Reliability-based design optimization of composite stiffened panels in post-buckling regime

This paper focuses on Deterministic and Reliability Based Design Optimization (DO and RBDO) of composite stiffened panels considering post-buckling regime and progressive failure analysis. The ultimate load that a post-buckled panel can hold is to be maximised by changing the stacking sequence of both skin and stringers composite layups. The RBDO problem looks for a design that collapses beyond the shortening of failure obtained in the DO phase with a target reliability while considering uncertainty in the elastic properties of the composite material. The RBDO algorithm proposed is decoupled and hence separates the Reliability Analysis (RA) from the deterministic optimization. The main code to drive both the DO and RBDO approaches is written in MATLAB and employs Genetic Algorithms (GA) to solve the DO loops because discrete design variables and highly nonlinear response functions are expected. The code is linked with Abaqus to perform parallel explicit nonlinear finite element analyses in order to obtain the structural responses at each generation. The RA is solved through an inverse Most Probable failure Point (MPP) search algorithm that benefits from a Polynomial Chaos Expansion with Latin Hypercube Sampling (PCE-LHS) metamodel when the structural responses are required. The results led to small reductions in the maximum load that the panels can bear but otherwise assure that they will collapse beyond the shortening of failure imposed with a high reliability

Multi-fidelity robust design optimisation for composite structures based on low-fidelity models using successive high-fidelity corrections

In this paper, a novel multi-fidelity modelling-based optimisation framework is developed for the robust design of composite structures. The proposed framework provides significant savings on computation time compared to both conventional multi-fidelity and high-fidelity modelling methods while maintaining an acceptable level of accuracy. Artificial neural networks (ANNs) and multi-level optimisation approach are both incorporated into this multi-fidelity modelling formulation. The framework utilises varied High-Fidelity Model (HFM) and LowFidelity Model (LFM) covering different design spaces. This means that the HFM has only a few design variables, whereas the LFM explores the entire design spaces during the optimisation process. The proposed multi-fidelity formulation is demonstrated by the Robust Design Optimisation (RDO) of a mono-stringer stiffened composite panel considering design uncertainty under non-linear post-buckling regime

Multi-fidelity probabilistic optimisation of composite structures under thermomechanical loading using gaussian processes

A multi-fidelity probabilistic optimisation method for the design of composite structures subjected to thermomechanical loading isintroduced in this work for the first time. The proposed multi-fidelity approach offers considerable computation efficiency as well as sufficient accuracy, enabling probabilistic optimisation to include more design variables in the early design phase. This approach incorporates both nonlinear information fusion algorithms and multi-level optimisation to achieve increased accuracy and computation time savings. In this optimisation process, a High-Fidelity Model (HFM) covers only a part of the entire design space with information collected uniformly while providing high-fidelity information of other design spaces sparsely without causing extra computational cost. Simultaneously, a Low-Fidelity Model (LFM) explores the whole design space to compensate lack of high-fidelity information. In this manner, the number of high-fidelity information to construct a multi-fidelity model is dramatically reduced. The Reliability-Based Design Optimisation (RBDO) demonstrated the proposed multi-fidelity method of a mono-stringer stiffened composite panel under thermomechanical loading using Gaussian Processes (GPs

Pseudo-ductile failure mechanism introduced into finger jointed thermoplastic PES interleaved CFRC

Pre-cut unidirectional carbon fibre prepreg composites, with an overlapped finger-joint architecture, were modified through the addition of polyethersulfone (PES) interleaves. The properties arising from these finger-jointed configurations were strongly dependent on the interply overlap region. When the tough thermoplastic interleaves spanned only the central portion of the overlap, a crack arresting failure mechanism was observed in tension. A pronounced plateau region or pseudo-ductile response was shown in conjunction with a strain hardening response after crack arrest. The local strain-to-failure of PES interleaved samples was ~3.2%, an increase of 85% compared to the pre-cut baseline (strain-to-failure 1.6%, pre-cut specimens without interleaves)

Crack arrest in finger jointed thermoplastic interleaved CFRC

Pre-cut unidirectional carbon fibre prepreg (M21/194/34%/T800S) composites were tested in tension with a 20 mm overlapped finger joint architectures. In between the overlapping finger jointed region the effect of introducing polyethersulfone (PES) interleaves is investigated. Samples with the addition of a thick PES interleave arrested the initial crack which formed at the pre-cut site. The strain-to-failure of the thick PES interleaved samples was over 3.2%, an increase of 85% compared to the baseline samples, and catastrophic failure was delayed in the majority of instances

Complex interactions between commercial and noncommercial drivers of illegal trade for a threatened felid

Illegal trade and human-wildlife conflict are two key drivers of biodiversity loss and are recognized as leading threats to large carnivores. Although human-wildlife conflict involving jaguars (Panthera onca) has received significant attention in the past, less is known about traditional use or commercial trade in jaguar body parts, including their potential links with retaliatory killing. Understanding the drivers of jaguar killing, trade and consumption is necessary to develop appropriate jaguar conservation strategies, particularly as demand for jaguar products appears to be rising due to Chinese demand. We interviewed 1107 rural households in north-western Bolivia, an area with an active history of human–jaguar conflict, which has also been at the epicentre of recent jaguar trade cases. We collected information on participants' experiences with jaguars, their jaguar killing, trading and consuming behaviours and potential drivers of these behaviours. We found that the relationships between local people and jaguars are complex and are driven largely by traditional practices, opportunism, human–jaguar conflict and market incentives from foreign and domestic demand, in the absence of law awareness and enforcement. Addressing jaguar trade and building human–jaguar coexistence will require a multifaceted approach that considers the multiple drivers of jaguar killing, trade and consumption, from foreign and local demand to human–jaguar conflict

Complex interactions between commercial and noncommercial drivers of illegal trade for a threatened felid

Illegal trade and human-wildlife conflict are two key drivers of biodiversity loss and are recognized as leading threats to large carnivores. Although human-wildlife conflict involving jaguars (Panthera onca) has received significant attention in the past, less is known about traditional use or commercial trade in jaguar body parts, including their potential links with retaliatory killing. Understanding the drivers of jaguar killing, trade and consumption is necessary to develop appropriate jaguar conservation strategies, particularly as demand for jaguar products appears to be rising due to Chinese demand. We interviewed 1107 rural households in north-western Bolivia, an area with an active history of human–jaguar conflict, which has also been at the epicentre of recent jaguar trade cases. We collected information on participants' experiences with jaguars, their jaguar killing, trading and consuming behaviours and potential drivers of these behaviours. We found that the relationships between local people and jaguars are complex and are driven largely by traditional practices, opportunism, human–jaguar conflict and market incentives from foreign and domestic demand, in the absence of law awareness and enforcement. Addressing jaguar trade and building human–jaguar coexistence will require a multifaceted approach that considers the multiple drivers of jaguar killing, trade and consumption, from foreign and local demand to human–jaguar conflict