment.

Energy Dissipation and Storage in Underground Mining Operations

In this paper, we focus on the energy alteration during longwall mining in an attempt to mimic the conditions of a coal mine in Western Turkey. We verify the proposed model using existing analytical and numerical solutions in terms of stress components. Based on the verified numerical model, the energy balance during longwall retreat is studied rigorously. It is found that excavation-induced increment of external work increases linearly with time, while the stored strain energy increment is quadratic. Meanwhile, the strain energy increment rate gradually decreases with longwall progress because of excavation-induced higher stored energy within the adjacent coal block. The energy dissipation process during lonwall mining, corresponding to crack propagation, is divided into four stages, namely initiation stage, steady growth stage, sharp increment stage, and stabilisation stage. Our results provide new insights into energy evolution during longwall mining both from the reversible and irreversible points of view. The current paper shows, for the first time, that the extended finite element method is suitable to describe the crack propagation during longwall mining. The excavation induced crack propagation in the roof strata predicted by the model is in agreement with the “arch-shaped” patterns obtained using laboratory tests and Discrete Element numerical simulations.

Cellular automaton modeling for dendritic growth during laser beam welding solidification process

A modified non-equilibrium cellular automaton (CA) model is proposed to simulate the dendrite growth along the fusion boundary under transient conditions during the solidification process of laser beam welding (LBW) pool. The main non-equilibrium solidification effects, including solute trapping, deviation of the liquidus line slope, and kinetic undercooling, are taken into consideration in this modified CA model. The evolution of dendrite morphology, concentration field, and velocity field was investigated. Four growth periods, i.e., the initial stable period, the instability period, the competitive growth period, and the short-term stable period, were observed during the solidification process of LBW pool. The dendrite growth patterns were different in these periods due to the transient solidification conditions. The solute distribution predicted by this modified CA model showed similar trends to that predicted by the previous phase field model. The dendrite tip velocity was significantly influenced by the thermal undercooling and constitutional undercooling in the LBW pool, and the tip velocity field can be divided into three stages, i.e., the planar growth stage, competitive stage, and short-term steady growth stage. In addition, further comparison between the simulated dendrite morphology and experimental dendrite morphology was performed. Results showed that the simulated morphology of dendrites agreed well with the experimental results. In particular, the primary dendrite arm spacing predicted by this model was in good agreement with that obtained from experiments.

Dynamic modeling of bubble growth in vapor-liquid phase change covering a wide range of superheats and pressures

Bubble growth in superheated liquid is a fundamental process in vapor-liquid phase change which occurs widely in thermal and chemical engineering. The strong coupling of heat, mass and momentum transfer at the interface brings difficulties to accurately predict the dynamics of bubble growth. At present, bubble growth under three extreme conditions, i.e. the very early growth stage, low superheats and low pressures, cannot be well described by traditional asymptotic solutions. In this work, a mathematical model was presented for better prediction of bubble growth in a superheated liquid. The model was derived from the equations of motion for a bubble and took account of the heat and mass balances at the interface. The model was validated with a series of experiments from the literature, covering a wide range of operating conditions. The newly proposed model can well predict the features of bubble growth at the very early stage (less than 10−6s), for superheats varying from 0.8K to 36K and for system pressures reduced from 1.0atm to 0.0124atm. Analyses on the thermodynamics and hydrodynamics manifested that the bubble growth was characterized by three typical stages, i.e. a thermal delay stage, a fast expansion stage and a steady growth stage. The time lengths of these stages were related to the levels of superheat or system pressure. Characteristics of these stages were further discussed and the roles of interfacial forces under the different operating conditions were demonstrated.

Evaluation on Tensile and Fatigue Crack Growth Performances of Ti6Al4V Alloy Produced by Selective Laser Melting

Additive manufacturing (AM) technologies are increasing in importance for aerospace application, where the demand for a fundamental understanding and predictability of static and dynamic material properties are high. As the most widely used and studied alloy for this technology, Selective laser melting (SLM) produced Ti6Al4V alloy is evaluated on tensile and fatigue crack growth (FCG) performances at RT and 400℃. Conventionally manufactured Ti6Al4V alloys are concerned for comparison. Different orientations are considered to investigate the anisotropy of tensile and FCG behavior. The results show that, the tensile properties at RT and 400℃ are highly dependent on the specimen orientation relative to build direction. The FCG resistance is related to specimen orientation in the near threshold region but no relationship with specimen orientation in the steady growth stage at RT. The FCG resistance is much less influenced by specimen orientation at 400℃. The tensile strength at RT and 400℃ of SLM alloy reaches even exceeds the strength level of conventionally manufactured alloys such as forging, bar and casting. The steady stage FCG resistance under stress ratio of 0.1 of SLM alloy is also comparable to conventionally manufactured alloys. The SLM alloy shows higher FCG resistance under stress ratio of 0.1 than 0.5, but the da/dN-△K curves of the two stress ratios are very close to each other. The steady stage FCG rate at RT is slower than 400℃ in the lower △K region and faster in the higher △K region.