Mechanical properties and fracture characterization of additive manufacturing polyamide 12 after accelerated weathering

Mika Salmi,Jouni Partanen,Tuomas Puttonen

doi:10.1016/j.polymertesting.2021.107376

Abstract

The additive manufacturing (AM) methods, selective laser sintering (SLS) and multi jet fusion (MJF), are increasingly used for end-use polymer parts. Chemical reactions caused by ionizing radiation and catalyzed by oxygen, moisture, and heat are known to degrade the polymer structure, result in visual defects, and loss of mechanical properties. However, the effects of the AM layer-wise manufacturing process on polymer degradation are not widely studied. Yet, they may have implications on the mechanical properties and fracture mechanisms of the components.This paper presents an open access data repository of mechanical properties after weathering for AM plastics, conventionally manufactured plastics, and for two clear protective coatings. All materials were exposed to a 1500-h accelerated weathering cycle (ISO-4982-3) followed by tensile testing (ISO-527). Special attention was given to polyamide 12 (PA12) produced via powder bed fusion AM in two build orientations. The fracture surfaces of PA12 and glass-filled PA12 were further studied with scanning electron microscopy. The AM materials were PA12, glass-filled PA12, and carbon reinforced PA12. Traditionally manufactured materials included glass-filled and molybdenum disulfide-filled PA66, PMMA, ABS, PC, and cast PA12.No clear differences were found between the AM build orientations in fracture mechanisms or weathering performance. AM and cast PA12 were strongly affected by accelerated weathering. Carbon reinforced PA12 with a UV varnish experienced the least changes. Weathering resistance was increased with protective coatings. However, an increase in the deviation of mechanical properties with the coatings was observed. The contrary results in ductility for the glass-filled and molybdenum disulfide-filled PA66 after weathering would merit further studies.

Highlights

Plastics are a material class developed and studied extensively from the early 20th century and have been mass-produced for almost a hundred years [1]
This paper presents a broad dataset and provides a compara tive analysis of accelerated weathering effects on the mechanical prop erties and fracture surfaces of additive manufacturing (AM) polyamide 12 (PA12) and glass-filled PA12, along with a wide selection of traditionally manufactured engineering plastics
The study provides an analysis of mechanical properties and fracture characterization of non-weathered and weathered engineering plastics manufactured both with powder bed fusion AM and conventional methods

Summary

Introduction

Plastics are a material class developed and studied extensively from the early 20th century and have been mass-produced for almost a hundred years [1] Their light weight, adaptable mechanical properties, and easy manufacturability make them suitable for the manufacture of products ranging from disposable packaging to high-end engineering applications. The two most used technologies under PBF, are selective laser sintering (SLS) and multi jet fusion (MJF) In both techniques, thermoplastic material in the form of fine spherical powder is heated, consolidated, and solidified layer-by-layer to form three-dimensional objects. The mechanical properties differ depending on the build orientation and layer thickness [11] These characteristics, in addition to the lower speed of manufacturing and a need for post-processing to achieve an adequate surface finish, are among the points listed by companies when discussing barriers to wider AM implementation [12]. Many common engineering plastics, such as PE, PP, PS, TPE, PA6, PEK, and PEEK are already commercially available and new materials are constantly in development [11]

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