Fracture and Fatigue Crack Propagation in Injection-Molded Short Fiber-Reinforced Thermoplastics József Karger-Kocsis 2017

Outline Toughness assessment Microstructure due to injection-molding Fracture behavior Fatigue crack propagation (FCP) Outlook

Toughness Determination Methods Standards Fracture mechanics (partly also “standardized”)

Standardized Toughness Testing Methods: Differences Different stress states in specimens Different loading rates (frequency effect) Unnotched and notched samples “Notchology”

Why Fracture Mechanics? - Yields an inherent material parameter - Allows the direct comparison of toughness Standardized toughness determination methods: Charpy (with and without notching; with various notch shapes (v-, u-,double v-); with various notching (direct injection molding, cutting…) Izod (with and without notching) Dynstat Gardner Falling dart etc. the related toughness data can only be compared when exactly the same method and testing conditions were used

Why Fracture Mechanics? Driving force: Determine an inherent material parameter, i.e. independent on specimen size and configuration Linear elastic (stress-related): - Kc, Gc (ASTM E 399-90, ISO 13586; 17281; 15850) Non-linear elastic (energy-related): J-integral (ASTM E 813-81, -87) JR-Curves (ASTM E 1152-87) C(T)OD (ASTM E 1290, BS 5762) Essential work of fracture (EWF)

Is it Possible to Determine the Toughness of Polymers by Fracture Mechanics?

Possibile Toughness Definitions

Factors Infuencing the Mechanical Response of Polymers and Polymeric Composites

then it should depend on structural Molecular and Microstructural Dependence of Fracture Mechanical Parameters If there is an inherent toughness parameter for polymers, then it should depend on structural (i.e. molecular, morphological, microstructural) terms! How to determine possible correlations? Select the right fracture mechanical test method Use well characterized polymers Separate effects controlled by the initial structure from those affected by the loading (loading-induced structural changes)

Fiber Structuring in an Injection-Molded LGF-PP (LGF content: 40 wt.%)

Structure Development due to Injection Molding

Microstructural Parameters of Injection-Molded Discontinuous Fiber-Reinforced Composites

Cutting of CT-Specimens to Study their LEFM Response

Fracture Surface of a T-L Type CT-Specimen of Injection-Molded SGF-PP ( 40 wt.%)

Individual Fiber- and Matrix-Related Failure Events

Local Failure Events E. Belmonte et al.: Composites B, 113 (2017), 331-341

Effects of “Fiber End”

Relation between Fiber Orientation and Effective Fiber Orientation K. Friedrich: Compos. Sci. Techn., 22 (1985), 43-74

Reinforcing Effectiveness of Discontinuous Fiber-Reinforced Injection-Molded Composites J. Karger-Kocsis and K. Friedrich: Compos. Sci Techn., 32 (1988), 293-325

Relative Fracture Toughness vs. R for S(L)GF-PP Composites M= a + n.R

Relative Fracture Toughness vs. Reinforcing Effectiveness (R) Effect of matrix toughness J. Karger-Kocsis et al.: Polym. Bull., 27 (1991), 109-116

Fatigue or Fatigue Crack Propagation? Is any inherent „notch/crack” in injection-molded composites?

Static and Cyclic Fatigue as Assessed by Fracture Mechanics J. Karger-Kocsis in „Wiley Enyclopedia of Composites” (Ed.: L. Nicolais), 2012, pp. 2939-2952

Fatigue Testing S-N; Wöhler diagram V. Altstädt: Adv. Polym. Sci., 188 (2005), 105-152

Fatigue Crack Propagation (FCP) Frequency change during test V. Altstädt: Adv. Polym. Sci., 188 (2005), 105-152

Failure Map: Injection-molded GF/CF-PPS Target: Material development Instead of many quasistatic tests, only one FCP J. Karger-Kocsis and K. Friedrich: J. Mater. Sci., 22 (1987), 947-961

Typical Fatigue Crack Propagation (FCP) Behavior

Effects of MW and Orientation of the Skin-Core Structure on the FCP of Injection-Molded PP

Specimen Preparation for FCP PPS+30 wt% CF K. Tanaka et al.: Eng. Fract. Mech., 123 (2014), 44-58

Crack Growth During FCP PPS+30 wt% CF K. Tanaka et al.: Eng. Fract. Mech., 123 (2014), 44-58

Effects of Volume and Length of GF on FCP of GF-PP-Composites

FCP as a Function of Content and Aspect Ratio of Reinforcement

FCP Rate as a Funcion of the Microstructural Efficiency (M)

Difference between Static and Cyclic Fatigue as Assessed by Fracture Mechanics Test option

Stable Delayed FCP in Discontinuous GF-PP Composites: Cyclic Fatigue

Stable Delayed FCP in Discontinuous GF-PP Composites: Static Fatigue J. Karger-Kocsis et al.: Sci. Eng. Compos. Mater., 2 (1991), 49-67

Creep Superimposed to FCP-Behavior

Future R&D Activities on Injection-Molded Thermoplastic Composites Fracture Microstructure assessment, description and modeling: μCT (computer tomography) mold filling models - Nanocomposites: microstructure – toughness relationship in situ use of additional techniques: acoustic emission, infrared thermography, digital image correlation… … Fatigue crack propagation (FCP) Crack initiation threshold: effects of aging and environments Nanocomposites: Estimation of fatigue life time: using FCP results

Thank you for your attention! E-Mail: karger@pt.bme.hu J. Karger-Kocsis E-Mail: karger@pt.bme.hu