Abstract Composites of polylactide (PLA) and polyformaldehyde (POM) were employed as the interposed sheet (IPS) to weld the dissimilar materials PLA and POM, utilizing ultrasonic thermal welding by the third phase (TWTP). PLA/POM composites showed excellent plasticity and retained the thermodynamic properties of the matrices, which are requirements of the IPS. The welded strengths were enhanced when the welding times and pressures increased, although extremely long welding times or extremely high pressures resulted in excessive heat, causing defects and decreasing the welded strengths. A maximum welded strength of 52 MPa was measured for the welded specimen, which was similar to the tensile strength of the PLA/POM composite when the welding time and pressure were 4 s and 0.2 MPa, respectively. Thus, the mechanical properties of both the matrices and IPS gave affects to the welded strength due to ultrasonic TWTP. Moreover, according to the polarizing microscopy images and the functional groups in the Fourier transform infrared (FTIR) spectra, gradient interfaces were observed and the thicknesses of the weld lines were identified as 40〜50 μm.

中文翻译：

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第三阶段超声热焊异种材料界面研究

摘要 采用聚乳酸（PLA）和聚甲醛（POM）的复合材料作为中间片（IPS），利用第三相（TWTP）超声热焊焊接异种材料PLA和POM。PLA/POM 复合材料显示出优异的塑性并保留了基体的热力学性能，这是 IPS 的要求。随着焊接次数和压力的增加，焊接强度提高，但焊接时间过长或压力过高会导致过热，产生缺陷，降低焊接强度。焊接试样的最大焊接强度为 52 MPa，这与 PLA/POM 复合材料在焊接时间和压力分别为 4 s 和 0.2 MPa 时的拉伸强度相似。因此，由于超声波 TWTP，基体和 IPS 的机械性能都会影响焊接强度。此外，根据偏光显微图像和傅里叶变换红外（FTIR）光谱中的官能团，观察到梯度界面，并确定熔接线的厚度为40〜50μm。