In packaging, the structural integrity of paperboard under complex stresses is essential. This study examines the delamination behavior of paperboard under normal and shear loading modes, which are the base for developing mixed-mode models. Four commercial paperboard grades, sourced from fibers across three geographical regions, are investigated using Double Cantilever Beam (DCB) and Split Double Cantilever Beam (SDCB) tests, which are used to calibrate a cohesive zone model from the literature. This model introduces a shape parameter that governs the cohesive traction-separation relationship, consistent across both normal and shear modes. Experimental findings support this approach, demonstrating that, while the shape parameter remains mode-independent, its numerical value varies uniquely for each paperboard quality.

Cohesive Zone Models with finite thickness are widely used for the fracture mechanical modeling of material layers, e.g., adhesive layers. Within this approach, the whole layer is modeled as a cohesive zone. Moreover, computational homogenization techniques are crucial for the development of advanced engineering materials, which are often heterogeneous. Compared to the commonly used Finite Element Method (FEM), solvers based on the Fast Fourier Transform (FFT) are expected to reduce the computational effort needed for the homogenization. Originated from an existing method for the computational homogenization of cohesive zones using FEM, a novel FFT-based homogenization scheme for cohesive zone models is presented. Our implementation of the FFT solver uses a displacement-based Barzilai–Borwein scheme and a non-local ductile damage model for the fracture behavior. Finally, the practical application of the method is discussed using an adhesive layer and the core material of HybrixTM metal sandwich plates as examples.

A cohesive interface model based on a master curve is proposed for the analysis of delamination in paperboard under various loading, unloading, and reloading conditions. The model is thermodynamically consistent and considers the effects of elasticity, plasticity, and damage. The proposed model is verified by comparing its predictions with experimental data obtained from multiple loading–unloading–reloading cycle experiments using a split double cantilever beam specimen. The results show that the model can predict the cyclic behavior of shear loading and provide insight into the damage evolution associated with different loading paths by analyzing the shear stress distribution in the fracture process zone. The model's calibration process requires monotonic normal and shear loading data but only cyclic normal loading data. Additionally, the model accounts for the paperboard's fiber–fiber friction and normal dilatation due to shear loading. In total, nine parameters are needed to calibrate the model.

Cohesive Zone Models with finite thickness are widely used for the fracture mechanical modeling of layers of material, e.g., adhesives. Within this approach, the whole layer is modeled as a Cohesive Zone. Moreover, computational homogenization techniques are crucial for the development of advanced engineering materials, which are often heterogeneous. Compared to the classical Finite Element Method (FEM), computationally more efficient solvers based on the Fast Fourier Transform (FFT) are expected to reduce the computational effort needed for the homogenization. Originated from an existing method for the computational homogenization of Cohesive Zones using FEM, a novel FFT-based homogenization scheme for Cohesive Zone Models was developed. Our implementation of the FFT solver uses the Barzilai-Borwein scheme and a non-local ductile damage model for the fracture behavior. Finally, the method is applied to the core material of HybrixTM metal sandwich plates, and the good agreement with experimental results in opening mode I is shown.

An experimental study to characterize properties controlling delamination of paperboard is presented. The normal and shear traction–separation laws are measured and evaluated using a double cantilever beam (DCB) and a split double cantilever beam (SCB) specimen. The DCB-experiments provides normal separation data in good agreement with results using alternative experimental techniques. From the measured data, both normal and shear fracture resistance data are obtained. A length parameter is introduced. The length parameter allows for the cohesive law to be obtained from a dimensionless master curve which is valid both for normal and shear loading. Taking advantage of the master curve, a mixed-mode potential is proposed. The mixed-mode potential is implemented as a user interface to a finite element code. As a final test, the experimental setups of the DCB and SCB specimens are simulated to validate the identified normal and shear properties.

High-quality simulation methods demand accurate material models. In simulations an adhesive can be represented by a cohesive layer. A cohesive layer model utilizes a cohesive law to represent the homogenized mechanical behaviour of a layer with a thickness. In the current paper we use three experimental methods to measure the cohesive law in shear using the ENF-specimen; one of the methods is novel and is also useful for evaluation of experiments with the ELS-specimen. Two sets of experiments are performed, one with elastic substrates and one with plastically deforming substrates. Each experiment is evaluated using all three methods. The evaluation shows that all methods provide reasonable data; the results are similar if the substrates are elastic. With smaller specimens, the substrates deform plastically and one of the methods is identified as the most accurate.

Pressure sensitive adhesives provide beneficial properties for bi-material bonding and we here focus on influences of the loading rate. The cohesive law for a tape is measured using the J-integral method. In-situ studies of the fracture process are made. The fracture energy and cohesive law levels off below an engineering strain rate of about 2s(-1). All the cohesive laws include two peak stresses, the first is associated with nucleation of cavities and occurs at a stress level comparable to the critical stress for cavitation in rubber. The second peak stress occurs just before final fracture when walls formed between the cavities break down. Slower rates give more time for cavities to nucleate. A similarity of the effects of loading rate and ageing is also identified.

Confined layers may fracture in shear. This occurs, for example in adhesive joints and composite materials. A common mechanism for shear fracture is the formation of shear hackles associated with an expansion of the layer. This makes shear toughness and strength depend on the constraint of the expansion. By constraining the expansion using external loading in experiments, the expansion is reduced but not totally inhibited. The experiments are evaluated using the path independent properties of the J-integral. It is shown that the shear toughness increases for the more constrained case. Thus, from a strength analysis perspective, ignoring the expansion leads to a conservative estimate of the fracture properties. Extrapolation of the evaluated properties to totally inhibited expansions gives the traction separation relation and the fracture toughness for a layer in simple shear.

Performance-related bonuses are important tools for investment organizations to incentivize stock traders. Yet, two experiments indicate that bonuses rewarding short-term performance may lead to worse timing of purchases. The authors propose that hyperbolic time discounting makes participants set lower aspired purchase prices for short-term (decreasing percentage) bonuses than for long-term (increasing percentage) bonuses. For this reason purchases are made earlier for decreasing than increasing percentage bonuses, earlier for decreasing than random prices, and earlier for high price volatility than for low price volatility. Neither purchases at the lowest price or highest bonus are attained. Hyperbolic time discounting may account for bubbles observed in experimental double-auction markets.

The stress-deformation relation i.e. cohesive law representing the fracture process in an almost incompressible adhesive tape is measured using the double cantilever beam specimen. As in many ductile materials, the fracture process of the tape involves nucleation, growth and coalesce of cavities. This process is studied carefully by exploiting the transparency of the used materials and the inherent stability of the specimen configuration. Utilising the path independence of the J-integral, the cohesive law is measured. The law is compared to the results of butt-joint tests. The law contains two stress peaks—the first is associated with nucleation of cavities at a stress level conforming to predictions of void nucleation in rubber elasticity. The second stress peak is associated with fracture of stretched walls between fully-grown cavities. After this second peak, a macroscopic crack is formed. The tape suffers at this stage an engineering strain of about 800%. A numerical analysis with the determined cohesive law recreates the global specimen behaviour.

The theme of the 37th Risø International Symposium is the scientific basis for understanding the performance of composite materials. Specifically, the Symposium focuses on the underlying mechanisms that control the properties of composites, which will lead to better and more reliable model predictions. This will serve to support and further promote the technological development of composite solutions.

The use of MgO-paste as bone cement was tested on titanium cylinders implanted into rat tibia. The evaluation of bone healing was made with the retention force (pull-out) test, light microscopy and ESEM/EDX. Preimplantation of the MgO-paste into drill perforations of rat tibia increased the retention of the titanium implant 6-fold. The error was expressed as the 95% confidence interval of means (n = 10 bones in each group). The observed difference between 3.46+/-0.71 N/mm(2) for Ti-cylinders implanted with MgO-paste and 0.56+/-0.26 N/mm(2) for Ti-cylinders implanted directly into the bone, is statistically significant (p < 0.01). The increase of retention force, caused by MgO is parallel to an increased thickness of the compact bone surrounding the implant and closer contact between bone and implant.Histological examination of the implant-related bone showed that the MgO-induced bone growth is mediated by the formation of a bone-inducing matrix. The matrix contains organic substance, most likely proteins.(C) 2016 Elsevier Ltd. All rights reserved.

Composite materials in wind turbines are mainly joined with adhesives. Adhesive joining is preferable since it distributes the stresses over a larger area. This study shows how a defect can influence the fracture behaviour of adhesively joined composite. Repeated experiments are performed using double cantilever beam specimens loaded with bending moments. The specimens consist of two 8 mm thick GFRP-laminates which are joined by a 3 mm thick epoxy adhesive. A thin foil close to one of the laminates is used to start the crack. For some of the specimens a defect is created by an initial load-unload operation. During this operation, a clamp is used in order to prevent crack propagation in the main direction. For the specimens without defect, the crack propagates in the middle of the adhesive layer. For the specimens with defect, the crack directly deviates into the laminate. After about 25 mm propagation in the laminate, the crack returns to the adhesive. Compared to the adhesive the fracture energy for the laminate is significantly higher.

Structural tapes provide comparable toughness as structural adhesives at orders of magnitude lower stresses. This is potentially useful to minimize the effects of differences in thermal expansion in the joining of mixed materials. The strength properties are modelled using the cohesive zone model. Thus, a cohesive zone represents the tape, i.e. stresses in the tape are transmitted to the substrates through tractions determined by the separations of the surfaces of substrates. This simplification allows for structural analysis of large complex structures. The relation between the traction and the separation is measured experimentally using methods based on the path independence of the J-integral. Repeated experiments are performed at quasi-static loading. A mixed mode cohesive law is adapted to the experimental data. The law is implemented as a UMAT in Abaqus. Simulations show minor thermal distortions due to thermal loading and substantial structural strength in mechanical loading of a mixed material structure.

An existing experimental method to determine cohesive laws for adhesive layers loaded in shear is further developed. The method is based on differentiation of the energy release rate (ERR) with respect to the adhesive shear deformation at the crack tip. The test geometry used is an ENF-specimen for which the adherends are assumed to deform linearly elastic. The original method is expanded to account for situations where the thickness of the adhesive layer is not negligible as compared to the adherend thickness. To this end, a novel mathematical expression for the energy release rate (ERR) is derived. No assumptions on the form of the cohesive law are made; it is implicitly included in the derivation. The expression for the ERR contains the applied load and the shear deformation of the adhesive layer at the initial position of the crack tip, in addition to geometrical properties and the elastic modulus of the adherend material. Numerical simulations are performed to verify the accuracy of the mathematical expression for the ERR. Preliminary results from experiments performed on an epoxy adhesive are presented. The cohesive law of the adhesive layer is extracted by using a blunted crack tip. Verifying simulations confirm that the local pre-fracture behavior is accurately captured.

Our aim is to investigate whether bonuses make stock portfolio managers take higher risks by diversifying less. In two experiments with undergraduates role-playing being professional investors, we test a model implying that they initially anchor on 100% allocation to one of two options delivering the largest bonus payout, then adjust towards allocating equally much to each option (maximal diversification) depending on the degree of perceived uncertainty of the bonus outcome. In Experiment 1 we find as expected that when the bonus is reduced, investment in the preferred option decreases such that diversification increases. Diversification is larger when uncertainty of the bonus outcome is made salient. In Experiment 2 we show that a majority herd strengthens the effect of a bonus for investing in a preferred option despite salient uncertainty of the bonus outcome. In actual stock markets such herding effects would result from investors being similarly rewarded by bonuses.

Sammantaget ser vi inget i motdebattorernas argument som talar emot att infora styrmedel, till exempel konsumtionsskatter, inom dessa omraden dar inga stora tekniska losningar finns i sikte, skriver 14 miljo- och energiforskare i slutrepliken till sin text om flyg- och kottskatt (26/2).

Constitutive data are needed at extreme strains to increase the understanding of fracture processes. Ordinary tensile tests ends prematurely due to localization and large amounts of elastic energy stored in the specimens prior to fracture. A novel method is proposed to perform tensile tests using a double cantilever beam specimen. To verify the method a large specimen is developed and tested. Similar results are achieved with the present method as with more standardized methods giving confidence in the method. The specimen should be possible to minimise to provide data with small specimens.

Svenskarnas globala utslapp fran kottkonsumtion och flygresor motsvarar halften av de totala utslappen pa hemmaplan. I var rapport till ­Naturvardsverket foreslar vi tydliga styrmedel – som nya skatter – for att begransa konsumtionen pa dessa omraden, skriver 14 miljo- och energiforskare.