Space charge measurements according to the pulsed electroacoustic (PEA) method are performed in disc samples of epoxy at electric fields from about 2 to 20 kV/mm and at temperatures of 25 and 40 °C. The accumulation of homo-charges and hetero-charges in the epoxy samples is found under DC stress. Both homo- and hetero-charges form stable space charge zones. The accumulation of space charges is influenced by a surface layer of the samples, probably caused by casting and oxidation. If the surface layer is removed, no hetero-charge accumulation is observed. Further, the injected homo-charges do not form a stable space charge region in front of the electrode, but travel further into the material, forming an initial wave-front-like charge distribution. A charge transport model is developed taking into account charge injection, charge accumulation and charge transport. The charge transport model is validated by the space charge measurements.

中文翻译：

---

直流应力下表面层对环氧样品空间电荷积累的影响

根据脉冲电声 (PEA) 方法，在约 2 至 20 kV/mm 的电场和 25 和 40 °C 的温度下，在环氧树脂圆盘样品中进行空间电荷测量。在直流应力下发现环氧树脂样品中同电荷和异电荷的积累。同电荷和异电荷都形成稳定的空间电荷区。空间电荷的积累受样品表面层的影响，可能由铸造和氧化引起。如果去除表面层，则不会观察到异电荷积累。此外，注入的同质电荷不会在电极前形成稳定的空间电荷区，而是进一步进入材料，形成初始波前状电荷分布。考虑到电荷注入，开发了电荷传输模型，电荷积累和电荷传输。电荷输运模型通过空间电荷测量得到验证。