Experimental and numerical investigation of fracture in double-edge notched steel plates

Double-edge notched (DENT) steel plates were pulled until complete fracture and several experimental observations were made (using profilometry and scanning electron microscopy). The essential work of fracture (EWF) model was found to be well verified. Numerical simulations—up to the maximum load only—of some experiments were performed using the finite element method (FEM), and incorporating geometric and material non-linearities (large deformation elasto-plasticity). Some experimental measurements were compared with the corresponding numerical computations and excellent agreement was found.     

Mechanical characterization and modeling of the deformation and failure of the highly crosslinked RTM6 epoxy resin

The nonlinear deformation and fracture of RTM6 epoxy resin is characterized as a function of strain rate and temperature under various loading conditions involving uniaxial tension, notched tension, uniaxial compression, torsion, and shear. The parameters of the hardening law depend on the strain-rate and temperature. The pressure-dependency and hardening law, as well as four different phenomenological failure criteria, are identified using a subset of the experimental results. Detailed fractography analysis provides insight into the competition between shear yielding and maximum principal stress driven brittle failure. The constitutive model and a stress-triaxiality dependent effective plastic strain based failure criterion are readily introduced in the standard version of Abaqus, without the need for coding user subroutines, and can thus be directly used as an input in multi-scale modeling of fibre-reinforced composite material. The model is successfully validated against data not used for the identification and through the full simulation of the crack propagation process in the V-notched beam shear test.     

Numerical Modeling of Bolted Lap Joint Behavior

Nonlinear finite-element models are developed that predict the load-elongation behavior of conical-head bolted lap joints, and the load-elongation predictions are compared with experimental test data. The study is conducted for several panel thicknesses with three fastener sizes and three panel materials. The model load-elongation predictions are in excellent agreement with experimental test data. Model parameters, such as part discretization, material model selection, sliding interface friction coefficients, and convergence tolerances, are discussed. A means of inducing clamp in the joint is also developed. The results show that nonlinear finite-element analysis may reliably predict the behavior of conical-head bolted joints.     

Influence of Head Geometry on Bolted Joint Behavior

Numerical models of single-fastener bolted lap joints are developed in which the effect of the head angle and height on joint elongation are studied for three fastener sizes, three panel materials, and several panel thicknesses. Baseline 100° bolt-head angle numerical models are calibrated and validated with experimental data. These baseline models are then modified to predict the load-elongation behavior of lap joints with five different head angles and four different head heights. The numerical predictions are summarized in graphical form. The results show that the fastener head height has a much greater influence on joint-slip resistance than does the angle, with the shallower heads providing the greatest resistance to joint elongation under load.     

Social adjustment and the course of affective illness: a one-year controlled longitudinal study involving bipolar and unipolar outpatients

The association between social adjustment and recurrent affective episodes was examined in 27 recovered bipolar patients and 24 recovered unipolar patients who had been receiving maintenance treatment for at least 1 year. Social adjustment variables and psychiatric status were assessed by bimonthly interviews over the 1-year period using the Social Adjustment Scale (SAS) and the Research Diagnostic Criteria (RDC). Variations in the social adjustment scores were analyzed in the 2 months preceding the onset of a recurrent affective episode. Furthermore, social adjustment variables at entry into the study were assessed to investigate whether there was any association between these and the potential timing of a recurrent episode. Results revealed no significant deterioration in social adjustment during the 2 months preceding a recurrent affective episode. However, it was demonstrated that there was a relationship between a patient's overall social adjustment score at entry into the study and the onset of recurrent affective episodes, independent of any residual depressive symptomatology. Specifically, impaired work adjustment in bipolar and unipolar patients was associated with recurrent episodes. Impaired social and leisure activities adjustment in bipolar patients was also associated with recurrent episodes, and impaired marital adjustment in unipolar patients was associated with recurrent episodes. These results suggest that social maladjustment could be a risk factor for both unipolar and bipolar recurrent affective episodes and that impairment in specific areas of social functioning could be used to predict outcome.     

Application of the CVBEM to non-uniform St. Venant torsion

The complex-variable boundary-element method, or CVBEM, is used to approximate the stress distribution associated with non-uniform St. Venant torsion problems. By specifying either the normal- or tangential-force equilibrium equation in terms of the warping function or its conjugate, a Laplace equation results which is immediately tractable by using the CVBEM. A comparison of modeling results to known solutions indicates that the modeling technique is a useful approach for the estimation of interior stresses as well as for the evaluation of modeling error by means of an approximate boundary determined by the CVBEM approximation function.     

Specific influence of polyethersulfone functionalization on the delamination toughness of modified carbon fiber reinforced polymer processed by resin transfer molding

The specific influence of polyethersulfone (PES) end‐functionalization with chlorine or hydroxyl end groups at same molar mass on PES‐epoxy composites based on a high‐performance tetra‐epoxide with di‐amine hardener resin (RTM6) is investigated in terms of morphology, thermal behavior, and toughness. A model study on PES filaments embedded in epoxy precursor is first performed to compare the interdiffusion and resulting morphology upon curing. PES‐OH shows a larger interdiffusion distance compared to PES‐Cl in the model systems and the laminates. This effect is more pronounced at high heating rate. Cross sections and fracture surfaces of composite panels are analyzed by scanning electron microscopy (SEM) coupled with energy dispersive X‐ray (EDX) spectroscopy to establish the link between the microstructures and fracture mechanisms. The toughness of PES‐OH‐modified epoxy composites is doubled compared to unmodified reference panels, whereas the PES‐Cl shows no improvement. The favorable influence of PES‐OH is ascribed to enhanced miscibility, interfacial adhesion and morphology, resulting from the better affinity between hydroxyl‐terminated PES and the epoxy‐resin. POLYM. ENG. SCI., 59:996–1009, 2019. © 2019 Society of Plastics Engineers