This study quantifies the relationship between acoustic emission (AE) and stiffness loss in the fused-filament microstructure of additively manufactured objects, considering the effect of tensile force direction as strain increases. We correlate the continuous decrease in tangent Young’s modulus with the rate of detected AE signals using uniaxial tensile tests. The results reveal a highly significant correlation between the number of detected acoustic emission signals and the decrease in tangent Young’s modulus, demonstrating that the detected acoustic emission events can be employed to numerically predict the reduction in stiffness with increasing strain.