无损检测缺陷分析课件

,Chapter 2 Defect Analysis,本章提要： 缺陷分析是无损检测的技术基础。 主要解决两方面的问题： 一是弄清defects classification、 property and harmfulness； 二是分析the causes of defects，以便有效地Identify defects and eliminate defects，提高工艺质量。 本章重点讲授defects classification and harmfulness。缺陷的产生原因应结合材料成型原理课程内容深入理解与总结。 最后，对Commonly used detection methods作简要介绍。,2.1 Concept and classification of process defects,2.1.1 Concept of process defects （1） What are the process defects？ 在材料加工成型过程中，经常会出现 某种或某些不合乎质量要求的appearance defect, property defect and organization defect和更为严重的internal geometric defect（如cracks、 pores、inclusions等）。我们把这些“metallurgical factors 、 structural factors and technological factors”导致的产品质量不符合相关参考标准的各类缺陷统称为工艺缺陷。,（2）Dialectical analysis of process defects The absoluteness of defect generationIn actual production, the acquirement of the products without any defects is quite difficult； It is not economical or even impossible to make the products produced in batches without any defects. The relativity of defect evaluation standardsThe relativity of waste standards. As for the same of various parts, the quality requirements are different due to the different working conditions. Therefore, the waste standards are also different., Formulation principle of waste standards： Generally speaking, the higher the product quality level is, the greater the risk after failure will be, and the control of defects should be more strict. Therefore, It is necessary to pay attention to the implementation and reference to the relevant standards, which is also called the principle of fitness for purpose., Repair of process defects： Minor defect that do not affect the application can be tolerated. Serious defect that do not meet the requirements must be treated. Some defects can be repaired in time, and some defects may not be repaired which must be sentenced to waste.,Examples,比如： Excessive reinforcement，属于焊缝形状不良，严重时可以Grinding；必要时grinded the reinforcement smooth。 再如：sand inclusion on the surface of casting，可以通过repair welding来修复。 特别指出，考虑到焊接接头组织和性能的恶化，某些产品的welding repair不允许超过2次！所以，应该注意formulate a rigorous repair process ，否则就会造成Economic loss！,2.1.2 Classification of process defects 工艺缺陷种类繁多，产生原因也相当复杂。为了便于分析和处理工艺缺陷、制定检验工艺、方便技术交流，有必要对其进行分类。 (1)按technical connotation大体分为： Manufacturing and assembly defects如焊件groove angle、assembling gap不均匀，unfitness过大等； Shape and size defects如deformation 、inconformity of the width of bead、Excessive reinforcement、collapse、spill-over、overlap等等；, Geometric discontinuous defect 如焊件中的裂纹、孔洞、夹杂、未熔合、未焊透，铸件中的缩孔、疏松、裂纹等等； Microstructure and performance defect如机械性能不良、耐腐蚀性下降、过热组织、脆性组织、偏析等等； Other process defects 如spatter 、scratch on surface、arc scratch、gouge、grinding defect,（2）按process technique分为: Welding defect因实施焊接工艺而引起的缺陷； Casting defect因实施铸造工艺而引起的缺陷； Forging defect因实施锻造、冲压工艺而引起的缺陷； Heat treatment defect （略）,（3）按Defect property不同分为： Crack如冷裂纹、热裂纹、再热裂纹、 层状撕裂、火口裂纹等； Hole如缩孔、气孔等； Solid inclusion如夹渣、夹钨等； Faulty fusion如坡口未熔合、层间未熔合； Incomplete fusion如根部未焊透、中部未焊透； Other defects未包含在以上5种缺陷中的缺陷，如undercut、burnthrough、weld beading、arc scratch.,（4）按buried depth of defects分为： Surface defect如表面气孔、表面裂纹、砂眼、咬边等； Near surface defect如皮下气孔、夹杂等； Internal defect如内部夹杂、气孔、缩孔、裂纹、未熔合、未焊透等； (5)按缺陷的geometrical characteristic不同分为： volumetric defect 如孔洞、夹杂等； area type defect如裂纹、未熔合、夹层等；,（6）按具体缺陷的position feature又有不同的称谓：例如： 裂纹可分为：HAZ crack、weld crack 、 crater crack、toe crack、root crack； 未熔合可分为： groove incomplete fusion、 incomplete fusion between layers、root department incomplete fusion （7）其它分类： According to different tendencies：transverse crack、longitudinal crack、chevron crack、 radiate crack； According to different sizes ：macro crack、micro crack,According to the mechanism of defect production, there are different classifications, such as： The cracks in welded joints： hot crack、cold crack、reheat crack 、lamellar tearing； The porosity in welded joint： hydrogen porosity、nitrogen porosity 、 carbon monoxide porosity,Crack defects(必须避免),Faulty fusion defects,熔化焊时，在焊缝金属与母材之间或焊道金属之间未能完全熔化结合而留下的缝隙。有侧壁、层间和根本未熔合等。 危害：面状缺陷，易造成应力集中，危害性大，不允许。,产生原因：层间和坡口侧壁渣清理不干净；焊接电流偏小；焊条偏离坡口侧壁距离太大；焊条摆动幅