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This study investigates fatigue life and fracture in welded stainless steel 304L (SS 304L) resulting from load-controlled fatigue. This was done for specimens from two welding manufacturers. Mechanical testing was carried out using a MTS test frame in uniaxial tension. Specimens fabricated in 3 weld configurations (butt, lap, butt-with-backer) were cycled at stress ratio R = 0.1, frequency f = 5 Hz, and experienced varying mean tensile stress. A comparison of the fatigue life of welded and unwelded (or pristine) specimens determined that the fatigue life of welded specimens is considerably shorter. The microstructure in the parent material (PM), heat affected (HAZ) and fusion zones (FZ) was analyzed using SEM, and results suggest that, for a limited number of specimens (backer welds), fracture in the (FZ) was primarily the result of Zener-Stroh cracks. Most welded specimens fractured at the weld-HAZ interface (weld toe), and we postulate that stress concentrations primarily due to abrupt geometrical change at the weld interface led to crack initiation there. Additional stress concentrations at welding induced defects (resulting from high temperature) such as second phase particles, fatigue induced defects, and pre-existing impurities are responsible for crack initiation, crack growth, and eventual fracture. Comparison of unwelded and welded SN curve data using numerical curve fitting methods reveal that the fatigue life of pristine SS 304L follows the expected sigmoid shape found in literature (specifically the Chandran fatigue model), while that of welded SS 304L deviates considerably in low cycle fatigue (LCF) and follows the Basquin power law equation.

Epoxy underfills can be implemented in electronic packaging to enhance solder joint reliability of surface mounted components. However, it is important for an engineer to have a failure criterion that can be used for failure predictions and redesign of electronic assemblies. Data from epoxy bond failure in mock electronic part assemblies were correlated to finite element analyses to predict adhesive failure initiation. Experiments were performed to determine failure loads for various loading locations and nonlinear viscoelastic analyses were performed for the same loading locations to determine a maximum principal strain failure parameter. Predictions showed that a maximum principal strain failure parameter defined from one test could be used as an indicator of adhesive failure of an epoxy bond undergoing other modes of loading. Failure initiation predictions matched experimental data using a maximum principal strain failure parameter for an epoxy bond undergoing mixed modes of loading for both unfilled and alumina oxide filled 828DEA epoxy. Such experimental setup is deemed appropriate for future epoxy testing.

Fe-Co-2V (Hiperco equivalent) is a soft ferromagnetic material that is commonly used for electrical components that require robust magnetic performance. Despite the excellent magnetic properties of Fe-Co-2V, it often exhibits low strength, ductility, and workability due to an ordered B2 microstructure. The mechanical properties exhibit considerable dependency on grain size and degree of order, which are influenced by processing methods. A thorough understanding of Fe-Co-2V’s fatigue performance is required to predict mechanical reliability under operating loads; however, limited fatigue data currently exists for Fe-Co alloys. This work characterizes the fatigue properties of wrought Fe-Co-2V through strain-controlled fatigue testing and fractography. Young’s Modulus, ultimate strength, and yield stress were determined through monotonic tension tests. The fatigue behavior was quantified using fully reversed, strain-controlled fatigue testing for applied strain amplitudes ranging from 0.10% to 1.00%. Subsequently, the Coffin-Manson strain-life curve was fit to the experimental data. Failure mechanisms were investigated through fractography with a scanning electron microscope. Inspection of the failure surfaces revealed that crack initiation occurred at defects located on or near the specimen surface with a localized region of crack propagation prior to the transgranular cleavage fracture. Additionally, two material models were calibrated from the experimental static and cyclic experimental testing. The characterization of the fatigue behavior of wrought Fe-Co-2V presented herein will aid in the fatigue analysis of Fe-Co-2V components and the development of analytical fatigue modelling methodologies.

Quantification of the stress field around dislocations is important in dislocation theory and can have profound effect on computations involving dislocations such as in discrete dislocation dynamics (DDD) simulations. In this paper, the original work by Devincre (1995) on the stress field of a linear dislocation segment is carefully studied and based on three regions of space, a physics-based algorithm is presented to treat any singularity, weak or strong, associated with the self-stress of the segment. The paper shows several utilisations of this method. Two of these utilisations concern the 'collocation-point' method for capturing free-surface effects on dislocation forces and movement. In one, an on-the-fly mesh was utilised, and in the other an unstructured mesh was utilised. Results were validated where appropriate and both static and dynamic implementations are presented.

Quasi-static structural finite-element models of an aluminum-framed crystalline silicon photovoltaic module and a glass–glass thin-film module were constructed and validated against experimental measurements of deflection under uniform pressure loading. Specific practices in the computational representation of module assembly were identified as influential to matching experimental deflection observations. Additionally, parametric analyses using Latin hypercube sampling were performed to propagate input uncertainties related to module materials, dimensions, and tolerances into uncertainties in simulated deflection. Sensitivity analyses were performed on the uncertainty quantification datasets using linear correlation coefficients and variance-based sensitivity indices to elucidate key parameters influencing module deformation. Results identified edge tape and adhesive material properties as being strongly correlated to module deflection, suggesting that optimization of these materials could yield module stiffness gains at par with the conventionally structural parameters, such as glass thickness. This exercise verifies the applicability of finite-element models for accurately predicting mechanical behavior of solar modules and demonstrates a workflow for model-based parametric uncertainty quantification and sensitivity analysis. Applications of this capability include the assessment of field environment loads, derivation of representative loading conditions for reduced-scale testing, and module design optimization, among others.

The adhesion of coatings often controls the performance of the substrate-coating system. Certain engineering applications require an epoxy coating on a brittle substrate to protect and improve the performance of the substrate. Interfacial adhesion measurements of such systems provide a quantitative metric of that performance. Indentation experiments were performed to induce interfacial delaminations in a glass substrate-epoxy coating system. Delamination loads and radii were measured and applied to an analytical solution originally developed by Rosenfeld et al. (1990) to estimate the interfacial fracture energy of the substrate-coating adhesive bond. Results suggest an interfacial bond strength far exceeding that of similar previously studied glass-epoxy systems.

Displacement of surgical drains from their intended attachment location can lead, in some cases, to a secondary operation in order to avoid recovery complications. Displacements are usually due to the loosening of a drain's anchoring. The common practice of drain anchoring involves the Roman Sandal technique. This manuscript compares the mechanical behaviour of this conventional drain suturing technique to the modified Roman Sandal technique developed herein. Identical mechanical cyclic tests mimicking breathing action were conducted on both suturing techniques to determine which is more reliable. The obtained results revealed that the modified Roman Sandal technique is a much more reliable when compared to the Roman Sandal technique.

This study investigates, through finite-element analysis, different plate-screw fixation systems used for medial opening proximal tibial osteotomies (locking or non-locking with or without a medial spacer). Sulzer stainless steel non-locking without spacer, Synthes titanium locking without spacer, Smith and Nephew custom titanium locking with a wedge spacer and Arthrex stainless steel non-locking with a wedge spacer fixation systems were modelled and compared. All fixation systems were tested under static loading of 889 N applied evenly over the proximal tibia particular surface. The areas of highest stress experienced in the bone and the plate/screw interface were analysed. Tendency of the osteotomy wedge to close under loading for each fixation system was analysed. The numerical results suggest the titanium locking plate with wedge spacer block outperforms the others by achieving lower stresses (incurred by the fixation system and bone) and loss of correction. Locking screw mechanisms and wedge spacer blocks appear advantageous.

OBJECTIVES To describe a cause of recurrent nasal obstructive symptoms after septoplasties including the creation of a sizable submucous window and to suggest treatments for this complication. METHODS Case report of a woman presenting with side-changing nasal dyspnea approximately 1 year after undergoing septoplasty and engineering analysis of nasal cavity airflow. We created a computer model of the airway, analyzed varying sizes of surgical defects, and optimized the geometry of the submucous window. RESULTS An optimum area of resection to maximize the area of cartilage and/or bone resected and to minimize deflection of the septal area of iatrogenic litheness is a rectangular shape approximately 44 mm long by 12 mm high in our model. CONCLUSIONS A large submucous window can result in obstruction of nasal airflow after septoplasty owing to displacement of this compliant area with respiration under the forces described in the Bernoulli theorem. Treatment may include turbinate reduction and/or septal reconstruction.Arch Facial Plast Surg. 2010;12(6):385-392--

Fatigue failure of threaded distal locking screws used in intramedullary nailing of fractures of the femur is a significant problem. The current study compares fatigue strength of a threaded screw to an unthreaded peg according to generated stresses using the finite element method. The first analysis considered the unthreaded OrthoFix peg. The second analysis modified the peg to include a threaded portion along its length. The boundary conditions simulated include a range of axial loads of 900 N to 2,400 N. The results demonstrate that using a smooth peg versus a threaded screw will increase the fatigue strength by 72%. The peg will last well past the required ten weeks at all of the loads considered. For the screw, a 270 lb. human can expect two weeks of safe fixation before screw breakage while a 202 lb. body can expect only seven weeks of safe fixation.

Bioabsorbable bone plates can eliminate the necessity for a permanent implant when used to fixate fractures of the human mandible. They are currently not in widespread use because of the low strength of the materials and the requisite large volume of the resulting bone plate. The aim of the current study was to discover a minimally invasive bioabsorbable bone plate design that can provide the same mechanical stability as a standard titanium bone plate. A finite element model of a mandible with a fracture in the body region is subjected to bite loads that are common to patients postsurgery. The model is used first to determine benchmark stress and strain values for a titanium plate. These values are then set as the limits within which the bioabsorbable bone plate must comply. The model is then modified to consider a bone plate made of the polymer poly-l/dl-lactide 70/30. An optimization routine is run to determine the smallest volume of bioabsorbable bone plate that can perform and a titanium bone plate when fixating fractures of this considered type. Two design parameters are varied for the bone plate design during the optimization analysis. The analysis determined that a strut style poly-l-lactide-co-dl-lactide plate of 690 mm2can provide as much mechanical stability as a similar titanium design structure of 172 mm2. The model has determined a bioabsorbable bone plate design that is as strong as a titanium plate when fixating fractures of the load-bearing mandible. This is an intriguing outcome, considering that the polymer material has only 6% of the stiffness of titanium.

Plastic deformation in metals is dominated by the interactions among dislocations and other defects inside the crystal. A large number of dislocation multipoles (dipoles, tripoles, quadrupoles, etc.) can form during plastic deformation. Depending on the relative position and the orientation of the dislocations, interactions in and between multipoles can change the elastoplastic properties of a material. The authors of this article investigate the effect of dislocation multipoles on the elastoplastic properties of a material. This is performed analytically under different multipole configurations (i.e., the distance between active glide planes and the signs of the dislocations) as well as using a three-dimensional discrete dislocation dynamics (DDD) code. The simulations show that multipoles exhibit a hardening/softening effect when the sign of the dislocations involved is the same, and a hardening effect only when the dislocations are of opposite sign to nearby ones. The distance between the two neighboring dislocations was also affecting the proportional limit (PL) for the material. Such hardening or flow stress (FS) results, as in this study, can be incorporated into larger-scale modeling work.

This paper serves as an investigation into the response of the NASA space shuttle wing in the event of a debris impact during launch. The explicit finite element method is used to model the leading edge of the shuttle wing and the event of impact with a piece of a material from the shuttle's external tank. The results will be utilised by the Impact Penetration Sensor System (IPSS) to help characterise the signal received by the system in the event of an actual impact. Numerical results are validated by experiments done at the Southwest Research Institute (SwRI).

The effect of irradiation on the microstructure of metals often produces a high number density of dislocation loops, consisting of self-interstitial platelets. In dislocation theory these damage clusters are treated as prismatic dislocation loops. The elastic fields of such loops are solved analytically in the literature typically for loops in an infinite material. Near a free surface this solution is altered by image stresses. This work presents an analytically derived solution for the elastic fields of a sub-surface rectangular dislocation loop in a half material. Resulting surface displacements are compared against Molecular Dynamics (MD) computations for Tungsten.

Paediatric spinal deformities pose much difficulty for orthopaedic surgeons. Halo-gravity traction using threaded stainless steel pins with a graphite halo device mounted to the skull has been successful, but is invasive and must be tailored specifically to each individual patient. Experimental and clinical testing in paediatrics has been performed to evaluate the halo-gravity traction method of correction to optimise required number of pins, and pin-torque loading parameters, with differing results. For paediatrics, surgeons do not apply loading exceeding 50% of a child's body weight. The current study experiments with six and ten pin halo configurations under applied torque loading of 226, 452 and 678 Newton-millimetre (2, 4 and 6 inch-pound) to determine failure loading of the halo system. The results indicate that the failure load of the sawbone skulls far exceeds the average weight of a paediatric patient.

Abstract: This work focuses on an anisotropic elasticity treatment of strain partitioning in planar thin layers/films caused by heteroepitaxial crystal growth. In particular, orthotropic materials are considered here. Previous work mostly focused on isotropic elasticity. Here, under the assumption of plane stress and using Hooke’s law for linear elasticity, equilibrium equations, and typical strain definitions, one obtains a solution for the strains, in the two planar directions, in the substrate and the epilayer. The strains in a particular layer are expressed as a function of the elastic constants, thicknesses, and lattice parameters of both layers. These results show that the anisotropic solution differs considerably from the isotropic treatment. The current results can also be used to predict the onset of misfit dislocation formation.

Abstract: When irradiated, metals undergo significant internal damage accumulation and degradation of mechanical properties. Damage takes the form of a high number density of nanosize defect clusters (stacking-fault tetrahedrons (SFTs) or interstitial loops). The alteration of mechanical properties is manifested in a hardening behavior and localized plastic deformation in defect-free channels. This work uses discrete dislocation dynamics (DD) to capture these effects. It sets the framework for the elastic interaction between gliding dislocations and defect clusters and details a scheme for loop unfaulting and absorption into dislocations. Here, it is shown that SFTs represents weaker pinning points for dislocation motion than parent dislocation loops. It is also shown that appreciable yield drop can be attributed to high density of defects decorating the dislocations. Strong obstacles cause dislocations in Cu to continually double cross slip causing the formation of defect-free channels. Finally, the correlation between yield stress increase and defect number density is in excellent agreement with the experiment.