Themes: Fracture in Polymer-based Materials: Structure-Property Relationships

REACTIVE TELECHELIC POLYETHERIMIDE TOUGHENED TETRAFUNCTIONAL EPOXY

Highly crosslinked multifunctional epoxy resins possess superior properties, like high Tg, modulus, chemical resistance, etc, yet they are brittle due to their high crosslink density. It is desired that toughness improvements should not compromise other properties, including mechanical, thermal properties, and processability. Here, reactive polyetherimide containing amine functional end groups with two different molecular weights and loading levels were incorporated in tetraglycidyl diamino diphenyl methane tetrafunctional epoxy resin to study their structure-property relationship.
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FRACTURE CHARACTERIZATION OF DUCTILE POLYMERS: RECENT APPLICATIONS OF THE LOAD SEPARATION CRITERION

For ductile polymers, the development of sound relationships between material structure and fracture response calls for the use of robust testing methodologies able to measure properties that describe the different processes occurring during fracture. The most common testing methods used with these materials appear inadequate, and there is a need to examine new approaches. This paper describes the most recent applications of the load separation criterion (LSC) in the fracture characterization of ductile polymers: the testing procedures are introduced and some representative results shown.
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RUPTURE OF HYDROGELS

Hydrogels are soft, highly deformable materials with applications ranging from soft actuators to natural and synthetic biomaterials. The rupture of hydrogels generally involves very large deformations that can be strongly coupled to the fluid flow. In this paper, a modified J-integral (J*) is used to calculate the critical energy release rate utilizing either a critical stretch criterion or the measured overall force-extension relation for a SENT specimen of a fibrin gel, which is the primary stress-carying component of blood clots.
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THERMAL AND VOID VOLUME FRACTION PROFILES IN 3D FOR A DENT SPECIMEN OF NEAT AND GLASS OF SYNTACTIC POLYPROPYLENE MATERIALS

Glass of syntactic polypropylene (GsPP) is used for thermal insulation of subsea pipelines. This contribution displays the temperature and deformation fields in 3D on Double Edge Notched Tensile (DENT) specimens, made of both polypropylene (PP) matrix and GsPP. The influence of the microstructural and the thermal changes in the notched section on the load versus crack opening displacement curve is analyzed. The definition of the crack initiation in relation to a critical void volume fraction is discussed
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FEM MODELING ON SCRATCH BEHAVIOR OF MICRO-PATTERNED POLYMER SURFACE

Polymers are inherently scratch-sensitive due to their low resistance to deformation. Surface patterning is a viable strategy to achieve better scratch performance. In this paper, we model the scratch behavior of micro-patterned surfaces using FEM simulation by employing the powerful coupled Eulerian-Lagrangian approach. The effect of two different pattern types on the scratch behavior of polycarbonate was studied and validated with available experimental results. Results support the use of patterned surfaces in improving scratch performance.
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FULL PMMA KINETIC LAW OF FRACTURE: FROM QUASI-STATIC TO DYNAMIC REGIME

This study uses digital image correlation for the extraction of the stress intensity factor of PMMA in quasi-
static and dynamic regime. The area quantification induced by the cracking of PMMA is a major focus of
this work. Created surface resulting from crack propagation was measured over the entire length of test
pieces. At approximately 0.6 c R , the amount of fracture surface created is higher than twice the projected
fracture surface on the average fracture plane, close to the “mirror” zone. Kinetic laws representing K ID and
G ID according to the crack speed are thus compared with those from the literature by considering dynamical
effects induced by rapid crack propagation. The dynamic fracture energy must be considered as a function
of created surface since the microcrack branching velocity has been reached.
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MEASUREMENT AND FE-MODELING OF THE EFFECTS OF STRESS TRIAXIALITY ON THE NECK INITIATION AND FAILURE OF HIGH-DENSITY POLYETHYLENE

This study analyses the tensile deformation of neck i.e localization initiation, propagation and failure of injection-moulded polymer composed of high-density polyethylene (HDPE) as a function of initial stress triaxiality. Three different specimen geometries namely i) Simple tension, ii) Plane strain and iii) Shear specimens were punched from injection-moulded HDPE plates and tested experimentally in uniaxial tension to induced different stress triaxialities. Based on the major-minor strain paths from digital image correlation (DIC) measurements stress triaxiality has been calculated. It is challenging to follow the stochastic pattern at larger local strain in DIC and hence the strain at failure has been measured using orthogonal grid lines on the specimen surface. Strains at neck-initiation and failure at three different stress triaxialities for injection-moulded HDPE in two material orientations were implemented in finite lement model. ISIGHT with Abaqus was used for calibration of hardening behaviour, triaxiality dependent neck initiation and failure.
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DISK-SHAPED COMPACT TENSION & COMPACT TENSION TESTS ON QUASI-BRITTLE THICK CELLULAR STRUCTURAL ADHESIVE: EXPERIMENTAL AND NUMERICAL ANALYSES

This paper deals with fracture mechanics analysis to study and understand the effect of density on the crack initiation resistance of a thick cellular structural adhesive. Disk-shaped compact tension and compact tension samples of two different densities have been fractured and analyzed. The crack opening has been stabilized making possible the crack growth resistance curve computation. The behavior of the material has then been shown to be quasi-brittle. A numerical simulation of the tests using finite elements and virtual crack closure technique has been performed to extract the evolution of an equivalent elastic crack length associated to the measurable sample elastic stiffness decrease along the test. The resistance curve has then been estimated by applying the equivalent linear elastic fracture mechanics.
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DUCTILE FAILURE OF A PLASTICIZED POLYVINYLCHLORIDE DURING AIR BAG DEPLOYMENT

The present work addresses the ductile fracture process of a plasticized Polyvinylchloride (PVC), constituting the skin of the dashboard, with the goal of ensuring the security of passengers for the automotive industry. Clamped single edge notch bending (SENB) specimens were used to characterize the mechanisms of crack initiation and propagation for the studied material. The ductile failure of the plasticized PVC, by using fracture mechanics tools, was characterized thanks to the exploitation of the experimental database associated with finite element simulation of the crack propagation.
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