Sandwich panels with carbon fiber reinforced plastics (CFRP) have high flexural strength-to-weight and stiffness-to-weight ratios and are used in structures requiring good mechanical properties, such as aircrafts and marine vehicles. In this study, the overall displacement of a sandwich panel with CFRP faces and an aluminum honeycomb core was reconstructed using the inverse finite element method (iFEM). The full in-plane strain fields were input into the iFEM and reproduced from the measured strains and an interpolation technique. We propose an interpolation method to calculate the overall strain fields on the sandwich panel based on strain distributions measured by fiber-optic sensors and numerically showed that the fully distributed sensing yields accurate and robust results in both strain and displacement reconstructions. To validate the proposed method, fiber-optic sensors were embedded in the sandwich panel, and strain distributions were measured by the sensing system with optical frequency domain reflectometry. In these experiments, we successfully and accurately measured the strain distributions along the embedded fibers and reconstructed the overall strain fields and displacement of the sandwich panel under four load cases. Furthermore, the sandwich panel shape identified by the proposed method can be employed for structural health monitoring.

This article focuses on design of an Artificial Neural Network (ANN) model to estimate ship resistance in ice-covered water by using suitable ship and ice parameters. In order to develop a reliable model, as much ice resistance test data as from the ship sea trials and model test measurements are collected to train the neural network. Different features (ship design parameters and ice mechanic properties) are explored to find a suitable combination of input features. Several algorithms are tested and compared to select a good model for resistance prediction. It turns out that seven features and the Radial Basis Function - Particle Swarm Optimization algorithm (RBF-PSO) can provide a reasonable generalization model. This study shows that the ice resistance predicted by the ANN correlates well with the measured data. The model developed herein can be used as an ice resistance prediction tool with high accuracy compared to the conventional semi-empirical formulae used in polar ship design.

Inland waterway (IWW) shipping is a sustainable opportunity to reduce traffic on, in many times very congested, roads and railways. This is especially true for cities and urban areas. However, for an operator, the ship Operation Time Window (OTW) is important in order to predict possible business cases, especially for regions with long-term winter seasons with icy conditions. The OTW indicates the probable number of navigable days for the ship. The operability is in relation with ship speed, ice thickness, whereas the ship resistance is of significant relevance. This study proposes a model to investigate the possibility of a certain operating condition for ice-going ships based on an Artificial Neural Network (ANN) model and a statistical model. To demonstrate the proposed method for calculating the ship OTW of an IWW, a case study is performed. Ice condition in Lake Mälaren (in Sweden) and an IWW ship designed to maximise its dimension restrictions are used for this case. The Radial Basis Function-Particle swarm optimization (RBF-PSO) ANN model is used to predict ice resistance in level ice conditions. Given the ice resistance prediction, a statistical analysis is further conducted regarding to the ice thickness distribution and the operational ship speed distribution to obtain ship OTW. Comparisons are made between semi-empirical ice resistance prediction methods and the ANN model. The influence of different ship speed distribution profiles is investigated by performing a parametric study. The OTW model can be used to evaluate ship operational scenarios in ice-covered waters for ship designers and owners.

The current study focuses on the impact loading phase characteristic of thin first year ice in inland waterways. We investigate metal grillages, fibre reinforced plastic (FRP) composites and nature-inspired composites using LS Dyna. The impact mode is modelled as (a) simplified impact model with a rigid-body impactor and (b) an experimentally validated ice model represented by cohesive zone elements. The structural concepts are investigated parametrically for strength and stiffness using the simplified model, and an aluminium alloy grillage is analysed with the ice model. The metal–FRP composite was found to be the most favourable concept that offered impact protection as well as being light weight. By weight, FRP composites with a Bouligand ply arrangement were the most favourable but prone to impact damage. Further, aluminium grillage was found to be a significant contender for a range of ice impact velocities. While the ice model is experimentally validated, a drawback of the simplified model is the lack of experimental data. We overcame this by limiting the scope to low velocity impact and investigating only relative structural performance. By doing so, the study identifies significant parameters and parametric trends along with material differences for all structural concepts. The outcomes result in the creation of a viable pool of lightweight variants that fulfil the impact loading phase. Together with outcomes from quasi-static loading phase, it is possible to develop a lightweight ice-going hull concept.

Composite sandwich materials provide high bending performance-to-weight ratios. However, these materials are vulnerable to impact damages which can drastically reduce their load-bearing capability. Presently there is a lack of standardised test methods for impact assessment. This study compares three different test methods for impact assessment; single skin compression after impact (CAI-SS), sandwich compression after impact (CAI-SW) and four-point bending-after-impact (BAI). The CAI-SS test method shows high compressive strength and strain at failure and the tesr is relatively easy to evaluate. For finite size plates with significant impact damage, the CAI-SS test method is recommended for post impact strength assessment. For large sandwich panels with relatively small impact damages the CAI-SW test method could be more relevant since it includes effects of panel asymmetry generated from the impact damage. The BAI test method may be recommended as an alternative to CAI but quite long specimens are required in order to assure compressive failure in the tested face-sheet, making the test both demanding and expensive. On the other hand, lower load levels are required to break the specimens and there is less need for precise machining during specimen manufacturing. A finite element model including progressive damage evolution was used to estimate the post impact strength. The simulations showed generally good agreement with the experiments. 

Lightweight ice-class vessels offer the possibility of increasing the payload capacity while making them comparable in energy consumption with non-ice-class vessels during ice-free periods. We approach the development of a lightweight hull by dividing ice–hull interactions into quasi-static loading and impact loading phases. Then, investigative outcomes of lightweight concepts for each loading phase may be combined to develop a lightweight ice-going hull. In this study, we focus on the quasi-static loading phase characteristic of thin first-year ice in inland waterways. We investigate metal grillages, sandwich structures and stiffened sandwich structures parametrically using the finite element method. The model is validated using previous experimental studies. In total over 2000 cases are investigated for strength and stiffness with respect to mass. The stiffened sandwich was found to be the most favorable concept that offered both a light weight as well as high gross tonnage. Further, significant parameters and their interactions and material differences for the three structural concepts were investigated and their trends discussed. The outcomes result in the creation of a viable pool of lightweight variants that fulfill the quasi-static loading phase. Together with outcomes from the impact loading phase, a lightweight ice-going hull may be developed.

A simplified numerical model is introduced to predict ice impact force acting on the ship hull in level ice condition. The model is based on ice-hull collision mechanisms and the essential ice breaking characteristics. The two critical ice failure modes, localized crushing and bending breaking, are addressed. An energy method is used to estimate the crushing force and the indentation displacement for different geometry schemes of ice-ship interaction. Ice bending breaking scenario is taken as a semi-infinite plate under a distributed load resting on an elastic foundation. An integrated complete ice-hull impact event is introduced with ice failure modes and breaking patterns. Impact location randomness and number of broken ice wedges are considered in order to establish a stochastic model. The analysis is validated by comparison with the model ice test of a shuttle passenger ferry performed in May 2017 for SSPA Sweden AB at Aker Arctic Technology Inc. Good agreement is achieved with appropriate parameter selection assumed from the model test and when ice bending failure is dominant. This model can be used to predict the ice impact load and creates a bridge between design parameters (ice properties and ship geometry) and structure loads.

The current study focuses on the bearing failure process of NCF composites and associated damage mechanisms. A set of experiments on bolted joints between NCF composite and steel plates have been performed. The bearing damage onset and failure progression in the composite was monitored at different load levels by microscopic image analysis. Fibre kinking in 0 degrees. layers was found as the key damage mechanism that initiates and drive the bearing failure. Matrix cracking and delaminations were found as well. A cost-effective FE model that predicts bolt bearing failure of NCF composites was proposed. The model utilises state-of-the-art failure criteria and predicts both intra- and inter-laminar progressive damage. A good correlation between the predicted damage development process and experiments was observed both in terms of failure modes and load levels.

For ships running on ice-covered waters, the ice impact load on ship structure shall be carefully considered. This paper proposes an analytical model which takes two most important ice failure modes, localized crushing and bending breaking, into consideration. The energy method is introduced to estimate the crushing force and the indentation displacement for different scenarios. Ice bending breaking scenario is simplified as a semi-infinite plate under a distributed load resting on an elastic foundation. The two ice failure modes are assumed to share the same contact area. This model is useful to predict the ice impact load and creates a bridge between design parameters (ice properties and ship geometry) and structure loads. 

This paper deals with the problem of face/core interfacial disbonds in sandwich panels that are pressurised, i.e. the disbond has an initial fluid pressure that causes the disbond to deform. The problem is often referred to as a blister. The panel with a blister is then subjected to an in-plane compressive load. Four different panels are analysed and tested, having different size disbonds and different initial internal pressure. The cases are analysed using a finite element approach where the blister is modelled using fluid elements enabling the pressure inside the blister to vary as the in-plane load is applied. The analysis uses non-linear kinematics, and in each load step, the energy release rate is calculated along the disbond crack front. This model is used for failure load predictions. The four cases are then tested experimentally by filling a pre-manufactured disbond cavity with a prescribed volume of air. This air volume is then entrapped, and the panel is subjected to an in-plane compressive load. The load and blister pressures are measured throughout the test and compared with the finite element analysis. Surface strains and blister deformations are also measured using digital correlation measurements. The predicted failure loads compare well with the experimental results, and so does the blister pressures, the latter at least qualitatively.