Estimating the Approximation Uncertainty for Digital Materials Subjected to Stress Relaxation Tests

Abstract

The main aim of the study was to determine the goodness of fit between the relaxation function described with a rheological model and the real (experimental) relaxation curves obtained for digital materials fabricated with a Connex 350 printer using the PolyJet additive manufacturing technology. The study involved estimating the uncertainty of approximation of the parameters of the theoretical relaxation curve. The knowledge of digital materials is not yet sufficient; their properties are not so well-known as those of metallic alloys or plastics used as structural materials. Intensive research is thus required to find out more about their behavior in various conditions. From the calculation results, i.e. the uncertainty of approximation of the relaxation function parameters, it is evident that the experimental curves coincide with the curves obtained by means of the solid model when the approximation uncertainty is taken into account. This suggests that the assumed solid model is well-suited to describe a real material.

Design of an Inkjet-Printed Rotary Bellows Actuator and Simulation of its Time-Dependent Deformation Behavior

“…Nevertheless, 3D inkjet printing is considered an important bridging technology and has taken on a significant role in soft robotics and multi-material prototyping as it allows researchers for the manufacturing of conceptual multi-material components with unmatched complexity. Our results confirm the findings of previous reports of the time-dependent mechanical behavior of inkjetprinted elastomers (Kundera and Bochnia, 2014;Adamczak and Bochnia, 2016;Reichl and Inman, 2018) and show similar behavior in complex bellows structures printed from a photocurable elastomer with a Shore A hardness of 30. We analyzed previously published relaxation experiments with linear bellows actuators (Dämmer et al, 2019a), strengthened the experimental basis and found that, on average, reaction forces decreased by 74% within a 89.5 s duration of constant elongation.…”

“…As shown in Figure 7 , the reaction forces dropped from an average of 30.2–7.9 N within the 89.5 s of constant displacement. The marked time dependency of A30 mechanical behavior observed in the experiment supports the findings of previous research ( Kundera and Bochnia, 2014 ; Adamczak and Bochnia, 2016 ; Reichl and Inman, 2018 ; Dykstra et al, 2019 ; Abayazid and Ghajari, 2020 ). A four-term Prony series was then calibrated by curve-fitting Eq.…”

“…Generally, the complex mechanical behavior of PolyJet-printed elastomers in advanced prototypes is challenging: Numerous publications have described non-linear stress-strain relations ( Liljenhjerte et al, 2016 ; Slesarenko and Rudykh, 2018 ; Dämmer et al, 2019a ; Du Pasquier et al, 2019 ; Morris et al, 2019 ) and time-dependent mechanical behavior ( Blanco et al, 2014 ; Kundera and Bochnia, 2014 ; Adamczak and Bochnia, 2016 ; Reichl and Inman, 2018 ). In order to model the constitutive behavior of these materials, researchers have recently calibrated hyperviscoelastic material models by means of uniaxial calibration experiments.…”

Simulation and validation of three dimension functionally graded materials by material jetting

“…Blanco et al measured the stress relaxation modulus of RGD240 (Stratasys) with respect to the printing angle and orientation [35]. While Adamczak and Bochnia conducted physical testing to validate the stress relaxation models for TB+, VW+ and DM50 [36]. In addition, researchers have studied the effects of aging and print orientation on the mechanical properties of TB+, VW+ and some DMs [37], as well as the fatigue behavior of multimaterials samples [38].…”

Material models and finite analysis of additively printed polymer composites

“…As the application area of MJT grows, a need for precise physical properties of the printed materials has been emerged. For example, thermal conductivity, 37 dielectric strength, 38 mechanical strength, 39–41 mechanical relaxation modulus, 42–44 fatigue behavior, 45 and the aging effect on the tensile strength 46 have been investigated to characterize the physical properties of MJT printed materials. While vast research effort has focused on MJT polymers, there is no material characterization and modeling data available for the printed polymer composites or DMs.…”