Indentation failure of circular composite sandwich plates

Acknowledgements A. Rajaneesh and A. R. Akisanya acknowledge the financial support from Nanyang Technological University, Singapore through award of Graduate Scholarship and Tan Chin Tuan (TCT) Visiting Fellowship, respectively. I. Sridhar thanks British High Commission, Singapore for facilitating a Collaborative Development Award (CDA) to visit UK Universities for research collaboration.Peer reviewedPostprin

Constructing a complete landslide inventory dataset for the 2018 monsoon disaster in Kerala, India, for land use change analysis

Event-based landslide inventories are important for analyzing the relationship between the intensity of the trigger (e.g., rainfall, earthquake) and the density of the landslides in a particular area as a basis for the estimation of the landslide probability and the conversion of susceptibility maps into hazard maps required for risk assessment. They are also crucial for the establishment of local rainfall thresholds that are the basis of early warning systems and for evaluating which land use and land cover changes are related to landslide occurrence. The completeness and accuracy of event-based landslide inventories are crucial aspects to derive reliable results or the above types of analyses. In this study, we generated a relatively complete landslide inventory for the 2018 monsoon landslide event in the state of Kerala, India, based on two inventories that were generated using different methods: one based on an object-based image analysis (OBIA) and the other on field surveys of damaging landslides. We used a collaborative mapping approach based on the visual interpretation of pre- and post-event high-resolution satellite images (HRSIs) available from Google Earth, adjusted the two inventories, and digitized landslides that were missed in the two inventories. The reconstructed landslide inventory database contains 4728 landslides consisting of 2477 landslides mapped by the OBIA method, 973 landslides mapped by field survey, 422 landslides mapped both by OBIA and field methods, and an additional 856 landslides mapped using the visual image (Google Earth) interpretation. The dataset is available at line uri \u3ehttps://doi.org/10.17026/dans-x6c-y7x2\u3e (van Westen, 2020). Also, the location of the landslides was adjusted, based on the image interpretation, and the initiation points were used to evaluate the land use and land cover changes as a causal factor for the 2018 monsoon landslides. A total of 45 % of the landslides that damaged buildings occurred due to cut-slope failures, while 34 % of those having an impact on roads were due to road cut-slope failures. The resulting landslide inventory is made available for further studies.

Relative performance of metal and polymeric foam sandwich plates under low velocity impact

Relative performance of metal and polymeric foam cored sandwich plates is studied under low velocity impact loading. The metal and polymeric foam sandwich plates are constructed using a core of 40 mm thickness (with two layers of 20 mm each) and aluminum faceplates. Metal foam sandwich plates are constructed using aluminum alloy foam (ALPORAS) core while polymeric foam sandwich plates are constructed using polyvinyl chloride (Divinycell H80 and H250) foam core. Impact experiments are conducted with a hemispherical punch of mass 8.7 kg at a nominal velocity of 5.8 m/s. The effect of stepwise core grading on the maximum dynamic penetration force as well as energy absorption is studied. To maximize the energy absorption or to minimize the mass of the sandwich plate for a given penetration force, alternatives to Alporas foam are chosen based on either equivalent density (H250) or through-thickness compressive yield strength (H80). The increase in penetration force and energy absorption resulting from the choice of H250 in place of Alporas for the same density of the foam as well as the effect of decrease in mass of the sandwich panel by choosing H80 foam in place of Alporas for the same compressive strength of the foam is discussed. Numerical models were developed in LS-Dyna to predict the impact response (force-displacement history) and failure modes. Upperbound analysis is used to estimate the maximum penetration force. Peak force, energy absorption values and failure mode patterns obtained by analytical estimates, experimental measurements and numerical predictions all agree well.Accepted versio

Strength Prediction of Quasi-Isotropic Scaled Laminates in Open Hole Tension Using Damage Rate Bound Mesomodel

peer reviewedThe open hole tension (OHT) test is one of the standard composite material qualification tests at the coupon level. Predicting OHT strengths using finite element models is essential to minimize the number of tests and associated costs. Present article demonstrates the tensile strength prediction of OHT specimens using Ladevèze (LMT-Cachan) mesomodel in conjunction with damage rate bound (DRB) based delay damage. Intra-laminar ply failure and interface failure are taken into account in the current research. These intraply and interface models are coded as user subroutines in LS-Dyna explicit commercial solver. Matrix in-situ strengths are used to account for ply thickness effects in the finite element simulations. Effect of ply, sub-laminate or in-plane scaling effects on OHT strength are investigated. A calibration procedure for the DRB delay damage constants is proposed. The robustness of the DRB delay damage is evaluated in mitigating mesh size effects by considering two types of mesh topologies. All the test data is taken from the scientific literature. Comparison between tests and present finite element predictions is made in terms of failure stress, failure modes and damage sequence events. Predictions from current finite element models matched well in the matrix or delamination failure mode dominated test cases. A reasonably acceptable agreement was observed in test cases with fiber dominant failure

Impact modeling of foam cored sandwich plates with ductile or brittle faceplates

This paper reports numerical results of low velocity impact on open-face sandwich plates with an impactor of 2.65 kg mass hitting with 6.7 m/s velocity. The numerical simulation is done using 3D finite element models in LS-DYNA. The sandwich plates used for the present work have a core made of commercial aluminum alloy foam (Alporas) with faceplates made of either ductile aluminum (Al) or brittle carbon fiber reinforced plastic (CFRP). Selection of suitable constitutive models and erosion criterion for the failure analysis is investigated. A simplified analytical model for the peak load prediction under punch-through failure mode is presented. Numerically predicted contact force versus time, energy absorbed versus time along with the failure modes are compared with the experimental measurements and observations. Within experimental scatter, there is a good agreement between the numerical predictions and experimental measurements. Further more, the analytically predicted peak load values are in excellent agreement with the experimental measurements

Advanced material models for damage and failure analysis of fiber reinforced composite structures

Thin walled composite structures made of laminates with stacks of plies including continuous fibres (like UD or fabrics) are used in aircrafts, wind turbines, naval and automotive applications. In order to propose predictive finite element simulation tools that are necessary to speed-up the time to market of new products, it is important to use material models that can accurately represent different failure modes at the ply level of a laminated composite structure. Additionally, damage at the ply interfaces, that is delamination, must also be taken into account in the model. Modelling progressive damage up to failure in laminated composite material is clearly a very difficult task

Flexural fatigue life prediction of CFRP-Nomex honeycomb sandwich beams

Long-term flexural fatigue life of composite sandwich beams consisting of plain weave carbon 3K-70P/epoxy (CFRP) faceplates and Nomex honeycomb core is studied using time–temperature superposition principle (TTSP) by extending our previous study on laminates [Composites Part B: Engineering (19):539-547, 2016]. Considering negligible effect of temperature on the honeycomb core performance, time-temperature shift factors (TTSF) of the sandwich beams is assumed to be same as that of the CFRP faceplates. Hence, TTSFs are taken from previous laminates study. Constant strain rate (CSR) experiments at various temperatures and strain rates are conducted to construct the CSR master curve, followed by prediction and validation of creep strength master curve. Flexural fatigue tests were then conducted at various temperatures and load levels to construct S-N curves at respective temperatures. Finally, fatigue strength master curve is constructed. Within experimental scatter, predicted fatigue behavior at any given (a) frequency and (b) load ratio is confirmed to be in reasonable agreement with the experimental measurements