The effect of the properties of the polymer materials, such as molecular weight, molten viscosity, crystallization rate and the particle size of the powder, on the quality of selective laser sintering (SLS) parts is researched. The results indicate that the molecular weight affects the quality of the SLS parts through the melting viscosity. SLS parts of higher density can be fabricated with polymer materials of lower melting viscosity. Crystallinity largely affects the precision of the SLS part-shrinkage is more serious with increasing crystallinity. SLS parts sintered with polymer powder materials, whose melting peak and crystalline peak differ greatly, have high dimensional precision. The particle size of the powder affects not only the precision but also the density of the SLS part. The appropriate particle size is about 75-100 mm.

Polycarbonate (PC) powder, a common and low-cost amorphous polymer, can be moulded easily by the process of selective laser sintering (SLS). However, the sintered parts cannot be used as functional parts because of their poor mechanical properties. In this article, epoxy resin was applied to improve the mechanical properties of PC SLS parts. Specimens for testing dimensional accuracy, tensibility, flexibility, and impact strength were made by SLS with 75-100 mm PC powder. Some of the specimens were posttreated with two types of epoxy resins. Dimensional accuracy and mechanical properties of the specimens were measured. Microstructures of tensile fracture were observed by scanning electron microscopy. The result shows that the mechanical properties of the specimens are reinforced greatly after the epoxy resin has been infiltrated. Extent of the reinforcement depends on curing agents of epoxy resins. For example, with curing agent W, it is increased to 13.82, 8.00, and 3.69 times, respectively, in tensile, flexural, and impact strength and with curing agent Y, it is increased to 19.87, 7.43, and 1.55 times, respectively, in the same properties. The reinforcement in mechanical properties of PC SLS parts can be improved a step further by means of optimizing the epoxy resin system. Therefore, the PC SLS parts reinforced by epoxy resin can be used as functional parts, if the requirement on mechanical properties is not very high.

We designed and developed a new instrument for calibrating micro-force sensors. The calibration is traceable to the SI unit of mass and is realized from 1 µN–60 mN by means of electromagnetic force compensation of a balance. The expanded measurement uncertainty of our instrument comprises two contributions, an absolute contribution of 0.13 µN and a relative contribution of 2700 ppm. We verified our instrument in a bilateral comparison between METAS and PTB's instruments for forces from 40 µN up to 20 mN. The degrees of equivalence found by the two institutes are in excellent agreement.

Finite element analysis (FEA) has become a popular tool for understanding the physical mechanism behind nanoindentation testing and further extracting the mechanical properties of materials under nanoindentation test. However, due to the absence of a reliable method, the accuracy of the FEA model cannot be easily testified, especially since most materials under test are not purely elastic-plastic. Recently, the deformed topography of the interlayer surface has been proposed to be the reference for the evaluation of FEA and other mathematical models for indentation testing. Here an in situ interlayer deformation imaging system based on differential confocal microscopy with neural-network-based signal subdivision is therefore developed, which has the capability to measure in situ the real-time topography deformation within a layered specimen during nanoindentation testing. Preliminary experimental results indicate that the dynamic nanodeformation behaviour (e.g., pile-up, elastic recovery, etc) of the layered materials can be clearly revealed.

No abstract