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NUMERICAL EVALUATION OF MODE I STRESS INTENSITY FACTOR AS A FUNCTION OF MATERIAL ORIENTATION FOR BX-265 FOAM INSULATION MATERIAL

机译：MOTE强度因子作为BX-265泡沫绝缘材料材料取向函数的数值评估

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Foam, a cellular material, is found all around us. Bone and cork are examples of biological cell materials. Many forms of man-made foam have found practical applications as insulating materials. NASA uses the BX-265 foam insulation material on the external tank (ET) for the Space Shuttle. This is a type of Spray-on Foam Insulation (SOFI), similar to the material used to insulate attics in residential construction. This foam material is a good insulator and is very lightweight, making it suitable for space applications. Breakup of segments of this foam insulation on the shuttle ET impacting the shuttle thermal protection tiles during liftoff is believed to have caused the space shuttle Columbia failure during re-entry. NASA engineers are very interested in understanding the processes that govern the breakup/fracture of this complex material from the shuttle ET. The foam is anisotropic in nature and the required stress and fracture mechanics analysis must include the effects of the direction dependence on material properties. Material testing at NASA MSFC has indicated that the foam can be modeled as a transversely isotropic material. As a first step toward understanding the fracture mechanics of this material, we present a general theoretical and numerical framework for computing stress intensity factors (SIFs), under mixed-mode loading conditions, taking into account the material anisotropy. We present mode I SIFs for middle tension -M (T) - test specimens, using 3D finite element stress analysis (ANSYS) and FRANC3D fracture analysis software, developed by the Cornell Fracture Group. Mode I SIF values are presented for a range of foam material orientations. Also, NASA has recorded the failure load for various M (T) specimens. For a linear analysis, the mode I SIF will scale with the far-field load. This allows us to numerically estimate the mode I fracture toughness for this material. The results represent a quantitative basis for evaluating the strength and fracture properties of anisotropic foam insulation material.
机译：泡沫，一种细胞材料，都在我们周围发现。骨和软木是生物细胞材料的例子。许多形式的人造泡沫已发现实际应用作为绝缘材料。美国宇航局使用外部罐（ET）的BX-265泡沫绝缘材料进行航天飞机。这是一种喷涂泡沫绝缘（SOFI），类似于用于隔离住宅结构中阁楼的材料。这种泡沫材料是一种很好的绝缘体，非常重量轻，适用于空间应用。据信，这种泡沫保温件的分裂，影响在剥离过程中施用穿梭热保护瓦片的速度，因此在重新进入期间导致航天飞机哥伦比亚失败。美国宇航局工程师非常有兴趣了解管理该复杂材料的分解/骨折从梭子等的过程。泡沫本质上是各向异性的，并且所需的应力和断裂力学分析必须包括方向依赖性对材料特性的影响。 NASA MSFC的材料测试表明，泡沫可以作为横向各向同性材料进行建模。作为理解这种材料的断裂力学的第一步，我们在混合模式的负载条件下，给出了用于计算应力强度因子（SIFS）的一般理论和数值框架，考虑到材料各向异性。我们以康奈尔骨折组开发的3D有限元应力分析（ANSYS）和FRAND3D骨折分析软件，呈现MODE IIFS - TEST-M（T） - 测试标本。模式I SIF值显示为一系列泡沫材料方向。此外，美国宇航局已经记录了各种M（T）样本的故障负载。对于线性分析，模式I SIF将与远场负载扩展。这允许我们在数值上估计该材料的裂缝韧性的模式。结果表示评估各向异性泡沫绝缘材料的强度和断裂性能的定量依据。

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