Characterisation of the cyclic dynamic load behaviour of injection molded integral foam structures

• Applicant: Professor Dr.-Ing. Hans-Peter Heim
• Subject Area: Plastics Engineering ; Mechanical Properties of Metallic Materials and their Microstructural Origins
• Term: from 2018 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 411667746

• Final Report Year: 2023

Final Report Abstract

In this study, the injection molding processing parameters are varied to create the distinctive foam morphologies. Thereafter, a multiple linear and nonlinear regression model is carried out to determine the significant structural features to predict quasi-static and cyclic-dynamic flexural and tensile properties. According to the adopted model, cell distance, homogeneity, sphericity, and cell density are found to be the best explanatory variables to explain the change in flexural strength. The results signify that higher stress is necessary to propagate a crack with a larger cell structure and separation between cells. Cell diameter, sphericity of cells, and homogeneity of cell size distribution are found to be the best variables to predict the response of flexural modulus. The specimen with a smaller cell diameter undergoes a more sudden, brittle, as well as linear fracture. On the other hand, a greater cell diameter accompanied with a higher cell distance results in a better interface bonding and dissipation of the generated heat in the foam structure. The full-field strain histories of each morphology patterns showed that a highly localized strain distribution becomes more inhomogeneous beyond the yield point during quasi-static tensile loading. Stress is concentrated around localized subregions. Differences in the homogeneity of the cell size distribution as well as the distance between cells lead to dissimilarities in the localized high-strain fields. This is because heterogeneity in morphology causes differential elongation of cell walls, where larger cells elongate while smaller cells restrict elongation, leading to higher local deformation and ductile deformation behaviour. Moreover, the common thermoplastic foam morphologies are examined under the cyclic-dynamic tension-tension fatigue test to understand the influence of the overall morphology appearances and resulting corresponding fatigue life, accumulated dissipated energy and dynamic modulus of each morphology pattern. The results show that an increase in average cell distance results in decreasing accumulated dissipated energy. The rate of decrease is initially high and remains relatively constant after a certain increase in cell distance. It was concluded that enhanced cell density with smaller distance between cells improves energy absorption capacity. Furthermore, it was found that the service life of the product with a 50% reduction in density can be extended through a larger cell structure. This phenomenon was also investigated with digital image correlation under cyclic dynamic tensile loading, and it was found that even if crack initiation has already occurred, the sample resists further crack propagation where large cells are encountered in the structure.

Publications

• Findings of Research and Development. Foammelt - Success with low pressure. Virtual, ENGEL Firma, Austria, November 2021
  Güzel, K. & Heim,H.-P.
  
• The Effect of Injection Molding Parameters on Microcellular Foam Morphology. In SPE-Foams
  Güzel, K. & Heim, H.-P.
  
• The Effect of Injection Molding Parameters on Microcellular Foam Morphology. SPE FOAMS. Virtual, 13-16 September 2021
  Güzel, K. & Heim, H.
  
• Determination of In-situ Experimental Mechanical Properties of Injection Molded Thermoplastic Foam Structures. DGM 7th CellMAT. Dresden, Germany, 12-14. November.2022
  Güzel, K.; Zarges, J. & Heim, H.
  
• Effect of Cell Morphology on Flexural Behavior of Injection-Molded Microcellular Polycarbonate. Materials, 15(10), 3634.
  Güzel, Kübra; Zarges, Jan-Christoph & Heim, Hans-Peter
  
• In-situ Visualization of the Influence of Morphological Properties on the Mechanical Deformation Behavior of Physically Foamed Polycarbonate. 37th PPS, Japan, April 2022
  Güzel, K.; Zarges, J. & Heim, H.
  
• Effects of the Cellular Morphology on Fatigue Deformation Mechanisms of Physically Foamed Polycarbonate, SPE Foams, Taipei, Taiwan, 19-20 October 2023
  Güzel, K.; Zarges, J.-C. & Heim, H.-P.
  
• Effects of the Cellular Morphology on Fatigue Deformation Mechanisms of Physically Foamed Polycarbonate. In SPE-Foams, 2023
  Güzel, K.; Zarges, J.-C. & Heim, H.-P.
  
• In-situ full-field deformation analysis of injection-molded microcellular polycarbonate according to foam morphology patterns. Polymer Testing, 124, 108102.
  Güzel, Kübra; Zarges, Jan-Christoph & Heim, Hans-Peter
  
• Potentiale des maschinellen Lernens in der Kunststoffverarbeitung, Wissenschaftlicher Arbeitskreis Kunststofftechnik (WAK), 2023
  Volke, J.; Klute, M.; Güzel, K. & Reit, M.