To explore a potential method for improving the toughness of a polylactide (PLA), we used a thermoplastic polyurethane (TPU) elastomer with a high strength and toughness and biocompatibility to prepare PLA/TPU blends suitable for a wide range of applications of PLA as general-purpose plastics. The structure and properties of the PLA/TPU blends were studied in terms of the mechanical and morphological properties. The results indicate that an obvious yield and neck formation was observed for the PLA/TPU blends; this indicated the transition of PLA from brittle fracture to ductile fracture. The elongation at break and notched impact strength for the PLA/20 wt %TPU blend reached 350% and 25 KJ/m 2 , respectively, without an obvious drop in the tensile strength. The blends were partially miscible systems because of the hydrogen bonding between the molecules of PLA and TPU. Spherical particles of TPU dispersed homogeneously in the PLA matrix, and the fracture surface presented much roughness. With increasing TPU content, the blends exhibited increasing tough failure. The Jintegral value of the PLA/TPU blend was much higher than that of the neat PLA; this indicated that the toughened blends had increasing crack initiation resistance and crack propagation resistance.

No abstract

No abstract

No abstract

No abstract

Stoppers are commonly used to improve the shock resistance of MEMS devices. However, the collision between MEMS structure and stoppers in shock environment may lead to emergence of the stress wave, resulting in the failure of devices. Therefore, MEMS devices designed based on current statics theory is unreliable. After analyzing the method and principle for MEMS reliability design, the shock dynamics model was established. Based on the model, the response of the traditional design and designs with different stoppers to shock was researched. At last, protection performances of different stoppers were evaluated. Results showed that the use of stoppers could improve the shock resistance of the device obviously, but hard stoppers would cause to the emergence of the sharp stress wave. Elastic stoppers had excellent protection ability which could strengthen the shock resistance of the device greatly.

To study the dynamic characteristic of a vibration compaction system, we first build up a double DOF model, then it is solved with transfer matrix method and the mathematical description was carried through on the status of every units in the model. Through the analysis of simulation data with simulation software, the data with the transfer matrix equation is the same as data with simulation software. This made clear that the transfer matrix model approaches to the practical circumstances and it bears important referencing value to the dynamics analysis of the correlation system.

With the qualities of smooth operation, high efficiency and small size, the planetary gear box was widely used in transmission field. In this paper, a 2-stage planetary gear box was studied. CAXA and Pro/E were used for modeling. The FEA analysis results were obtained by ANSYS, both the contact stress and the bending stress of the gear tooth root. The results showed that with the continuous action of cyclic loads, the excessive contact stress is the direct reason of the failure. Then, the system reliability evaluation was made, which can provide guidance for engineering practice.