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1.
Copper is among the most frequently found metallic residues in fire scene environment. Investigations on the thermal patterns produced on copper after fire scene exposure can provide important physical evidence for fire cause/origin determination. In this paper, the high temperature oxidation behaviors and the accompanying micro‐structural changes of pure copper have been studied in air and laboratory simulated kerosene‐combustion atmospheres at 600–800 °C. The oxidation kinetics, morphologies and microstructures of the oxide scales‐substrate were characterized by thermogravimetric analysis, scanning electron microscopy, energy‐dispersive spectroscopy and X‐ray diffractions. The results reveal that the increasing temperature can significantly affect the oxide properties and modify the substrate metallurgical microstructure. Especially, the presence of kerosene in the environmental atmosphere has caused accelerated oxidation and produced oxide scales different from those formed in air alone. These feature evolutions in surface oxides and substrate are expected to offer complementary insight on determining the fire characteristics, such as the exposure temperature, time period and whether liquid accelerant is involved. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
2.
编织结构复合材料力学性能的测试与分析 总被引：5，自引：1，他引：5
杨朝坤 《玻璃钢/复合材料》2002,(3):11-14
对四步法三维编织复合材料的拉伸、压缩和弯曲等性能进行了实验研究,得到了该材料的主要力学性能参数及破坏规律.实验结果表明:三维编织复合材料具有良好的力学性能,而编织工艺和编织结构对复合材料的性能有较大的影响.这些结果为进一步研究复合材料的强度失效问题奠定了实验基础. 相似文献
3.
Among the common materials, metals can be hardly destroyed by flame or the heat emanating from a normal fire. Consequently, investigation on the thermal patterns produced on metallic objects after fire exposure can provide important physical evidence for fire cause/origin determination. Aluminum alloy is widely used in our daily life and the industry; hence, it can be easily found on a domestic or industrial fire scene. In this paper, the aluminum alloy 5052 was exposed in the simulated combustion gases with and without kerosene in the range of 300 to 500°C. Mass change, morphologies, and microstructures of each sample were carefully characterized by thermogravimetric analysis, morphologic observation, and electron microscopy observation with energy‐dispersive spectroscopy analysis after exposure. As expected, the microstructure of alloy changed during high temperature exposure. At the same time, an oxide scale formed and was thickened on the surface of alloy. The results reveal that the temperature can significantly affect the growth of oxide scale and the metallurgical microstructure of alloy. It is noteworthy that the presence of kerosene in the combustion gas accelerated oxidation rate and produced oxide scales different from those formed in air. These feature evolutions in surface oxide are expected to offer complementary insight on determining the fire characteristics, such as the exposure temperature, period and whether liquid accelerant is involved. 相似文献
4.
Failure analysis normally requires many forms of investigation, but visual examination is the most used amongst all possible techniques. However, as the legal climate for fire investigation is becoming more rigorous, fire researchers need to work differently. In other words, to be technically defensible, expert testimony must be built on scientific data. To this aim, in‐depth microstructural analyses of materials are particularly suitable to define the fire scene. This paper discusses some of the basic metallurgical theories used in failure analysis of copper, steel and aluminium alloy components involved in fire situations. Some components that can be easily found in fire and arson scene were submitted to simulated fire for indicated time and temperature. The collected samples were than examined by optical microscopy, scanning electron microscopy and energy‐dispersive spectroscopy. Oxidation, recrystallization, second‐phase precipitation and melting were some of the features observed on samples that can be strictly related to the thermal effect of fire. On the basis of these metallurgical results and starting from the evidence that different exposure temperatures can induce different metallurgical modifications, it is possible to define the temperature range experienced by various components, thus suggesting the fire dynamic during the incident. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
5.
In this paper, the authors present experimental results and observations of four full‐scale standard fire tests on single‐leaf steel doors and steel frames installed in 3 × 3 m non‐load‐bearing partition walls. Three full‐scale fire tests were performed on steel doors installed in lightweight partition walls constructed by using steel C‐section studs with gypsum boards fixed on both sides. Two lightweight walls incorporated Rockwool cavity insulation, while the third lightweight wall was constructed without cavity insulation. The fourth fire test involved a steel door installed in a masonry partition wall. While the steel door leaf and door frames were identical in all four full‐scale tests, only the steel door installed in the masonry wall achieved the desired fire resistance rating of 30 min. The integrity criterion for fire resistance was determined for the scenario when the door opened away from the furnace. The duration of fire resistance according to the integrity criterion was found to be 38, 25 and 19 min for the same door when installed in masonry wall, uninsulated lightweight wall and insulated lightweight wall respectively. For the thermal insulation criterion of fire resistance, the scenario of the door opening into the fire was found to be the most onerous. Copyright © 2016 John Wiley & Sons, Ltd. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
6.
7.
Steel‐framed houses using light‐gauge steel as a structural member have been developed and constructed since the early 2000s as a new construction pattern in the low‐rise construction market in Korea. Generally, the steel frames consist of two major load‐carrying elements such as load‐bearing wall and floor construction made up of approximately 1.0‐mm cold‐formed light‐gauge steel and light‐weight boards. Therefore, the steel frames are very simple to construct and make the construction period shorter than the ordinary construction type or concrete‐based construction. In Korea, regardless of the construction material types, the building regulation requires 1‐h fire rating for apartment buildings of four stories or under. To meet the fire resistance, new models of load‐bearing wall and floor should be developed. From the fire test results, two layer gypsum boards of 12.5 mm in thickness reinforced with glass fiber were proven satisfactory to provide 1‐h fire resistance with load‐bearing wall and floor. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
8.
Jadwiga Fangrat 《火与材料》2017,41(2):99-110
Non‐combustibility is discussed on the basis of experimental data for 66 commercial building materials obtained from two standard test methods: EN ISO 1716 oxygen bomb calorimeter and EN ISO 1182 cylindrical furnace. The sample materials are divided into five categories: concrete and ceramics, thermal/acoustic insulation materials, wall or ceiling boards, mortars and adhesives and thin coatings. To better distinguish between non‐combustible and combustible materials, an effective modified heat of combustion is defined and calculated for all materials tested in both methods. The materials studied exhibited very different mass loss values and a low tendency to auto‐ignite in the cylindrical furnace. Revised criteria for class A1 are proposed for better accuracy of reaction‐to‐fire assessment. It is proposed to use the oxygen bomb calorimeter with only one limit for the heat of combustion, that is, a value of 5 MJ/kg for all materials. The proposed approach is a very efficient tool for fast and inexpensive screening for non‐combustibility of building products and is expected to be a more precise method to distinguish between non‐combustible and combustible materials. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
9.
Among the commercial materials, stainless steel is widely used in our daily life and can be hardly destroyed by flame or the heat emanating from a fire. In this fundamental work, the formation and development of oxide scale on stainless steel 1Cr11Ni2W2MoV were investigated at 600°C to 800°C in the atmospheres with and without liquid accelerant. The aim of this work is to figure out the influence of accelerant on the oxidation pattern of stainless steel at high temperature that occurs in a fire. The morphology, microstructure, and the growth rate of the oxide scales were characterized by thermogravimetric analysis, visual analysis, scanning electron microscopy, energy‐dispersive spectroscopy, and X‐ray diffraction. The results revealed that the oxide scale formed on the stainless steel 1Cr11Ni2W2MoV was mostly protective in both atmospheres from 600°C to 800°C, except that breakaway oxidation occurred locally that resulted in the formation of intrusion oxide. Both increasing temperature and the presence of kerosene in combustion atmosphere increased the mass gain of stainless steel, which was mainly attributed to the occurrence of local breakaway oxidation. Consequently, the addition of accelerant just increased the formation trend of local intrusion oxide, rather than remarkably affect the scaling behavior. Therefore, careful analysis is needed to identify the presence possibility of accelerant in oxidation atmosphere according to the scaling behavior of stainless steel. Characterization of surface scale and metallurgical analysis of metallic material are expected to be supplementary technique for fire characterization in the future. 相似文献
10.
The ability to accurately identify fire patterns is the fundamental requirement for fire investigations. The corrosion layers of steel in fire scenes exhibit three distinct characteristics. First, due to steel's nonflammable nature, steel patterns can be preserved better at the fire site than patterns formed on other combustible materials; second, both the high temperature and the smoke during the fire affect the high-temperature oxidation process; and third, the corrosion layer of steels inevitably undergoes further evolution after the fire because of the subsequent room-temperature corrosion. This study focuses on investigating Q235 steel because of its extensive use in construction and vehicles. The pattern evolution processes of high-temperature oxidation at elevated temperatures in air, polyethylene (PE), and polyvinyl-chloride (PVC) combustion smoke and the corresponding subsequent corrosion at room temperature were systematically investigated from the perspective of macroscopic and microscopic morphology. The results showed that the smoke atmosphere played an important role in the formation of the corrosion layer of Q235 steel. Compared with samples oxidized in air, samples oxidized in PE combustion smoke exhibited a uniform and dense oxide layer on the surface, which inhibited the corrosion at room temperature further. The PVC combustion smoke accelerated the high-temperature oxidation of the sample, and its influence on the subsequent room-temperature oxidation process was closely correlated with the temperature of the high-temperature oxidation. The results of this study provide important references for understanding the formation of the corrosion layer of Q235 steel for fire investigations. 相似文献
11.
Hedieh Farhandi Md Nurul Karim Renato S. M. Almeida Kamen Tushtev Kurosch Rezwan 《Journal of the American Ceramic Society》2022,105(3):1928-1938
Adapting conventional sintering (CS) techniques of monolithic ceramics for the production of oxide ceramic matrix composites (Ox-CMCs) comes along with a few drawbacks, such as fiber degradation. Thus, the applicability of two-step sintering (TSS) for the production of Ox-CMCs based on Nextel™ 610 fibers and porous alumina matrix is investigated in this study for the first time. Uniaxial tensile tests were performed to evaluate the performance of mini-composites produced by TSS and compared with those produced by CS. Parameters known for influencing the mechanical behavior of the mini-composites, such as grain size, porosity, shrinkage, as well as matrix properties, were analyzed. Both sintering techniques resulted in similar grain size distributions, whereas TSS showed higher total porosity and lower amount of sintering-induced cracks. As a result, TSS samples showed a higher tensile strength of 230±27 MPa when compared to 133±8 MPa for CS. In general, it was observed that most of the densification happens during the first phase of TSS, while the matrix is slowly strengthened during the second step. Therefore, the reported TSS process is a very promising and easy-to-apply heat treatment for producing Ox-CMCs with controlled microstructure. 相似文献
12.
钢纤维改善混凝土力学性能和微观结构的研究 总被引：5，自引：0，他引：5
研究了水胶比为0.45,钢纤维掺量为0、0.5％、1.0％、1.5％和2.0％的五种混凝土的力学性能以及其水化28天后的微观形貌.结果表明:钢纤维对混凝土的抗压强度改善并不明显,当钢纤维掺量为1.5％时,混凝土的抗压强度仅比普通混凝土提高了7.4％;但钢纤维的掺入大大提高了混凝土的劈裂抗拉强度和抗折强度,当钢纤维掺量为1.5％时,混凝土劈裂抗拉强度提高了80％,当钢纤维掺量为2.0％时,混凝土抗拉强度提高了近一倍.混凝土的宏观力学性能特征与微观结构分析结果相吻合. 相似文献
13.
Estève Ernault Julie Diani Simon Hallais Clio Cocquet 《Polymer Engineering and Science》2021,61(7):1971-1981
The mechanical behaviors of five polyether block amide foams, obtained by mold-opening foam injection process, were investigated with regard to their microstructures. The materials vary in mass ratios of hard versus soft segments, and/or in process packing time. The resulting microstructures have been characterized in terms of cavity size and shape ratios, by analyzing scanning electron microscope images after careful sample preparation. The foam mechanical responses have been characterized in compression at small and large strain. At small strain, the initial linear part of the stress–strain curve is enhanced firstly by the hard segment mass ratio and secondly by the fineness of the microstructure. Similar results have been obtained at large strain. The foam viscoelasticity at large strain has been characterized by stress relaxation and strain recovery tests, relevant for foam applications. Reduced packing time and pressure have been shown to lead to the presence of undesired large cavities. The morphological defects appear to have a negligible impact on the macroscopic mechanical behavior of the foams at infinitesimal strain, but lead to critical inconsistency at large strain. Furthermore, the mechanical behavior of the tested polyether block amide foams is controlled first by hard versus soft segments ratio, and second by the microstructure fineness. 相似文献
14.
Behnam Salmany Kozekanan Alireza Moradkhani Hamidreza Baharvandi Naser Ehsani 《International Journal of Applied Ceramic Technology》2021,18(3):957-971
In this research, carbon sources (Resin Phenolic, Carbon Black and Graphite) and Boron Carbide (B4C) were used to improve the mechanical properties of Silicon Carbide (SiC) composite. For this purpose, carbon sources of 0.5, 0.75, 1, 1.5, 2, 2.5, 3, and 5 wt% as well as 0.5 wt% B4C were added to SiC powder, respectively. The sample containing SiC—2.5 wt% Resin Phenolic—0.5 wt% B4C had the best properties with relative density, hardness, and fracture toughness values of 98.5%, 2820 GPa, and 3.9 MPa.√m, respectively. Examination of SEM images showed that by increasing carbon from 0.5 to 2.5 wt%, the fracture changes from intergranular to transgranular. 相似文献
15.
Fire investigations aim to establish the origin and cause of fires by collecting and analyzing the comprehensive fire‐related evidences. Metallic materials exposed to the fire scene environments are usually subjected to melting and/or high‐temperature oxidation, and they have been considered vital parameters for temperature determination, as recommended in NFPA 921. The oxide characteristics obtained from the conventional fire investigations primarily rely on simple visual observations such as the variations in oxide color, the so‐called “oxidation patterns.” However, such information is not sufficiently convincing due to the complex nature of oxides formed in the fire scene. The oxide color is strongly affected by the type of oxide, the oxide thickness, the concentration of contaminant, and the interactions among different oxides. In this study, Q235 structural steel samples have been exposed to high‐temperature air and simulated kerosene combustion conditions at certain temperatures and for indicated periods. The oxidation rate was examined by thermogravimetric analysis. The morphologies and microstructures of the oxide scales were investigated by scanning electron microscopy, energy dispersive spectroscopy, and X‐ray diffractions. The results show that the oxide properties are strongly dependent on the oxidation temperature and oxidation atmospheres. These oxidation behaviors are expected to provide useful information on identifying fire characteristics. 相似文献
16.
本文研究了反应烧结含ZrO_2的刚玉-莫来石材料及其碳结合材料的相组成,显微结构和力学性能。结果表明,对刚玉-莫来石材料由于加入氧化锆引起的微裂纹,中、低温强度趋于下降;但在1300℃以上,强度和抗蠕变性能都有明显上升。这可能是因为微裂纹得到一定弥合,同时氧化锆和莫来石之间形成晶界固溶。对碳结合刚玉-莫来石-氧化锆材料,在所有试验温度下,强度都随石墨加入量增加而下降。强度-温度曲线呈现两个特征:(1)由600℃至800℃强度下降,而由800℃至1000℃强度均有回升;(2)由1300℃至1400℃强度略有回升。这与金属粉添加剂在不同温度下的行为有密切关系。形成针状或纤维状的碳化物有利于提高强度。 相似文献
17.
氮化硼对锆刚玉莫来石材料力学性能及显微结构的影响 总被引：1，自引：1，他引：1
研究了锆刚玉米莫来石－氮化硼复合材料的显微结构及力学性能，结果表明，在锆刚玉莫来基质引入氮化硼，降低材料的抗折强度，但可提高断裂韧性。这是氮化硼的微裂纹增韧作用所致。氮化硼的编织状结构可阻碍晶界的滑移，降低材料高温强度的衰减率。材料内生成的针状９Ａｌ２Ｏ３．２Ｂ２Ｏ３，在断裂过程生产拔出效应，有利于力学性能的提高。 相似文献
18.
Q. An K. Y. Fan Y. F. Ge Y. C. Liu S. Wang 《Journal of Adhesion Science and Technology》2020,34(6):670-685
AbstractThis paper investigated the microstructure and mechanical properties of Q235/304 stainless steel clad plate welding seam produced by hybrid welding of tungsten inert gas welding (TIG) and metal active gas arc welding (MAG). The results showed that the dual phases containing ferrite and austenite appeared in the stainless steel covering welding (SSCW), while the partial martensite phases appeared in the carbon steel backing welding (CSBW), which is attributed to the dilution behavior of Ni and Cr elements from stainless steel to the Q235 steel results into the movement of the CCT curve to the right side and the decrease of critical martensite formation cooling rate. The CSBW possesses the highest microhardness value in the weld metal due to the existence of the martensite zone. The impact tests were carried out and the results showed that the Charpy absorbed energy of weldments (81?J) is almost equal to that of base clad plate (83?J). The SSCW layer possesses the ductile fracture characteristics accompanying many dimples. However, in the CSBW layer, some cleavage fracture characteristics are presented in the radiation zone while many dimples are located in the fibrous zone, revealing a complex combination of brittle and ductile fracture behavior, which is due to the existence of martensite zone, different stress states and crack propagation velocity.
- Highlights
Hybrid (TIG, MAG) welding is suitable for welding stainless steel clad plate;
The martensite formation in CSBW is related to dilution and diffusion of Cr and Ni;
Partial martensite transformation can strengthen and toughen the welding seam.
19.
Shuqi Guo 《Journal of the American Ceramic Society》2019,102(6):3286-3295
In this study, a homogenously dispersed finer SiC particles-containing ZrB2 composite was prepared using nanosized polycarbosilane (PCS) particles-containing ZrB2 mixture powder, followed by hot pressing. The microstructure of the resulting composite was characterized by field-emission scanning electron microscopy and transmission electron microscopy. The composite microstructure comprised finer equiaxed ZrB2 and SiC grains. The mechanical behavior of the composite was evaluated using four-point bending test at different temperatures between room temperature (RT) and 1600°C. The results show that the composite exhibited only linear deformation behavior prior fracture at or below 1500°C. However, a trace quantity of nonlinear deformation was observed at 1600°C. In addition, the flexural strength of the composite decreased as the temperature increased from RT to 1200°C, then the strength increased as the temperature raised to 1400°C. Subsequently, the flexural strength remained almost the constant between 1400°C and 1600°C, with a strength of ~760 MPa. 相似文献
20.
Currently, rural fire protection issues in China loom large, resulting in frequent fire incidents due to an inadequate rural fire infrastructure and insufficient firefighting resources. Consequently, prompt fire suppression becomes challenging, leading to significant casualties and economic losses. To address these challenges and align with the national rural revitalization strategy, our research team dedicated 5 years to meticulously scrutinizing fire incident data in China spanning from 2012 to 2022, alongside an extensive review of international documents. We conducted on-site investigations in rural areas across 63 cities in 11 provinces, including Anhui and Jiangsu. By analyzing fire data and field investigation results, we identified the causes and percentages of 11 types of rural fires, as well as summarized five types of rural fire hazards and six types of rural fires. Drawing from insights gleaned from the experiences of countries such as the United States, Australia, Canada, and South America, we have formulated eight policy recommendations for rural fire protection, encompassing aspects like organization, responsibility, planning, construction, operation, and maintenance, as well as public awareness. Therefore, we anticipate that this study will catalyze enhancing rural fire protection efforts in China and other developing nations. 相似文献