Envelopes are main structures of stratospheric airships. They are usually made of laminated fabrics and prone to tearing, so it is significant to study their tear strengths. This paper aims to investigate the tear strength of an envelope for stratospheric airships by uniaxial and biaxial tear tests. Three uniaxial tear specimens and 15 biaxial tear specimens under five different stress ratios (warp stress vs weft stress) were tested, and their tear strengths were measured. Two-dimensional digital speckle correlation method was used to obtain specimens’ strain contours. The test results show that the average tear strength of uniaxial specimens is 32.99 N/mm, over 20% higher than those of biaxial specimens, ranging from 25.50 N/mm to 27.25 N/mm. It reveals that weft stress reduces the tear strength; nevertheless, the stress ratios slightly affect the tear strength. Besides, the strain contours clearly show three zones in each specimen – the low-strain zone, the high-strain zone, and the medium-strain zone. Depending on the strain contours and previous research on imperfect composite materials, we inferred that the crack-tip stress concentration factor of a uniaxial specimen is lower than that of a biaxial specimen. It explains the difference in tear strength between uniaxial and biaxial specimens. These findings suggest using biaxial tear test to measure the tear strength of an SSA’s envelope.

信封是平流层飞艇的主要结构。它们通常由层压织物制成，容易撕裂，因此研究其撕裂强度非常重要。本文旨在通过单轴和双轴撕裂试验研究平流层飞艇外壳的撕裂强度。在五个不同的应力比（经向应力与纬向应力）下测试了三个单轴撕裂试样和15个双轴撕裂试样，并测量了它们的撕裂强度。使用二维数字散斑相关方法获得标本的应变轮廓。测试结果表明，单轴试样的平均撕裂强度为32.99 N / mm，比双轴试样的平均撕裂强度高25％（从25.50 N / mm到27.25 N / mm）。它表明纬线应力会降低撕裂强度。尽管如此，应力比会稍微影响撕裂强度。此外，应变轮廓清楚地显示了每个样本中的三个区域-低应变区域，高应变区域和中应变区域。根据应变轮廓和对不完善复合材料的先前研究，我们推断单轴试样的裂纹尖端应力集中系数低于双轴试样。它解释了单轴和双轴试样在撕裂强度上的差异。这些发现建议使用双轴撕裂试验来测量SSA信封的撕裂强度。我们推断，单轴试样的裂纹尖端应力集中系数低于双轴试样。它解释了单轴和双轴试样在撕裂强度上的差异。这些发现建议使用双轴撕裂试验来测量SSA信封的撕裂强度。我们推断，单轴试样的裂纹尖端应力集中系数低于双轴试样。它解释了单轴和双轴试样在撕裂强度上的差异。这些发现建议使用双轴撕裂试验来测量SSA信封的撕裂强度。