Morphological and mechanical properties of foamed thick-walled Wood-Plastic-Composite structures

Microcellular wood fiber reinforced polymers offer the possibility to reduce the use of fossil raw materials. In particular, thick-walled structures with thicknesses greater than 6 mm offer a high potential for weight savings. This study investigates the cell structures and mechanical properties of injection-molded test specimens. The influence of different thicknesses (6–10 mm) along with different chemical blowing agents (endothermic, exothermic) with varying dosages (0–2 wt%) is analyzed. The investigations reveal that exothermic chemical blowing agents form finer cells consistently to thin-walled structures than endothermic ones. Higher foaming agent content leads to higher pore fractions, with many small cells coalescing into a large open-pore cell network. The mechanical properties depend mainly on the pore content of the sample. The specific tensile properties deteriorate with the use of chemical blowing agents (CFA), whereas the sandwich structure produced with compact edge layers has a positive influence on the specific flexural properties.

Scientific Advancements in Composite Materials for Aircraft Applications: A Review

Recent advances in aircraft materials and their manufacturing technologies have enabled progressive growth in innovative materials such as composites. Al-based, Mg-based, Ti-based alloys, ceramic-based, and polymer-based composites have been developed for the aerospace industry with outstanding properties. However, these materials still have some limitations such as insufficient mechanical properties, stress corrosion cracking, fretting wear, and corrosion. Subsequently, extensive studies have been conducted to develop aerospace materials that possess superior mechanical performance and are corrosion-resistant. Such materials can improve the performance as well as the life cycle cost. This review introduces the recent advancements in the development of composites for aircraft applications. Then it focuses on the studies conducted on composite materials developed for aircraft structures, followed by various fabrication techniques and then their applications in the aircraft industry. Finally, it summarizes the efforts made by the researchers so far and the challenges faced by them, followed by the future trends in aircraft materials.

Experimental investigation on the forming and evolution process of cell structure in gas counter pressure assisted chemical foaming injection molded parts

By using a standard stretch spline as the research object, the influence of gas counter pressure (GCP) technology on melt foaming behavior in chemical foaming injection molding (CFIM) process was investigated. Related experimental line for GCP assisted CFIM foam was designed, and the effect of GCP technology on melt flow front, spline surface quality and internal cell was studied. According to the results obtained from the experiment, two critical GCP pressures and one critical GCP holding time were innovation proposed. Two critical GCP pressures are the critical GCP pressure of melt flow front cell not cracking and the critical GCP pressure of melt not foaming, respectively. The critical GCP holding time is the secondary foaming behavior time. Based on the proposed critical GCP pressures and critical GCP holding time, the influence mechanism of GCP technology on melt foaming action during CFIM process was revealed.

Comparative Effects of mEOC on the Structures and Properties of PP/SGF and PP/EOC/SGF Composite Foams

To improve the impact toughness of short glass fiber (SGF) reinforced polypropylene (PP) composite foams, maleic anhydride grafted ethylene-α-octene copolymer (mEOC) was employed as impact modifier and interfacial compatibilizer. And for comparison, mEOC was also introduced into PP/EOC/SGF composite foams. Then, the foaming qualities, interfacial structures and mechanical properties of samples against varying mEOC contents were examined and compared in detail. Results showed that adequate mEOC significantly improved the foamabilities of the composites, while the optimized mass fraction was 8% for PP/SGF composite foams and 3% for PP/EOC/SGF system. Increased mEOC facilitated the higher impact toughness, which was increased by 77% for PP/SGF composite foams, whereas only 5% for PP/EOC/SGF foams. However, the flexural strengths were just improved slightly, while compressive strengths decreased monotonically with mEOC for the investigated composite foams.

Influence of relative low gas counter pressure on melt foaming behavior and surface quality of molded parts in microcellular injection molding process

A complex medical instrument exterior shell was chosen as a studying object to investigate the influence of relative low (<10 MPa) gas counter pressure process on microcellular injection molding process. The gas counter pressure microcellular injection mould and related experiments were designed. The relative low gas counter pressure under which the melt can foam was mainly considered to improve the surface quality of molded parts without significantly prolonging production cycle. The effects of the gas counter pressure parameters on the surface quality, cell morphology, and cell density of microcellular parts were studied. A critical melt flow front pressure to effectively eliminate surface swirl marks of microcellular injection molded part was proposed. The mechanism of the influence of gas counter pressure process on foaming behavior of melt in filling process was analyzed. The reasonable gas counter pressure parameters to improve surface quality of products without significantly increasing molding cycle were obtained. By using the obtained reasonable gas counter pressure parameters, a sound microcellular injection molded product was injected finally.

Mechanical properties and foaming behavior of injection molded cellulose fiber reinforced polypropylene composite foams

This paper investigates the effects of cellulose content and processing conditions on the mechanical properties and foaming behavior of injection molded cellulose fiber reinforced polypropylene composite foams. Composite foams were injection molded using an advanced structural foam molding machine with N2 as a physical blowing agent. Foamed specimens were prepared at different injection speeds and void fractions. The mechanical properties and foam morphologies of the specimens were evaluated. The results suggested that the specific flexural modulus was increased and the specific flexural strength and Izod impact strength were maintained by foaming, and that the strength, modulus, and notched Izod impact strength increased with the increase of cellulose content. Additionally, the results suggested that the cell morphology of the composite foams was improved by the increase of void fraction and the addition of cellulose fiber.