Zorc Borut, Zorc Matija, Kosec Borut, Nagode Aleš
Welding Institute Ltd., Ptujska 19, SI-1000 Ljubljana, Slovenia.
Faculty of Natural Sciences and Engineering, University of Ljubljana, Aškerčeva 12, SI-1000 Ljubljana, Slovenia.
Polymers (Basel). 2020 Jan 31;12(2):280. doi: 10.3390/polym12020280.
A destructive pressure test of styrene-acrylonitrile (SAN) water-filter housings showed the influence of the shape and specific details of the housings on their critical areas and their destructive pressure. The destructive pressure varies by as much as 37 bar due to different dominant stresses in the individual types of housings. In critical areas of the housings, geometrical stress concentrators generally exist. For this reason, the stress caused by the internal pressure is locally 2.75-3.4 times greater than that expected based on the water pressure, which means that cracks are initiated in these places. However, the bottom of the housings can be in a form such that the maximum stress and the crack originates in its central part without the influence of local stress concentrators. The tensile strength of the SAN is theoretically estimated at 73 N/mm, which is comparable with the literature data. The fracture toughness of the SAN is typically low, theoretically estimated in the range 1.45-3.55 MPa·m, and strongly depends on the degree of the wall's stress-increasing rate or the crack-propagation rate. Therefore, at various crack-propagation rates, the critical crack depths are also different, in the range 100-600 μm. Due to this, the critical thickness for brittle fracture in the SAN is also different; it is ten times greater than the critical crack length. The characteristic of a sub-critical crack, i.e., the mirror zone, is its macroscopically smooth surface, which is microscopically very finely roughened. In the case of a sufficiently slowly growing sub-critical crack, the surface of the mirror zone contains characteristic parabolic markings. The over-critical, sufficiently rapidly growing cracks generally grow mainly in the plane-strain state and only the final thin layer of the remaining wall thickness breaks in the plane-stress state. The over-critical, sufficiently slowly growing cracks grow in the plane-stress state with a strong shear plastic tearing.
苯乙烯 - 丙烯腈（SAN）滤水器外壳的破坏性压力测试显示了外壳的形状和特定细节对其关键区域及破坏压力的影响。由于不同类型外壳中存在不同的主导应力，破坏压力变化高达37巴。在外壳的关键区域，通常存在几何应力集中器。因此，内部压力引起的应力在局部比基于水压预期的应力大2.75 - 3.4倍，这意味着在这些地方会产生裂纹。然而，外壳底部可以采用这样一种形式，即最大应力和裂纹起源于其中心部分，而不受局部应力集中器的影响。理论上估计SAN的拉伸强度为73 N/mm，这与文献数据相当。SAN的断裂韧性通常较低，理论估计值在1.45 - 3.55 MPa·m范围内，并且强烈依赖于壁的应力增加率或裂纹扩展率。因此，在不同的裂纹扩展率下，临界裂纹深度也不同，范围在100 - 600μm。据此，SAN中脆性断裂的临界厚度也不同；它比临界裂纹长度大十倍。亚临界裂纹的特征，即镜面区，是其宏观上光滑的表面，微观上非常精细地粗糙化。在亚临界裂纹生长足够缓慢的情况下，镜面区的表面包含特征性的抛物线形标记。超临界、生长足够快的裂纹通常主要在平面应变状态下生长，只有剩余壁厚的最后一层薄区域在平面应力状态下断裂。超临界、生长足够慢的裂纹在平面应力状态下生长，伴有强烈的剪切塑性撕裂。
