近年来，我国电气火灾形势严峻，电气故障仍是引发火灾的首要原因。火灾物证鉴定是火灾调查工作中一种重要的技术手段和方法，对查明火灾原因，预防火灾再发生有至关重要的作用。本文立足当前电气火灾物证鉴定存在的不足，针对部分电气火灾物证仍难以给定准确原因，利用电气故障模拟实验装置模拟短路故障，汽油喷灯模拟高温火烧条件，开展短路及火烧实验，重点研究了短路与火烧熔痕痕迹典型特征，主要集中在绝缘层、熔痕、线芯等方面，补充火灾物证鉴定证据链，总结短路与火烧熔痕鉴定依据，进一步提高火灾调查的准确性和科学性。
  利用红外热像仪和高速摄像机记录实验过程，逐帧分析导线发生短路故障时变化情况。研究结果表明，2.5 mm² ZR-BV单芯铜导线短路条件下依次发生绝缘层发烟、熔化、鼓包、炭化、弯曲、燃弧、金属喷溅、明火燃烧、滴落变化；绝缘导线熔断电流为130 A，熔断时间93 s，电流大于140 A均能熔断，绝缘熔融滴落起始电流157.5 A，裸导线起始熔断电流和时间均小于绝缘导线。
  采用体视显微镜和扫描电镜-能谱仪，对短路及火烧条件下绝缘层与熔痕痕迹微观形貌和元素分析，结果发现，不同条件下绝缘层表面析出晶粒结构位置不同；一次短路熔痕表面有金属光泽，分布细小火山口状孔洞或缩孔，线芯有结疤痕和球形凸起，二次短路熔痕表面光泽度差，孔洞和缩孔较多，线芯凸起以球形为主，火烧熔痕表面有大量多边形固溶体和碳颗粒，线芯上有熔化变细区，无孔洞；不同条件下熔痕元素种类相似，可根据元素含量差异鉴定熔痕成因。
  使用金相显微镜，采用Image-Pro-Plus软件对短路及火烧熔痕微观组织分析，结果表明，一次短路熔痕晶粒细小，平均直径13.14~17.87 μm，以枝晶为主，晶界较细，枝晶方向明显，有激冷层结构；气孔较少，体积较小，形状较规则。二次短路熔痕晶粒以胞状晶、柱状晶为主，平均直径15.72~22.30 μm，晶粒稀疏，晶界粗大，晶界偏析明显；气孔较多，体积较大，形状不规则。火烧熔痕晶粒类型粗大等轴晶为主，熔痕仅在表层分布有细小气孔或缩孔，内部几乎没有气孔与缩孔。
 

  In recent years, the form of electrical fires in China has been severe, and electrical faults are still the primary cause of fires. Fire material evidence identification is an important technical means and method in fire investigation, which plays a vital role in identifying the cause of fire and preventing the recurrence of fire. Based on the shortcomings of the current electrical fire evidence identification, this paper uses the electrical fault simulation experimental device to simulate the short circuit fault, the gasoline burner simulates the high temperature fire condition, and carries out the short circuit and fire experiments, focusing on the short circuit. The typical characteristics of fire and fusion marks are mainly concentrated in the insulation layer, fusion marks, wire cores, etc., supplement the evidence chain of fire physical evidence identification, summarize the identification basis of short circuit and fire fusion marks, and further improve the accuracy and scientificity of fire investigation.
  An infrared thermal imager and a high-speed camera were used to record the experimental process, and the changes in the short-circuit fault of the wire were analyzed frame by frame. The research results show that under the short-circuit condition of the 2.5 mm2ZR-BV single-core copper wire, the insulation layer smokes, melts, bulges, carbonization, bending, arcing, metal splashing, open flame burning, and dripping changes; the fuse current of the insulated wire is 130 A, the fusing time is 93 s, and the current is greater than 140 A. The initial current of insulation melting and dripping is 157.5 A. The initial fusing current and time of the bare wire are smaller than that of the insulated wire.
  Stereo microscope and scanning electron microscope-energy dispersive spectrometer were used to analyze the micro-morphology and elemental analysis of the insulating layer and the melting marks under short-circuit and fire conditions. The results showed that the grain structure of the insulating layer appeared at different positions under different conditions; The surface has metallic luster, with small crater-like holes or shrinkage holes, the core has knot scars and spherical protrusions, the surface gloss of the secondary short-circuit melting marks is poor, there are many holes and shrinkage holes, and the core protrusions are mainly spherical. , there are a large number of polygonal solid solutions and carbon particles on the surface of the burnt melt mark, and there is a melting and thinning area on the wire core without holes; the types of melt mark elements are similar under different conditions, and the cause of the melt mark can be identified according to the difference in element content.
  Microstructure analysis of short-circuit and fire-melt traces using a metallographic microscope and Image-Pro-Plus software, and the results showed that the grains of the primary short-circuit marks were fine, with an average diameter of 13.14~17.87 μm, mainly dendrites, fine grain boundaries, and obvious dendrite directions. Chilled layer structure; fewer pores, smaller volume and more regular shape. The grains of the secondary short-circuit melting marks are mainly cellular and columnar, with an average diameter of 15.72~22.30 μm. The grains are sparse, the grain boundaries are coarse, and the grain boundary segregation is obvious. The grain type of the burnt melt marks is mainly coarse and equiaxed grains. The melt marks are only distributed with small pores or shrinkage holes on the surface, and there are almost no pores and shrinkage holes inside.

 

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