Friction Sensitivity of Nitramines. Part Ⅰ:Comparison with Impact Sensitivity and Heat of Fusion

Fractions of β-HMX(β-1,3,5,7-tetranitro-1,3,5,7-tetrazocane) have been used to demonstrate the mutual relationship between friction and impact sensitivities.Inclusion of an additional twelve nitramines into this scenario resulted in a series of partial relationships,which were determined from the molecular structure of these substances.It was also found that there is a relation between increasing heats of fusion of the nitramines studied and their decreasing friction sensitivities.Comparison of friction sensitivity with heats of fusion,ΔHm,tr of the studied nitramines shows that the increase in ΔHm,tr values is more or less connected with a decrease in friction sensitivity.

Effect of Heat Treatment on Hardness and Impact Toughness of CuCr Containing RE Alloy

The effect of heat treatment on hardness and impact toughness of CuCr containing rare earth alloy was studied by means of metallographic, XRD, SEM/EDX, TEM and mechanical property test. The results show that the heat treatment can change the hardness of CuCr alloy, and has smaller influence to its impact toughness. The optimum properties of CuCr containing RE alloy could be obtained by aging treatment at 500 ℃ for 2 h. And the causes of the above changes and the function of RE were analyzed.

Physical, Psychological, and Social Health Impact of Temperature Rise Due to Urban Heat Island Phenomenon and Its Associated Factors

The Urban Heat Island Effect（UHI）has now become a commonly observed phenomenon worldwide.Indeed,it has become a significant environmental effect of urbanisation.In Malaysia,research results showed that UHI effects are very evident in several cities such as Kuala Lumpur and Putrajaya.UHI effect has long been observed to cause temperature of cities.

Impact of Vibration Models on Heat Capacities of HF Molecular System

Based on the analysis of completeness and finiteness of HF molecular vibrational levels, HF systemic vibrational heat capacity is studied with quantum statistical and full set of vibrational energy level determined AM (algebraic method). The results show that correct vibrational description and vibrational energy level set of HF system are key factors in calculating heat capacity, HF heat capacity data determined by AM energy spectra {Eυ} are much superior to the ones of harmonic oscillator model, AM results are agreement with experiment data.

Environmental Impact Assessment for an Absorption Heat Transformer

This study presents the environmental impact assessment of an absorption heat transformer designed to recover 1 kW of thermal energy from each 2 kW of waste heat supplies. The net contribution of the heat transformer is a load avoided of 0.665 kg CO2 equivalents;the recovery process avoids 0.729 kg CO2 equivalents and the major contribution to the environment impacts is the pumping process with 0.0437 kg CO2 equivalents for each 1 kWh recovered. The study results show that absorption heat transformer is a good environmental option because it produces useful energy from waste heat and the final result is an environmental impact diminution.

Effect of Heat Input on the Microstructure and Mechanical Properties of 07MnCrMoVR Weld Joints

As a new type of low cracking suscepbility high strength steel,07MnCrMoVR steel has excellent weldability,with low carbon equivalent and cold cracking susceptibility coefficient.However,there are still some problems when this steel is on the outdoor actual welding condition,such as having some extend cold cracking suscepbility and embrittlement of heat affected zone.Currently, researching works for the welding of this steel mostly focus on the evaluation the weldability of it,only few works are concentrated in how the heat input affecting the embrittlement of HAZ.The goal of this research is to study the effect of heat input on the embrittlement of the heat affected zone so as to get the optimal welding heat input range for it.In this paper,38 mm 07MnCrMoVR steel made by Shougang is welded by manual arc welding technology,and the effect of heat input on the microstructure and mechanical properties of weld joints is also investigated by use of optical microscope（OM）,scanning electron microscope（SEM）,mechanical properties testing machines and Viker hardness tester.The microstructure and fractography observation results and the mechanical properties testing results indicate that the 07MnCrMoVR steel made by Shougang has a wide adaptable range for heat input,and when the heat input is in the range of 15-42 kJ/cm,the toughness of the weld joints is well.With the increase of heat input,the impact toughness of weld zone and heat affected zone decrease,whereas the tensile strength of the weld joints does not change at all.The microstructure of the weld is acicular ferrite with small amount of proeutectoid ferrite,and with the increase of heat input,the ratio of proeutectoid ferrite and the amount of M-A constituent increase,as well as the grain size and the width of the bainite lath in coarsened grain heat affected zone. Fractography results show that with the increase of heat input,the number of dimples in impact fracture specimens decreases,and the cleavage patterns increase,inducing the fracture from ductility to embrittlement.This research provides a theory support for guiding the penstock constructor how to use 07MnCrMoVR steel in actual welding.

Effect of Heat Input and M-A Constituent on Microstructure Evolution and Mechanical Properties of Heat Affected Zone in Low Carbon Steel

Microstructure evolution and impact toughness of simulated heat affected zone（HAZ） in low carbon steel have been investigated in this study. Thermal simulator was used to simulate microstructure evolution in HAZ with heat input of 10-100 kJ/cm welding thermal cycle. Results indicated that microstructure of HAZ mainly consisted of acicular ferrite（AF） inside grain and high volume fraction of grain boundaries ferrite（GBF） at prior austenite boundaries; the size of GBF and effective grain size increased with increasing heat input. Excellent impact toughness（more than 150 J at-40 ℃） was obtained in HAZ with heat input less than 50 k J/cm. When heat input was 100 kJ/cm, the impact toughness of HAZ decreased to 18 J because of the presence of large M-A constituent with lath-form in HAZ, assisting the micro-crack initiation and decreasing the crack initiation energy seriously. Effect of inclusions on acicular ferrite transformation in HAZ was also discussed.

Occupational Heat Stress in the Floriculture Industry of Ethiopia: Health Risks and Productivity Losses

Background: The Ethiopian flower industry is growing fast with successful diversification of export products under greenhouse structures. Higher temperatures in the greenhouses pose a serious threat to the health of workers and add to the risk of occupational heat stress. Excessive heat in workplace settings also reduces work capacity and labour productivity. This study aims to investigate the level of heat exposure, and workers’ and managers’ perceptions and behavioural responses towards extreme heat exposure in a warming climate. Methods: We used the Wet Bulb Globe Temperature (WBGT) measured in representative greenhouses to capture the heat exposure during hotter and cooler seasons following ISO 7243 (generally risk of heat stress occurs when WBGT exceeds 26°C). A comparative cross-sectional study design with a stratified sampling method was used to assess occupational heat stress and workers’ perceptions of the impact of heat on their health and productivity in six different floriculture greenhouses in Ethiopia representing three different agro-ecologies and products. A questionnaire survey was conducted (30 managers/supervisors and 305 workers;76.1% female) to capture perceptions on heat exposures, symptoms of potential health impacts, productivity losses and coping mechanisms. Results: Heat exposure varied across different agroecologies, product types and greenhouse materials with a median WBGT Index of 25.5°C and a range from 18.1°C to 31.5°C. The impact of heat stress also varied across different employment sectors and geographical regions. Overall, workers in cut-flower greenhouses are exposed to higher than recommended WBGT Index (26°C) for 3 - 6 working hours daily. 65% of the managers reported that heat stress has a significant impact on the workers’ labour productivity, but do not have guidance about working in hot conditions. Workers reported more heat-related health issues and reduced productivity, especially in the mid-altitude greenhouses. About 50% of the workers reported that heat exposure decreased work productivity during hot hours. Sweating, exhaustion, heat-rashes, dehydration, crumps, nausea and headache were self-reported health issues. Labour productivity losses ranged from no loss to 19.5% in the mid- and low-altitudes. Conclusions and Recommendations: Excessive workplace heat in the greenhouses is both an occupational health hazard and detrimental to productivity in the floriculture industry. However, the level of understanding and actions on the ground regarding occupational heat stress are low. The code of conduct in place now does not consider the occupational heat stress issues. Multiple actions (engineering, management, training and policy-related recommendations) have to be implemented by Ethiopian Horticultural Producers and Exporters Association (EHPEA) and farm owners to mitigate heat stress and loss of productivity. Designing and implementing these heat prevention strategies and incorporating them into the code of conduct is in the interests of both employers and employees.

Effect of Heat Treatment on Microstructure and Mechanical Properties of NF6357A Cast Alloy for Wear Resistance Application

The solidification structure of the as-cast consists of the matrix structure that is predominantly austenite and precipitated chromium carbide along the grain boundary. Under these circumstances and where the level of impact is relatively modest, such alloys in as-cast condition will perform. However, at higher levels of impact energy, a point is reached where excessive stress are built up within the component and eventually the materials strength is exceeded and the outcome is complete failure in a characteristic stress fracture mode. If this is to be prevented, it is therefore imperative that the casting be subjected to appropriate heat treatment, to obtain a structure which consist of Cr7C3 carbide and martensite at a hardness range of 650-750HB. The microstructure of NF6357A cast chromium steel containing 2.59% C- 0.7%Si-0.91%Mn-18.54%Cr-0.019%P-0.01%S- balance–Fe after appropriate heat treatment such as quenching and tempering process have been characterised by means of optical microscope, micro hardness tester, optical emission spectrometer and charpy testing machine. The results show that oil quenched samples were found to retained microstructural consistency for casting thicker than 120mm section. For economic argument, air quenched castings of less than 120mm thickness is not only cheaper alternative, but it is also environment friendly. The fracture toughness was found to be fairly consistent between 2.4-2.6%C range. However, at higher carbon level, the fracture process is dominated by the presence of segregated carbide network which act as a weak link in the microstructure. This weak link encourages dislocation pile-up and impaired material toughness.

Effective Microstructure Unit in Control of Impact Toughness in CGHAZ for High Strength Bridge Steel

The high strength bridge steel was processed with the simulated coarse grain heat affected zone（CGHAZ） thermal cycle with heat input varying from 30 to 60 kJ/cm, the microstructures were investigated by means of optical microscope（OM）, scanning electron microscope（SEM）, electron backscattering diffraction（EBSD） and transmission electron microscope（TEM）, and the impact properties were evaluated from the welding thermal cycle treated samples. The results indicate that the microstructure is primarily composed of lath bainite. With decreasing heat input, both bainite packet and block are significantly refined, and the toughness has an increasing tendency due to the grain refinement. The fracture surfaces all present cleavage or fracture for the samples with different heat inputs. Moreover, the average cleavage facet size for the CGHAZ is nearly equal to the average bainite packet size and the bainitic packet boundary can strongly impede the crack propagation, indicating that the bainitic packet is the most effective unit in control of impact toughness in the simulated CGHAZ of high strength bridge steel.

Effects of Zr on acicular ferrite formation in HAZ of Ti-bearing low carbon steels with high heat input of weld thermal simulations

To research the effect of Zr addition on inhibiting austenite grain growth of Ti-bearing low carbon steels, two steels with different Zr contents were prepared using a laboratory vacuum induction furnace. The performance of HAZ under weld thermal simulations was investigated. The impact toughness, microstmcture and the second-phase particle performance of HAZ under weld thermal simulations were investigated. The HAZ toughness was improved from 13 J to 87 J by addition of 0.010 % Zr into the steel, with the fracture mechanism changing from cleavage fracture to toughness fracture, which was mainly attributed to the second-phase particles that were potent to nucleate acicular ferrite in HAZ during welding. It was concluded that the second-phase particles TiOx ＋ MnS, ZrO2 ＋ MIlS or TiO/＋ ZrO2 ＋ MnS were nucleated on ZrO2 or TiOx （x = 1.5,2）. This method can be applied to grain refinement by promoting the acicular ferrite formation and growth during large-scale welding, as in the cases of thick steel plates requiring higher heat inputs during welding.

Effect of heat input and postweld heat treatment on microstructure and toughness of heat-resistant steel E911 deposited metal

The microstructure of E911 deposited metal was observed and the effect of heat input and postweld heat treatment on microstructure and impact toughness was investigated. The microstructure consists of tempered martensite and residual δ- ferrite. The morphology of tempered martensite is columnar and the residual δ-ferrite is polygonal. With the increase in heat input, the width of columnar martensite grain and the size of residual δ-ferrite increased, whereas the volume fraction of residual δ-ferrite varied slightly. The impact toughness decreased as heat input increased. The result reveals that coarsening columnar martensite grain and δ-ferrite have greater effect on impact toughness than volume fraction of residual δ-ferrite. As the time of postweld heat treatment is exceeded 8h, aggregation of M23 C6occurs in some grain boundaries or lath interfaces. The partial aggregation of M23 C6 results in the decrease in impact toughness.

Influence of post-weld heat treatment on microstructure and properties in heat-affected zone of KMN steel joint

The influence of temperature during post-weld heat treatment on the microstructure and properties of KMN steel joints was investigated. The results reveal that after heat treatment, the martensite transformed to tempered sorbite, causing the softening of the resultant joints. XRD test shows that the residual austenite content decreased obviously when the joint was heattreated at 550 ℃ and 580 ℃, which degraded the impact toughness of heat-affected zone （ HAZ）. When the heat treatment temperature increased further, the dispersion strengthening from the precipitation of alloying elements improved the impact toughness of HAZ. The aggregation and coarsening of carbide also contributed to the improvement of impact toughness of HAZ.

Analysis and calculating for preheat temperature and average convection heat change coefficient in the continue annealing furnace

The aim of the thesis is to utilize essential theory of heat transfer,to use correlative expressions to calculate average convection heat change coefficient and heating temperature of strip in Jet Preheat Furnace (JPF),make the calculating results accordant with production data,and make the calculation to be used the process of production.The method is to collect:entry temperature and speed of strip,temperature and speed of N_2 - H_2,to analyse heat transfer according to length and thickness of strip,jet hole and mutual position of jet piping in JPF,to analyse heat transfer and built the physical model.In mathematic model, Martin correlative expressions are tried to calculate using the data from production,and are modified in part properly.At the same time,heat boundary condition is analysed with theory of impact jet and production data.The conclusion is obtained that boundary condition is rarely average numerical value of temperature of strip and N_2 - H_2 with impact jet condition,instead of a relation of function of temperature of strip, temperature and speed of N_2- H_2,array of jet holes,diameter of hole,distance between hole and strip,and acquired a calculating expression.In calculation of examples,the thesis collected and calculated 15 kinds of strips.The thickness of strips are 2=0.51~1.41 mm,material DQ - IF、DDQ,EDDQ,SEDDQ and 340DDQ.Main assess numerical value is temperature value after strip is heated with certain speed and within section of time.Maximum error in 9 groups of numerical value in the thesis is 3.36%comparing with production data.The correlative expressions can be used in production to adjust temperature of strip through changing speed and temperature of N_2 - H_2 and speed of strip.The correlative expressions are compiled computer process.The process can be applied in on line control of production by rapid calculating speed.

A Possible Mechanism of the Impact of Atmosphere-Ocean Interaction on the Activity of Tropical Cyclones Affecting China

In this study, tropical cyclone data from China Meteorological Administration （CMA） and the ECMWF reanalysis data for the period 1958-2001 was used to propose a possible mechanism for the impacts of air- sea interaction on the activity of tropical cyclones （TCs） affecting China. The frequency of TCs affecting China over past 40 years has trended downward, while during the same period, the air sea interaction in the two key areas of the Pacific region has significantly weakened. Our diagnoses and simulations suggest that air sea interactions in the central North Pacific tropics and subtropics （Area 1） have an important role in adjusting typhoon activities in the Northwest Pacific in general, and especially in TC activity affecting China. On the contrary, impacts of the air-sea interaction in the eastern part of the South Pacific tropics （Area 2） were found to be rather limited. As both observational analysis and modeling studies show that, in the past four decades and beyond, the weakening trend of the latent heat released from Area 1 matched well with the decreasing Northwest Pacific TC frequency derived from CMA datasets. Results also showed that the weakening trend of latent heat flux in the area was most likely due to the decreasing TC frequency over the Northwest Pacific, including those affecting China. Although our preliminary analysis revealed a possible mechanism through which the air sea interaction may adjust the genesis conditions for TCs, which eventually affect China, other relevant questions, such as how TC tracks and impacts are affected by these trends, remain unanswered. Further in-depth investigations are required.

Numerical Study by Imposing the Finite Difference Method for Unsteady Casson Fluid Flow with Heat Flux

This article presents an investigation into the flow and heat transfer characteristics of an impermeable stretching sheet subjected to Magnetohydrodynamic Casson fluid. The study considers the influence of slip velocity, thermal radiation conditions, and heat flux. The investigation is conducted employing a robust numerical method that accounts for the impact of thermal radiation. This category of fluid is apt for characterizing the movement of blood within an industrial artery, where the flow can be regulated by a material designed to manage it. The resolution of the ensuing system of ordinary differential equations (ODEs), representing the described problem, is accomplished through the application of the finite difference method. The examination of flow and heat transfer characteristics, including aspects such as unsteadiness, radiation parameter, slip velocity, Casson parameter, and Prandtl number, is explored and visually presented through tables and graphs to illustrate their impact. On the stretching sheet, calculations, and descriptions of the local skin-friction coefficient and the local Nusselt number are conducted. In conclusion, the findings indicate that the proposed method serves as a straightforward and efficient tool for exploring the solutions of fluid models of this kind.

光热性能目标下夏热冬冷地区中小学典型教室空间形态优化设计研究

随着全球能源短缺和气候变化问题的凸显,教育建筑作为社会文明进步与现代化创新的重要载体,其低碳、节能与健康的环境质量提升尤为重要。选取夏热冬冷地区中小学典型教室空间单元,以能耗、光舒适、热舒适为性能目标,基于参数化平台优化光热目标下典型教室空间的最优空间形态,分析不同类型下典型教室空间形态对光热环境的影响机理。提出了一种基于建筑多种性能目标下的多目标优化及参数分析方法框架,通过多目标优化得出建筑能耗、室内光热舒适性能的最大优化率及综合性优化方案,其中最大能耗优化率可达28.01%,最大热舒适优化率可达5.54%,最大光舒适优化率可达44.62%,并通过统计学分析得出教室空间形态参数对建筑光热能耗性能的影响特征及影响程度,为设计师提供方案参考及特征参数优化思路。

基于赫兹接触模型的发动机封严涂层碰磨力计算与优化

目的提高航空发动机的推进效率,在压气机机匣上喷涂可以减少叶尖径向间隙的封严涂层。叶尖与涂层之间的碰磨力会导致涂层脱落,且会击伤叶片,需要对碰磨力进行分析。方法采用大气等离子喷涂技术制备4种不同硬度的AlSi-PHB(聚苯酯)封严涂层,通过表面硬度测试、弹性模量测试和高速碰磨试验,分别评价封严涂层的硬度、弹性模量,以及在高速碰磨过程中不同工况下涂层受到的碰磨力;基于赫兹接触模型对叶尖与涂层之间的碰磨力进行计算,通过激光共聚焦显微镜和扫描电子显微镜对碰磨后的涂层和叶尖进行分析,同时根据接触面形态特征和温度特征对赫兹模型进行优化。结果碰磨力与涂层的硬度、叶尖转速、叶尖切入速率有关,复杂的接触表面形貌和摩擦升温会导致理论计算值与实验值之间出现偏差。结论通过优化叶尖和涂层的接触系数,同时考虑摩擦升温对涂层弹性模量的影响,可将不同工况下碰磨力计算值与测量值之间的偏差控制在1%~11%,这项研究对于指导航空发动机封严涂层的设计具有重要意义。

新型冷作模具钢9Cr5Mo2V不同热处理下的性能研究

以新型冷作模具钢9Cr5Mo2V为研究对象,通过淬回火温度对硬度的影响规律,选出5种不同的热处理工艺,对比不同工艺下模具钢的横、纵向冲击韧性、抗弯强度和耐磨性能,并与7Cr5Mo2V钢进行对照。结果表明,9Cr5Mo2V钢在1030℃淬火、520℃回火热处理下具有极佳的硬度(63.6 HRC)和耐磨性能(260.16 min/mm3);970℃淬火、520℃回火热处理后,其纵向平均冲击功最高,达62.83 J;经970℃淬火、210℃回火热处理后,9Cr5Mo2V钢具有优良的抗弯性能,纵向抗弯强度为3621.9 MPa。9Cr5Mo2V钢的纵向冲击功和抗弯强度均高于横向的纵向冲击功和抗弯强度。