Session M1: Monday, June 12, 10:30-12:30
Monday Jun 12 2023
10:30 - 11:10
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.
11:10 - 11:30
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
11:30 - 11:50
POLYMERIC MATERIALS TOUGHNESS MEASUREMENT BY STATISTICAL FRACTOGRAPHY
Guillaume De LucaHazelnut
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.
11:50 - 12:10
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.
12:10 - 12:30
TALK MOVED TO SESSION Tu1
Session M2: Monday, June 12, 14:00-16:00
Monday Jun 12 2023
14:00 - 14:20
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
14:20 - 14:40
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.
14:40 - 15:00
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.
15:00 - 15:20
MEASUREMENT AND FE-MODELING OF THE EFFECTS OF STRESS TRIAXIALITY ON THE NECK INITIATION AND FAILURE OF HIGH-DENSITY POLYETHYLENE
Md Shafiqul IslamHazelnut
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.
15:20 - 15:40
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.
15:40 - 16:00
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.
Session Tu1: Tuesday, June 13, 10:30-12:30
Tuesday Jun 13 2023
10:30 - 10:50
THE IMPACT OF CURING TIME AND MOLD TEMPERATURE ON THE FATIGUE BEHAVIOR OF NITRILE BUTADIENE RUBBER
To complement the present research results in the field of fatigue and fracture in elastomers, an analysis of the influence of curing time and mold temperature on the fatigue properties of a carbon black-filled industrial NBR compound was carried out. There was a significant difference in the crack growth rate with respect to the different manufacturing conditions.
10:50 - 11:10
ENVIRONMENTAL STRESS CRACKING RESISTANCE (ESCR) OF RECYCLED PP (RPP) FROM AND FOR YOGURT CUPS
Recycling of plastic packaging waste is a promising approach towards a circular economy due to the high amount used and the short application time. This paper uses the concept of environmental stress cracking resistance (ESCR) to investigate the fatigue behavior of recycled yogurt cup materials. As test environments air and oil where chosen, where the latter imitates the fatty structure of yogurt. Therefore, four fractions of manually sorted post-consumer polypropylene yogurt cup waste was shredded to flakes and washed with different temperatures and media. Additionally, one of these fractions was blended with varying amounts of virgin pipe material. Furthermore, the reference material, which is currently used for yogurt cups was tested for comparison. Various influences of the fatigue tests were detected, which are a more pronounced influence of oil than of air, especially for recyclates but also for virgin materials and a significant improvement of the recyclates which were blended with a pipe grade material.
11:10 - 11:30
STRUCTURAL STUDY OF AP-HTPB COMPOSITE UNDER IMPACT LOADING
The impact response of a composite material is dependent on its microstructure. This study examines the effect of particle size and impact velocity on the temperature rise and strain rate in a composite material containing Ammonium Perchlorate (AP) crystals and Hydroxyl-terminated polybutadiene (HTPB) binder by combining computational and experimental work. Samples of AP-HTPB composite, with AP crystal sizes of 200 and 400 μm, respectively, are impacted at velocities ranging between 5-10 m/s. A volume fraction of 70-80% AP is maintained in each sample.
11:30 - 11:50
INVESTIGATION OF THE CRACK DEFLECTION/PENETRATION PROBLEM IN EXTRUSION-BASED ADDITIVELY MANUFACTURED POLYMERIC MATERIALS
Components produced via polymeric additive manufacturing (AM), especially extrusion based methods, possess many weld lines between strands and layers. Thus, the failure of these structures is often dominated either by crack deflection between or crack penetration through individual strands. Two methods to predict the failure mode are those of Cook and Gordan, and of He and Hutchinson. In this work, the applicability of both approaches has been tested on four different polymeric materials. It was observed that the two criteria are quite limited in predicting the correct failure mode. Not only printing temperature also the formation of contact area, the diffusion between the individual strands as well as the resulting morphology of the material were found to play a key role for predicting the crack deflection/penetration problem.
11:50 - 12:10
IN-SITU EXPERIMENTAL INVESTIGATION OF FATIGUE CRACK PROPAGATION MECHANISMS IN POLYMER ELECTROLYTE MEMBRANE OF FUEL CELL UNDER OVERLOADING EFFECT
The fatigue crack growth mechanisms in polymer electrolyte membranes of fuel cell are investigated under single overload conditions. In-situ SEM testing and in-situ optical microscopy testing combined with digital image correlation technique are conducted. The results show that the residual stress dominates the fatigue crack growth after the application of small overload cycle leading to subsequent fatigue crack growth retardation while larger overload cycle causes crack tip sharpening, resulting in fatigue crack growth retardation reduction or even acceleration.
Session Tu2: Tuesday, June 13, 14:00-16:00
Tuesday Jun 13 2023
14:00 - 14:40
INFLUENCE OF TEMPERATURE AND TESTING MEDIA ON FATIGUE CRACK GROWTH PERFORMANCE OF POLYETHYLENE TESTED VIA CRACKED ROUND BAR SPECIMEN [Keynote]
Paul J. FreudenthalerHazelnut
Static loading test methods to characterize the resistance against slow crack growth use surfactants to shorten testing times. In comparison, the cracked round bar test method uses cyclic loading but no accelerating media and/or temperatures. To allow for a comprehensive knowledge on the effect of media influence, this research investigates the effect of air as well as deionized water with and without surfactant on the crack growth performance of blow-molding polyethylene in cracked round bar experiments at various temperatures. As also seen in literature, first test results show a crack growth decelerating effect of surfactant in cyclic tests at an elevated temperature. Ongoing tests will show the temperature dependency of these effects.
14:40 - 15:00
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.
15:00 - 15:20
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.
15:20 - 15:40
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.