Development of an energy-based approach for optimized frequency selection for fatigue testing on polymers – Exemplified on polyamide 6

Hülsbusch, Daniel; Kohl, Andreas; Striemann, Patrick; Niedermeier, Michael; Strauch, Joachim; Walther, Frank

doi:10.1016/j.polymertesting.2019.106260

Cited by 15 publications

(12 citation statements)

References 22 publications

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“…A further crucial aspect when considering hybrid laminates for applications under cyclic loading is self-heating, which mainly influences the mechanical properties of the polymer component. This is due to the viscoelastic material behavior of polymers, caused by material damping associated with dissipation of energy [ 15 , 16 ]. The intensity of self-heating is load- as well as frequency-dependent [ 17 , 18 , 19 ], since the dissipated energy increases with both and therefore the temperature of the material.…”

Section: Introductionmentioning

confidence: 99%

Testing Procedure for Fatigue Characterization of Steel-CFRP Hybrid Laminate Considering Material Dependent Self-Heating

et al. 2021

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Combining carbon fiber reinforced polymers (CFRP) with steel offers the potential of utilizing the desired characteristics of both materials, such as specific strength/stiffness and fatigue strength of fiber reinforced polymers (FRP) and impact resistance of metals. Since in such hybrid laminates multiple material layers are combined, a gradual failure is likely that can lead to changes in mechanical properties. A failure of the metal partner leads to an increase in stress on the FRP, which under fatigue load results in increased self-heating of the FRP. Therefore, a suitable testing procedure is required and developed in this study, to enable a reproducible characterization of the mechanical properties under fatigue load. The resulting testing procedure, containing multiple frequency tests as well as load increase and constant amplitude tests, enabled characterization of the fatigue performance while never exceeding a testing induced change in temperature of 4 K. In addition to the development of the testing procedure, an insight into the manufacturing induced residual stresses occurring in such hybrid laminates, which impacts the load-bearing capacity, was established using finite element simulation. The gathered data and knowledge represents a basis for future in-depth investigations in the area of residual stress influence on the performance of hybrid laminates and highlights its importance, since not only the used testing procedure determines the measured fatigue performance.

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Section: Introductionmentioning

confidence: 99%

Testing Procedure for Fatigue Characterization of Steel-CFRP Hybrid Laminate Considering Material Dependent Self-Heating

et al. 2021

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“…One major reason is self-heating, which is why a separate consideration of load dependency and testing frequency (hereinafter referred to as frequency) dependency needs to be taken into account. The reason for self-heating is the thermoelastic effect, caused by material damping associated with viscoelastic dissipation and friction [ 35 , 36 , 37 ]. To identify the self-heating behavior, thermography plays a significant role as it is possible to detect the formation of a frequency and load-dependent temperature plateau after a comparative short testing duration (N >> 10 4 ) at loads markedly below ultimate tensile strength (UTS) [ 34 , 35 , 38 ].…”

Section: Introductionmentioning

confidence: 99%

“…To identify the self-heating behavior, thermography plays a significant role as it is possible to detect the formation of a frequency and load-dependent temperature plateau after a comparative short testing duration (N >> 10 4 ) at loads markedly below ultimate tensile strength (UTS) [ 34 , 35 , 38 ]. Due to a higher energy input, the self-heating increases with advancing load level [ 37 , 39 ]. In addition to specimen geometry [ 34 ], the frequency not only has a sensible influence on the self-heating but also regarding the lifespan of short fiber reinforced plastics.…”

Section: Introductionmentioning

confidence: 99%

“…With this procedure, it is possible to shorten the testing duration by use of a thermal-applied optimized frequency for each load step while minimizing the occurring ratcheting at the necessarily low frequency for high load testing. As a result, a load step and load ratio-dependent limit frequency based on energy input is introduced in such a way that the self-heating remains constantly under ΔT < 2 K [ 37 ]. This enables a comparative characterization method while still reducing the overall testing duration; however, the feasibility of applying such an approach to short fiber reinforced plastics is still unknown.…”

Section: Introductionmentioning

confidence: 99%

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Constant Temperature Approach for the Assessment of Injection Molding Parameter Influence on the Fatigue Behavior of Short Glass Fiber Reinforced Polyamide 6

et al. 2021

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Short glass fiber reinforced plastics (SGFRP) offer superior mechanical properties compared to polymers, while still also enabling almost unlimited geometric variations of components at large-scale production. PA6-GF30 represents one of the most used SGFRP for series components, but the impact of injection molding process parameters on the fatigue properties is still insufficiently investigated. In this study, various injection molding parameter configurations were investigated on PA6-GF30. To take the significant frequency dependency into account, tension–tension fatigue tests were performed using multiple amplitude tests, considering surface temperature-adjusted frequency to limit self-heating. The frequency adjustment leads to shorter testing durations as well as up to 20% higher lifetime under fatigue loading. A higher melt temperature and volume flow rate during injection molding lead to an increase of 16% regarding fatigue life. In situ Xray microtomography analysis revealed that this result was attributed to a stronger fiber alignment with larger fiber lengths in the flow direction. Using digital volume correlation, differences of up to 100% in local strain values at the same stress level for different injection molding process parameters were identified. The results prove that the injection molding parameters have a high influence on the fatigue properties and thus offer a large optimization potential, e.g., with regard to the component design.

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“…The instrumentation of mechanical test setups with physical sensors for characterization of deformation and damage initiation and evolution during a mechanical loading is the state of the art for various materials [11][12][13]. Monitoring of material reactions, like deformation [14], change in temperature [15] or electrical resistance [16], and acoustic emissions [17,18], allows an assessment of the structural integrity and identification of occurring damage mechanisms of the tested specimen before final failure [19]. By combining mechanical testing with analytical techniques, like scanning electron microscopy (SEM) or microfocus computer tomography (µCT), an optical characterization of microstructural changes during loading can be realized and correlated with the macroscopic deformation behavior [20].…”

Section: Introductionmentioning

confidence: 99%

In Situ Characterization of Damage Development in Cottonid Due to Quasi-Static Tensile Loading

2020

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Cottonid is a layered material based 100% on cellulose that holds excellent material properties by being completely sustainable. The finite nature of petroleum-based resources nowadays makes these properties significant for technical applications again. To understand how Cottonid reacts to application-oriented mechanical loads and how it fails, development of microstructural damage on the surface and in the volume of Cottonid was studied using innovative in situ testing techniques for the first time. Quasi-static tensile tests were comparatively performed in a scanning electron microscope as well as a microfocus computer tomograph, and the development of defects present in the initial condition of the material was investigated. In the elastic region, no visible damage initiation on the surface and a decrease of overall void volume within the gauge length could be detected. When reaching the yield strength, crack initiation on the surface starts at critical areas, like pores and microcracks, which propagation and assembly could be visualized via scanning electron micrographs. In the plastic region, an increase in void volume could be shown in the gauge length until final failure of the specimen. Innovative material testing techniques presented in this study support lifetime estimation in technical applications and understanding of process–structure–property relations. Particularly, characterization of microstructural damage development due to a mechanical load, which leads to final failure of the specimen, is essential to be able to create material models for lifetime prediction in respect to variable manufacturing or application parameters.

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Development of an energy-based approach for optimized frequency selection for fatigue testing on polymers – Exemplified on polyamide 6

Cited by 15 publications

References 22 publications

Testing Procedure for Fatigue Characterization of Steel-CFRP Hybrid Laminate Considering Material Dependent Self-Heating

Testing Procedure for Fatigue Characterization of Steel-CFRP Hybrid Laminate Considering Material Dependent Self-Heating

Constant Temperature Approach for the Assessment of Injection Molding Parameter Influence on the Fatigue Behavior of Short Glass Fiber Reinforced Polyamide 6

In Situ Characterization of Damage Development in Cottonid Due to Quasi-Static Tensile Loading

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