Session W2: Wednesday, June 14, 14:00-16:00
Wednesday Jun 14 2023
14:00 - 14:20
INTERFACE CRACK OR DELAMINATION: WHEN & WHERE TO INITIATE? HOW TO PROPAGATE & HOW BIG AREA TO ATTAIN?
After inserting a matrix, secondary layer in between the two adjacent primary layers of the bimaterial, the overall load causing the weakest secondary layer element to fail can be even bigger than the bimaterial’s strength. The stresses in the element must be untrue. In this paper, two modifying coefficients (MCs) are applied to modify the stresses, which are then substituted into a strength failure equation of the matrix. If it is fulfilled, the failed secondary layer element is deleted, and an interface crack occurs within the two adjacent primary layer elements. Continued in this way step by step, all of the interface failure information is available without iteration. Only the critical displacements at the peak loads of a DCB (double cantilever beam) and an ENF (end notched fracture) tests are required as inputs in addition to the material properties of the two primary layers and the secondary layer.
14:20 - 14:40
EXPERIMENTAL AND NUMERICAL STUDY ON THE DELAMINATION BEHAVIOUR OF INTERLEAVED COMPOSITES WITH AUTOMATED TAPE LAYING
Automation of composite materials manufacturing is an important pre-requisite to upscaling the manufacturing without diminishing quality of the end-products. In this research, interleaved composites have been manufactured by modified skip tow automated tape laying (ATL) process, where each tape can cross many tapes multiple times. This tape architecture has been shown previously to reduce delaminations through the internal/inherent crack arresting features. Here, Single Leg Bending (SLB) experiments were carried out to study the delamination behaviour of the interleaved composites under quasi-static loading. It was found that, following from delamination initiation, the crack plane propagated with a new crack regularly deviating/migrating away from the primary inter-tapes crack plane towards other inter-tapes interfaces due to the gaps, misorientations and interleaves between the tapes. The multiple delaminations fracture toughness was qualified by the compliance calibration (CC) method in which the fracture toughness was theoretically calculated by crack length back-calculated specimen compliance, and was also numerically modelled by accounting for large-scale fibre bridging. Moreover, both optical microscopy and X-ray computed tomography were performed to examine defects in the specimens before testing and damage after testing. It was observed that the generation of multiple cracks was heavily depended on the local lay-up structure. This suggests
14:40 - 15:00
EFFECT OF PROCESS-INDUCED DEFECTS ON MODE I BEHAVIOR OF PMCS: RANDOM DEFECTS VS. CONTROLLED DEFECTS
With advances in composite manufacturing, the need to establish process-microstructure-property relations remains an ongoing challenge. Effective property predictions, including damage tolerance behavior of advanced composites, often requires explicit modeling of defects and investigating the onset and propagation of damage. The high porosity level is a more commonly encountered defect in heterogeneous composite materials. The current work uses the cohesive zone modeling (CZM) approach adapted for explicit defects in the crack path within a finite element (FE) numerical framework. Random and controlled pore distributions have been modeled and numerically compared. Experimental efforts toward creating controlled pores in the crack path are ongoing. The execution of the current approach will enable better material behavior predictions for advanced composite materials.
15:00 - 15:20
SCALE EFFECTS IN THE POST-CRACKING BEHAVIOUR OF CNT-EPOXY COMPOSITES: PREDICTING CRACK JUMPS AND DUCTILE-TO-BRITTLE TRANSITIONS
The scale effects on the global structural response of fibre-reinforced brittle-matrix specimens subjected to bending are discussed in the framework of Fracture Mechanics by means of the Updated Bridged Crack Model (UBCM). This analytical model assumes the composite as a bi-phase material, in which both the brittle matrix and the reinforcing fibres contribute to the global toughness. In particular, the bridging mechanism of the reinforcing layers can be described by an appropriate cohesive softening constitutive law, which takes into account the progressive slippage of the fibre inside the matrix. In addition, the discontinuous phenomena, i.e., crack jumps (snap-back) and snap-through instabilities, which experimentally characterize the post-cracking behaviour of the composite, can be captured in a quantitative way. Furthermore, UBCM predicts different post-cracking regimes depending on two dimensionless numbers: the reinforcement brittleness number, NP, and the pull-out brittleness number, Nw. Finally, UBCM simulations of non-smooth crack evolutions are compared to experimental results reported in the scientific literature, in which carbon nanotube-epoxy specimens are tested in bending.
15:20 - 15:40
THERMAL BEHAVIOR DURING FRACTURE OF HYBRID EPOXY/CNT/GNP COMPOSITES
Julkarnyne M Habibur RahmanChestnut
This work reports the distinct thermal signatures during failure of epoxy-based nanocomposites comprised of multi-walled carbon nanotubes (MW-CNTs) and graphene nanoplatelets (GNPs). These fillers individually alter the material properties, but their synergy dramatically improves mechanical performance and other multifunctionality. CNT/epoxy, GNP/epoxy nanocomposites are fabricated and compared with the mixed GNP/CNT/epoxy hybrid nanocomposites containing the same weight percentage. Temperature profiles during tension tests have been observed using an infrared thermography (IR) camera yielding distinctive temperature profiles.
15:40 - 16:00
DETECTION OF MODE I INTERLAMINAR CRACK IN CNF DOPED GFRP LAMINATES USING ELECTRICAL IMPEDANCE TOMOGRAPHY
Electrical impedance tomography (EIT) is an emerging structural health monitoring tool for self-sensing composites using the piezoresistive effect. This work presented a novel methodology to detect interlaminar crack or delamination developed during mode I loading in carbon nanofillers doped glass fiber reinforced polymer (GFRP) composites using EIT. DCB specimens were fabricated with 1 wt% carbon nanofillers (CNF) doped GFRP laminates to produce interlaminar crack under mode I loading. The boundary voltage datasets, obtained from electrodes mounted on top and bottom surface of the specimen, were used to solve the EIT inverse problem to get the reconstructed conductivity change map. This methodology demonstrated that interlaminar cracks can be successfully detected using EIT.
Session W3: Wednesday, June 14, 16:30-18:00
Wednesday Jun 14 2023
16:30 - 16:50
NOVEL SERR-CONTROLLED ENVIRONMENTAL FATIGUE TEST METHODOLOGY FOR ADHESIVE-BONDED LAMINATES
In this paper a novel environmental fatigue test methodology is presented, in which the strain energy release rate (SERR) was controlled during the cyclic experiment at an elevated temperature in humid air. Therefore, an electrodynamic testing machine equipped with a custom-built environmental chamber along with a compatible calculation and controlling software package was used. To determine the crack length based on force and displacement data a compliance-based calibration method was implemented. SERR values were deduced for individual load cycles employing an user defined control channel. The control channel allows for definition of a specific starting point (e.g., 10 J/m²) and an increase rate (e.g., +5 J/m² after 50,000 cycles). By holding the SERR constant over many cycles confidence bands were deduced for the measured crack propagation rates accounting for measurement uncertainties. To corroborate the novel methodology, experiments were conducted on double cantilever beam laminates bonded with soft adhesives in both, a SERR and a displacement controlled mode.
16:50 - 17:10
HEALING OF LAMINATED COMPOSITES AFTER STATIC AND FATIGUE DELAMINATION
In this study, static fracture experiments under mode-I and mixed mode loading, and fatigue testing under mode-I loading were carried out on double cantilever beam (DCB) specimens, and subsequent healing of the delamination was investigated. Thermoplastic healants dispersed in a thermoset CFRP composite were used to perform the healing, triggered through brief heating in an oven. It was observed from the test results that delaminations can be healed efficiently and the healing was found to be repeatable. As a result of healing, significant crack closure was observed and fatigue crack growth rate was considerably reduced. These findings can be helpful in extending the service life of laminated composites.
17:10 - 17:30
INFLUENCE OF THE RANDOMNESS OF FIBER DISTRIBUTION ON THE DISPERSION OF FATIGUE RESPONSE IN STEEL FIBER REINFORCED CONCRETE USING MICRO-COMPUTED TOMOGRAPHY
In this work, the dispersion in the flexural fatigue behavior of steel fiber reinforced concrete is studied. For this purpose, the random distribution of the fibers inside the specimens is analyzed by means of micro-computed tomography. The results reveal that fibers are better positioned in some specimens than in others, which partially explains the scatter of the results. In particular, fiber density or average height around the crack plane show a strong correlation with fatigue life.
Session Th2: Thursday, June 15, 14:00-16:00
Thursday Jun 15 2023
14:00 - 14:20
FATIGUE CHARACTERIZATION OF ADHESIVELY-BONDED GFRP JOINTS VIA SELF-HEATING
High cycle fatigue (HCF) of composite structures is known to exhibit self-heating coupled with stiffness degradation due to progressive damage accumulation. Recent advances have been made in correlating fatigue damage accumulation to full-field temperature fields during the HCF of composite structures. This work uses a thermal medium wave infrared camera to quantify self-heating in adhesively bonded unidirectional glass fiber reinforced polymer (UD-GFRPs) specimens under tension-tension fatigue loading.
14:20 - 14:40
FAILURE MECHANISMS OF STEEL FIBERS EMBEDDED IN HSFRSCC
Luiz Carlos De AlmeidaChestnut
The bond stress transfer between fibers and matrix is the basic resistant mechanism of fiber-reinforced composite materials. Interfacial bond properties and failure mechanisms of the composite are commonly evaluated through single pullout tests on unreinforced matrices. The small size of the molds used to cast the samples prevents the fibers from being randomly distributed in the matrix and makes it difficult to compact the mixture. Krahl et al. (2020) developed an innovative portable pullout machine that allows testing fibers embedded in fiber-reinforced matrices with larger sample sizes. This paper discusses the experimental results of single fiber pullout tests carried out with the portable machine on high-strength fiber-reinforced self-compacting concrete (HSFRSCC). The bond behavior of hooked-end steel fibers and their relationship with the failure mechanisms are analyzed for fiber contents of 0% and 0.75%. The results show that bond and failure mechanisms were influenced by the presence of fibers in the matrix.
14:40 - 15:00
AN ANALYTICAL APPROACH FOR THE FRACTURE CHARACTERIZATION IN CONCRETE UNDER CYCLIC LOADING CONDITION
Many civil engineering infrastructures frequently encounter repetitive loading during their service life. Due to the inherent complexity observed in concrete, like quasi-brittle materials, understanding the fatigue behavior in concrete still poses a challenge. Moreover, the fracture process zone characteristics ahead of the crack tip have been observed to be different in fatigue loading than in monotonic cases. Therefore, it is crucial to comprehend the energy dissipation associated with the fracture process zone (FPZ) due to repetitive loading. It is well known that stiffness degradation due to cyclic loading provides a better understanding of the fracture behavior of concrete. Under repetitive load cycles, concrete members exhibit a two-stage stiffness degradation process. Experimentally it has been observed that the stiffness decreases initially with an increase in crack length and subsequently increases. In this work, an attempt has been made to propose an analytical expression to predict energy dissipation and, later, the stiffness degradation as a function of crack length.
15:00 - 15:20
FRACTURE AND FATIGUE STUDIES ON META-SANDWICH AUXETIC CORE
Inspired by the Parker solar probe's heat shield, a carbon-carbon semi-auxetic laminate sandwiching a lightweight carbon auxetic core has been designed in this work. The fracture and fatigue crack propagation in 2D and 3D auxetic core at ambient and extreme temperatures have been predicted and compared with conventional honeycomb cores and foams. Comparative studies have been performed between the results obtained by in-house codes of phase-field fracture (PFF) in FEniCS and the extended finite element method (XFEM) in ABAQUS™.
Session Th3: Thursday, June 15, 16:30-18:00
Thursday Jun 15 2023
16:30 - 16:50
ON THE DESIGN OF CRACK-ARRESTING LAYERS IN POLYPROPYLENE BASED MULTILAYER COMPOSITES
In natural materials, outstanding properties can be attained through an advantageous combination of different materials in intricate microstructures. Usually, a matrix material contributes high strength and stiffness (“hard phase”), while interlayer (IL) materials are often proteins with low strength and modulus (“soft phase”) but high strains at break. The combination of both phases leads to crack arresting properties, thus dramatically increasing the fracture toughness and damage tolerance of the composite. Renowned examples of such effects are nacre as well as deep-sea sponges. The same concepts shall be mimicked to increase the fracture toughness of talcum reinforced polypropylene (PP). The challenge lies in preserving specimen stiffness while also utililzing the crack arresting properties of soft ILs. In this contribution, two types of PP with different mechanical properties are used as ILs. Normalized parameters for fracture toughness and specimen stiffness are used in order to assess the overall properties of multilayer composites. The trade-offs between stiffness and toughness are illustrated, while optimized structures also demonstrate that both properties can be attained simultaneously.
16:50 - 17:10
TAGUCHI BASED – FUZZY METHOD OPTIMIZATION OF PROPOSED ULTRA-HIGH STRENGTH STEEL /UHMWPE HELMET UNDER VARIABLE IMPACTOR CONDITIONS.
Ultra high strength steel (UHSS) is known for its high strength, high modulus and high energy absorption ability through plastic deformation. However, it is less appealing for lightweight applications due to it relatively high density despite their cheap price. Therefore, all advanced helmets are made from advanced lightweight polymeric materials which are very expensive. The advantages of these classes of material can be harnessed by combining the synergies between them. This study seeks to investigate the application of thin layers of high strength steel and ultra-high molecular weight polyethylene (UHMWPE) in designing cheap and low weight helmet under impact application. Optimization of the proposed helmet under variable impact conditions has been performed through a Taguchi-based fuzzy logic approach. The optimization study investigated the integrity of the proposed helmet considering variable helmet weights, impact velocities and impactor masses. Optimum combinations of these design parameters were obtained through the utilization of Taguchi orthogonal array matrix. Maximization of fracture energy and reaction forces between inner shell and cushion of helmet were considered as criteria for the optimization procedure. Input data for the optimization process were obtained through numerical simulation using the explicit finite element program - LS-PrePost.
17:10 - 17:40
PROGRESSIVE DAMAGE IN CMC MINICOMPOSITES WITH THICK INTERPHASES UNDER TENSILE LOADING [Keynote]
In this work, a composite cylinder assemblage (CCA) model has been used to model the progressive damage behavior under tensile loading of a three-phase ceramic matrix single-tow mini-composite composed of carbon fiber, silicon carbide (SiC) matrix and boron nitride (BN) interphase. A 3-phase shear lag model has been used to capture the matrix crack-driven stress redistribution in the presence of a finite thickness interphase. A probabilistic progressive modeling approach has been proposed to predict the tensile response of ceramic matrix composite (CMC) minicomposites. Multiple matrix cracking, interfacial debonding, and fiber failure have been considered as the damage modes. The predicted tensile response of CMCs from the progressive damage modeling approach agrees with experimental results obtained with C/BN/SiC minicomposites. Finally, the influence of volume fractions, constituent properties, and interfacial properties on the mechanical behavior of CMC minicomposites has been presented.
17:40 - 18:00
NON-DESTRUCTIVE EVALUATION OF DEFECTS IN COMPOSITE BI-MATERIAL STRUCTURES AND ESTIMATION OF FRACTURE FRONT USING DATA DRIVEN TERAHERTZ TIME DOMAIN ANALYSIS
The high luminosity Large Hadron Collider (HL-LHC) will collide particles at unprecedented rates to search for new physics and make high precision measurements to challenge the standard model with emerging technologies that pose high demands for the materials of charged particle tracking detector support structures. Tracking detectors at current (and future) colliders are encounter high-radiation environment where polymeric and carbon fiber composite materials are used in the mechanical support structures of the detectors. The accumulated radiation dose for these materials and thermal loads lead to defects like voids and cracks due to de-gassing and thermal cycling. Terahertz time domain spectroscopy is used to map these strains in a bi-material strip and trace the locations of fractures in a thermal interface material (TIM) layer or an adhesive layer. Statistical data driven terahertz scan image processing analysis is used for predicting the fracture propogation behavior to validate the cohesive FEA model for the fracture observed.
Session F1: Friday, June 16, 10:30-12:30
Friday Jun 16 2023
10:30 - 10:50
SIZE EFFECTS OF COMPOSITE CEMENT AND FUNCTIONALIZED PLASTIC BEAMS: TOWARDS INCREASED DUCTILITY AND ENERGY ABSORPTION
Silpa Soman PazhankaveChestnut
Polyethylene Terephthalate (PET) plastic particles, having been functionalized using a simple, cost-effective, and scalable treatment technique, presented in patented application 17484834, were used as a cement replacement ingredient in plain cement beams. The functionalization increases the affinity of PET to water, and thus their hydrophilicity, enabling the particles to form bonds with Ordinary Portland Cement (OPC) hydration products. The particles were randomly distributed into cement powder during the mixing process. Size effect beams of 4 different geometrically similar sizes were cast in three different percentages (families) of cement replacement with functionalized PET in notched beams to be tested in three-point bending. Bažant’s Type 2 Size Effect Law was used to elucidate the size effects and initial fracture energies (Gf) of all families. The Hillerborg Work-of-fracture method was used to find the total fracture energy (GF). Preliminary results indicate that beams with adequately bonded PET demonstrated improved ductility, caused by crack bridging, as well as increased i) fracture process zone (FPZ) size, ii) Gf and iii) GF, compared to reference OPC beams, while closely preserving the bending strength for larger sizes.
10:50 - 11:10
DEBOND FRACTURE AND KINKING IN MULTILAYER SYSTEMS: THEORETICAL SOLUTIONS AND PRACTICAL APPLICATIONS
Debond fracture is a dominant failure mechanism in multilayer systems used for various current applications, from laminated and sandwich structural components to protective coatings and thermal barrier coatings; from microelectronic devices, in the electronics and flexible electronics fields, to biomedical devices. Debond cracks originate and propagate at the interfaces between the layers, which often have disparate mechanical and thermal properties; they may kink out of the interfaces and lead to unexpected collapses, such as those observed in marine sandwich composites where these mechanisms may yield to the detachment of entire portions of the core from the outer facesheets. The presentation reviews elasticity techniques and closed form solutions recently derived by the authors for the fracture parameters of interface cracks in edge cracked orthotropic layers, bimaterial layers and sandwich beams and for the crack tip compliance coefficients (root rotations and displacements) in bimaterial isotropic and orthotropic layers. Practical applications of the solutions will be discussed: operative formulae for the characterization of the interfacial toughness in classical and novel fracture mechanics specimens; calibration of the parameters of one-dimensional model; and analytical criteria for kinking in multilayer systems.
11:10 - 11:30
EFFECTS OF TEMPERATURE ON FIBER TENSION FRACTURE TOUGHNESS OF COMPOSITE LAMINATES AT HIGH LOADING RATE
The understanding of fracture toughness associated with fibre dominated tensile failure is of great important for safety design of composite structrures threatened by extreme loading conditions, such as high/cold temperature and high rate loading. The dynamic fracture toughness of composite laminates in fibre tension is characterized under different temperatures (e.g. -55 °C, 23 °C and 90 °C) with compact tension (CT) sample, at loading rate of 8 m/s using a tension Hopkinson bar intergrated with a experimental chamber. Digital image correlation (DIC) with high-speed imaging is employed for obtaining the full-field strain fields and crack tip location.