Increasing application scenarios of fiber reinforced composites pose more requirements for methodology of evaluating the material characteristics. Conventional 3-point-bending testing standards ISO 14,125 and ASTM 790 require a span-to-thickness ratio (STR) ≥ 16 for measuring the flexural modulus of fiber reinforced composite due to the influence of shear deformation. This study aims to relax the limitations of STR for accurately measuring the flexural modulus of fiber reinforced composite. Thus, the influences of shear deflection and local indentation deformation (LID) on measuring flexural modulus were investigated with numerical experiments. Moreover, two methods were developed and validated numerically and experimentally. The first method included polishing the specimens to various thickness followed by measuring the apparent flexural modulus of the specimens for each thickness and then fitting the flexural modulus with Timoshenko beam theory. The second method included reducing the unexpected influence of shear deformation and LID from the overall deflection with in-plane bending tests. The proposed methods can be used to accurately measure the flexural modulus of chopped fiber tape reinforced thermoplastic based on short beams with STR ≥ 7.5 and provide more flexibility in determining geometric size of the specimens for evaluating the flexural modulus of materials.

越来越多的纤维增强复合材料的应用场景对评估材料特性的方法提出了更多要求。由于剪切变形的影响，传统的 3 点弯曲测试标准 ISO 14,125 和 ASTM 790 要求跨厚比 (STR) ≥ 16 来测量纤维增强复合材料的弯曲模量。本研究旨在放宽 STR 在准确测量纤维增强复合材料的弯曲模量方面的局限性。因此，通过数值实验研究了剪切变形和局部压痕变形（LID）对弯曲模量测量的影响。此外，还开发了两种方法，并通过数值和实验进行了验证。第一种方法包括将试样抛光至不同厚度，然后测量每种厚度试样的表观弯曲模量，然后用 Timoshenko 梁理论拟合弯曲模量。第二种方法包括通过面内弯曲测试减少剪切变形和 LID 的意外影响。所提出的方法可用于准确测量基于 STR ≥ 7.5 的短梁的短切纤维带增强热塑性塑料的弯曲模量，并在确定试样的几何尺寸以评估材料的弯曲模量时提供更大的灵活性。第二种方法包括通过面内弯曲测试减少剪切变形和 LID 的意外影响。所提出的方法可用于准确测量基于 STR ≥ 7.5 的短梁的短切纤维带增强热塑性塑料的弯曲模量，并在确定试样的几何尺寸以评估材料的弯曲模量时提供更大的灵活性。第二种方法包括通过面内弯曲测试减少剪切变形和 LID 的意外影响。所提出的方法可用于准确测量基于 STR ≥ 7.5 的短梁的短切纤维带增强热塑性塑料的弯曲模量，并在确定试样的几何尺寸以评估材料的弯曲模量时提供更大的灵活性。