. Developments on the 'RESS' element were motivated by the following reasons: first, solid-shell elements automatically incorporate the normal stress along the thickness direction, which makes them more suitable for the simulations with double-sided contact than their shell counterparts; second, they have only translational degrees of freedom, which alleviates some difficulties associated with formulating complex shell formulations using nodal rotations; third, general constitutive models can be used and a reformulation for plane-stress conditions is not necessary. was developed for one single-layer shell structure with reduced in-plane and multiple integration points along the thickness direction of the shell. The formulation consists of several combinations of well-known techniques to ameliorate locking problems as is the case of the enhanced assumed strain (EAS) method. However, the proposed 'RESS' solid shell did not consider the transverse shear components of hourglass (or physical stabilization) parts. This negligence produces a slightly flexible behavior of the element, but it can also cause the appearance of hourglass modes for several non-linear applications including large rigid body rotations. Sometimes, the negligence brings a non-positive-definite status on the stiffness matrix. In order to overcome such drawbacks, a modified assumed natural strain (ANS) method considering the top and bottom surfaces of the element was incorporated for the transverse shear components. At the same time, new hourglass strains for the membrane field were constructed based on the stabilization vectors of Liu et al. (Comput. Meth. Appl. Mech. Engng 1998; 154:69). With these modifications, the improved element (called 'M-RESS') passes both the membrane and bending patch tests and performs with remarkable stability and accuracy in sheet-forming simulations.

SUMMARYIn this work the recently proposed Reduced Enhanced Solid-Shell (RESS) finite element, based on the enhanced assumed strain (EAS) method and a one-point quadrature integration scheme, is extended in order to account for large deformation elastoplastic thin-shell problems. One of the main features of this finite element consists in its minimal number of enhancing parameters (one), sufficient to circumvent the well-known Poisson and volumetric locking phenomena, leading to a computationally efficient performance when compared to other 3D or solid-shell enhanced strain elements. Furthermore, the employed numerical integration accounts for an arbitrary number of integration points through the thickness direction within a single layer of elements. The EAS formulation comprises an additive split of the Green-Lagrange material strain tensor, making the inclusion of nonlinear kinematics a straightforward task. A corotational coordinate system is used to integrate the constitutive law and to ensure incremental objectivity. A physical stabilization procedure is implemented in order to correct the element's rank deficiencies. A variety of shell-type numerical benchmarks including plasticity, large deformations and contact are carried out, and good results are obtained when compared to well-established formulations in the literature.

SUMMARYAccuracy and efficiency are the main features expected in finite element method. In the field of loworder formulations, the treatment of locking phenomena is crucial to prevent poor results. For threedimensional analysis, the development of efficient and accurate eight-node solid-shell finite elements has been the principal goal of a number of recent published works. When modelling thin-and thickwalled applications, the well-known transverse shear and volumetric locking phenomena should be conveniently circumvented. In this work, the enhanced assumed strain method and a reduced in-plane integration scheme are combined to produce a new eight-node solid-shell element, accommodating the use of any number of integration points along thickness direction. Furthermore, a physical stabilization procedure is employed in order to correct the element's rank deficiency. Several factors contribute to the high computational efficiency of the formulation, namely: (i) the use of only one internal variable per element for the enhanced part of the strain field; (ii) the reduced integration scheme; (iii) the prevention of using multiple elements' layers along thickness, which can be simply replaced by any number of integration points within a single element layer. Implementation guidelines and numerical results confirm the robustness and efficiency of the proposed approach when compared to conventional elements well-established in the literature.

a b s t r a c tThis work compares the mechanical performance of agglomerated cork against synthetic materials typically used as impact energy absorbers. Particularly, the study will focus on the expanded polystyrene (EPS) and expanded polypropylene (EPP).Firstly, quasi-static compression tests are performed in order to assess the energy storage capacity and to characterize the stress-strain behavior cellular materials under study. Secondly, guided drop tests are performed to study the response of these materials when subjected to multiple dynamic loading (two impacts). Thirdly, finite element analysis (FEA) is carried out in order to simulate the compressive behavior of the studied materials under dynamic loading.Results show that agglomerated cork is an excellent alternative to the synthetic materials. Not only for being a natural and sustainable material but also for withstanding considerable impact energies. In addition, its capacity to keep some of its initial properties after loading (regarding mechanical properties and dimensions) makes this material highly desirable for multiple-impact applications.

The last decade has seen considerable interest in flexible forming processes. Among the upcoming flexible forming techniques, one that has captured a lot of interest is Single Point Incremental Forming (SPIF), where a flat sheet is incrementally deformed into a desired shape by the action of a tool that follows a defined toolpath conforming to the final part geometry. Research on SPIF in the last ten years has focused on defining the limits of this process, understanding the deformation mechanics and material behavior and extending the process limits using various strategies. This paper captures the developments that have taken place over the last decade in academia and industry to highlight the current state of the art in this field. The use of different hardware platforms, forming mechanics, failure mechanism, estimation of forces, use of toolpath and tooling strategies, development of process planning tools, simulation of the process, aspects of sustainable manufacture and current and future applications are individually tracked to outline the current state of this process and provide a roadmap for future work on this process.

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This paper focuses on the development of a new class of eight-node solid ®nite elements, suitable for the treatment of volumetric and transverse shear locking problems. Doing so, the proposed elements can be used ef®ciently for 3D and thin shell applications. The starting point of the work relies on the analysis of the subspace of incompressible deformations associated with the standard (displacement-based) fully integrated and reduced integrated hexahedral elements. Prediction capabilities for both formulations are de®ned related to nearly-incompressible problems and an enhanced strain approach is developed to improve the performance of the earlier formulation in this case. With the insight into volumetric locking gained and bene®ting from a recently proposed enhanced transverse shear strain procedure for shell applications, a new element conjugating both the capabilities of ef®cient solid and shell formulations is obtained. Numerical results attest the robustness and ef®ciency of the proposed approach, when compared to solid and shell elements well-established in the literature.

a b s t r a c tCork is a natural cellular material capable of withstanding considerable amounts of energy and exhibiting a viscoelastic return to its original shape. This feature is particularly interesting to resist to successive impacts. In this study, the behavior of different types of agglomerated cork (AC) and expanded cork (EC) is investigated under static and dynamic loadings. Double impact was carried out on the samples using a hemispheric actuator. The peak acceleration data for all compounds were further analyzed. Static compression tests gave an interesting insight into the stress-strain curve of agglomerates and Poisson's ratio variation during deformation. Results demonstrate a clear influence of agglomerated density and grain size on the resulting mechanical properties and point out a tremendous potential for this sustainable material to be tailored to fit diverse crashworthiness applications.