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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Themes: Fracture in Polymer-based Materials: Structure-Property Relationships
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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ROLE OF INTERFACE ON FRACTURE BEHAVIOR OF POLYMER NANOCOMPOSITES [Keynote]
The interfacial region between nanoparticles and polymer matrix can play a significant role in influencing mechanical behavior of polymer nanocomposites. In this research, the fracture behaviors of three sets of model nanocomposite systems with variation in interfacial properties were prepared and investigated. It is found that rigid nanoparticles can serve both as a reinforcing agent and a toughening agent for polymers if the nanoparticle surface is functionalized appropriately.
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FRACTURE OF UN-NOTCHED BIAXIALLY COLD ROLLED HIGH DENSITY POLYETHYLENE IN TENSION
The fracture surfaces of un-notched tensile specimens prepared from HDPE biaxially rolled at room
temperature and drawn to failure in tension were analyzed using scanning electron microscopy (SEM). The
HDPE sheets were reduced to a thickness of about 80% the initial during the rolling process and the tensile
test was conducted at -40 degrees Celsius and at a strain rate of 100%/min. In comparison to a melt processed sheet of
the same material and thickness, the rolled material exhibited greater work hardening capacity,
homogeneous yield behavior, and improved elongation to failure. The fracture surface manifested in a plane
roughly 45 degrees to the draw direction, and revealed three distinct zones: 1) the damage zone, 2) a fracture
surface associated with slow crack propagation, and 3) a fracture surface associated with rapid crack
propagation. The cross-sectional dimensions of sub-microlayers observed from the fracture surface
suggested that they could have resulted from the affine deformation of spherulitic crystals during the rolling
process.
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POLYMERIC MATERIALS TOUGHNESS MEASUREMENT BY STATISTICAL FRACTOGRAPHY
Parts made of polymers play an ever increasing role in many different industries (i.e. aerospace, medical, automobile, etc…), which are attracted by their very interesting material properties. Therefore, there is a need to understand why and how these parts fail to prevent incidents, reduce cost, and move toward a more sustainable approach to the dimensioning of structures made of this type of material. Here, we seek to apply the statistical fractography method to polymers to achieve this goal. This quantitative approach of the field is based on a deep understanding of the non-linear damage mechanisms at play at the crack tip during propagation, and that is expressed through a model used to bridge the measured fracture surface’s roughness and the fracture properties of the material, such as its toughness Kc. We show that our fractographic approach provides reasonable estimate of the fracture toughness, paving the way for the application of statistical fractography to the failure analysis of polymeric parts.
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FRACTURE AND FATIGUE OF SELECTIVE LASER SINTERED POLYMERIC LATTICE STRUCTURES
Designed cellular lattice structures can be used in many engineering applications. While typically the viscoelastic deformation behavior (stiffness and damping) is utilized in many of these applications, the strength and the fatigue behavior plays an important role for components which are exposed to long-term cyclic loading. Selective laser sintered (SLS) polyamide 12 (PA12) and thermoplastic polyurethane (TPU) materials were investigated in two various lattice structures. A bistable structure based on curved bending beams (BB) and another structure with the combination of bending and torque of the trusses (USF) was designed and produced. To cope with the complexity of the SLS generated structure, three specimen configurations with different printing directions (0° and 90°) were used. To study the bulk behavior cylindrical hollow and notched round-bar specimens, to study the cellular behavior specimens consist of single trusses and knots and specimens contain multiple lattice cells were investigated under both uniaxial and axial/torsional, monotonic and cyclic loading conditions. The monotonic tests provided not only the strength values but relevant material models for subsequent simulations. The cyclic tests were performed at low strains for a comprehensive viscoelastic characterization and at higher strains for fatigue characterization in terms of conventional and strain based S-N curves.
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