Residual Compression Research Articles

Image-enhanced modelling of residual compressive after impact strength in laminated composites

This study implements key mechanisms and parameters observed from the previous compression after impact (CAI) experimental studies into finite element models, to study their effects parametrically on residual compression strength. The mechanisms and parameters include: impact damage area, the role of intact interfaces within the overall damaged region (identified here as the “undamaged cone”), interlaminar toughness, and the extent of permanent out-of-plane deformation. The findings highlight that within the limits observed experimentally, in addition to the size of the damaged area, interlaminar toughness and the extent of permanent out-of-plane deformation strongly affect CAI strength (by up to ∼100% for a given damage area), with toughness playing a more significant role than permanent out-of-plane deformation. For the first time, and contrary to much of the literature, the significant role of the undamaged cone is evidenced and quantified.

Equilibrium phases of dipolar lattice bosons in the presence of random diagonal disorder

Ultracold gases offer an unprecedented opportunity to engineer disorder and interactions in a controlled manner. In an effort to understand the interplay between disorder, dipolar interaction and quantum degeneracy, we study two-dimensional hard-core dipolar lattice bosons in the presence of on-site bound disorder. Our results are based on large-scale path-integral quantum Monte Carlo simulations by the Worm algorithm. We study the ground state phase diagram at fixed half-integer filling factor for which the clean system is either a superfluid at lower dipolar interaction strength or a checkerboard solid at larger dipolar interaction strength. We find that, even for weak dipolar interaction, superfluidity is destroyed in favor of a Bose glass at relatively low disorder strength. Interestingly, in the presence of disorder, superfluidity persists for values of dipolar interaction strength for which the clean system is a checkerboard solid. At fixed disorder strength, as the dipolar interaction is increased, superfluidity is destroyed in favor of a Bose glass. As the interaction is further increased, the system eventually develops extended checkerboard patterns in the density distribution. Due to the presence of disorder, though, grain boundaries and defects, responsible for a finite residual compressibility, are present in the density distribution. Finally, we study the robustness of the superfluid phase against thermal fluctuations.

Gaz Diffusion Layers from functional carbon materials for fuel cells used in energy installations

Gas Diffusion Layers (GDL) for fuel cells are two-dimensional carbon materials designed to obtain a smaller thickness, greater bending stiffness, lower residual deformation and lower compressibility compared to analogs. To produce it, functional carbon materials were used: activated carbon of own production, from vegetable raw materials, acetylene black and single-walled Tuball nanotubes. Dependence on the amount of binder is shown, as are the properties of electrodes made by calendering. The resistance of the rolled electrodes is much lower than that of the sputtered electrodes. There are proposed 4 variants of electrodes, which can be used in fuel cells and are used in power energy installations.

Cyclical fatigue of annealed and of thermally tempered soda-lime-silica glass

We present experimental and theoretical investigations on the cyclic fatigue of annealed and of thermally tempered soda-lime-silica glass. Static fatigue due to subcritical crack growth at micro cracks significantly decreases the macroscopic strength of soda-lime-silica glass and causes a time-dependent strength reduction. A subsequent thermal tempering process is typically used to induce residual surface compression stresses, which inhibit the crack growth of surface cracks, and corresponding bulk tension stresses. From the experimental results we show that the existing models for static fatigue used in linear elastic fracture mechanics can be used for the lifetime prediction of cyclically loaded annealed glass and thermally tempered glass, although the (static) crack growth exponent slightly decreases in cyclic loading. The equivalent duration of tensile stress at the crack tip of a micro crack governs the crack growths and not the number of cycles. The threshold for subcritical crack growth determined from the cyclic experiments was found to be in good agreement with data from literature. But unlike in strength tests with singular and quasi-static re-loading, it could be found that periodic loading with load free intervals does not lead to a strength increase by crack healing effects. Based on the results, an engineering design concept for cyclically loaded glass is presented.

An improved model to describe the repeated loading-unloading in compression of cellular materials

Cellular materials, often referred as foams or structural foams when used for energy absorption, are largely used to protect people and goods in the case of shocks and impacts. The detailed knowledge of their behavior is fundamental to design components for this aim.Peroni et al. (2008)-(2009) proposed a model able to describe the mechanical compression behavior of some polymeric material. Such model, based on the work by Rusch (1970), described the stress-strain curve as a sum of two contributions, the first for the elastic part and the second for the densification. More recently Avalle and Belingardi (2018) presented a more general model where the stress is calculated as a sum of three terms, one for the elasto-plastic phase, the second for the plateau, and a third for the densification. The model could include effects like density and strain-rate.However, those models allow to describe only the monotonic compression behavior: in several situations repeated impacts can happen with unloading followed by further reloading. Unfortunately unloading cannot be described by a linear relation between stress and strain (as is usually considered for metals). Unloading follows a non-linear law with a variable relation between stress and strain in the successive cycles: this requires a particularly complex model.In this work, a new model able to effectively reproduce the compression behavior of some polymeric cellular materials is presented. The model is validated and tuned on the basis of experimental tests with specimen subject to complex cycles of repeated loading and unloading. The model describes both the loading from different levels of residual compression and unloading from any value of compression level. The application to several materials justifies the generality of the method.

Residual capacity of fire exposed light gauge steel frame walls

Light gauge Steel Frame (LSF) walls made of cold-formed steel stud and track sections and lined with gypsum plasterboards are commonly used in buildings as load bearing members. During fire events, gypsum plasterboards act as a thermal barrier and delay the temperature rise in the steel studs. Fire usually occurs on one side of LSF walls during which a non-uniform temperature distribution is developed across the steel stud cross-section. This results in thermal bowing deformations and non-uniform distribution of strength and stiffness within the studs. In most situations, fires are extinguished well before excessive or permanent plastic deformations of studs and/or stud failures occur. Hence the LSF wall frames could be re-used provided their residual capacities after fire events are adequate. This paper presents a study aimed at determining the residual compression capacities of LSF wall studs following fire exposure. A full scale standard fire test of LSF wall panel was conducted first, followed by a series of short column tests of lipped channel studs obtained from the tested LSF wall panel. Finite element analyses of the tested studs were undertaken using the measured post-fire mechanical properties of cold-formed steels. The residual compression capacities of these fire exposed short columns were also predicted using the ambient temperature cold-formed steel design rules. A numerical parametric study was then undertaken for 3m long studs in LSF wall panels with varying wall configurations following an exposure to standard fire. This paper presents the details of these experimental and numerical studies of fire exposed LSF wall panels and the results. It demonstrates the potential of re-using LSF wall frames following fire exposures and provides appropriate limits for fire exposure time and stud hot flange temperature for three commonly used LSF wall configurations.

Treatment of Paget-Schroetter syndrome with a three-stage approach including thoracoscopic rib resection at the second stage.

Young, active persons may suffer lifelong consequences of subclavian vein thrombosis, but the best treatment options remain unclear. On introduction of more active pharmacomechanical thrombus removal and thoracoscopic rib resection in our institution, we planned a diagnostic and treatment protocol and aimed to analyze the early, midterm, and intermediate-term results. The study included 72 patients who were diagnosed with an upper limb deep venous thrombosis and underwent phlebography between 2006 and 2013. After the initial treatment, control phlebography was performed and a thoracoscopic first rib resection was considered. Postoperative balloon angioplasty was performed when appropriate, and 1-year follow-up phlebography was carried out. After the initial thrombus removal, 60 patients were treated with thoracoscopic first rib resection and subsequent phlebography with or without balloon angioplasty. The median time from symptom to surgery was 124days, and six (10%) patients had a reocclusion before surgery. Ten (16.7%) patients experienced complications, which were treated mainly with a chest tube (n= 3) or thoracoscopic re-exploration (n= 4). Three months after surgery, 98.3% (59/60) experienced an overall relief of symptoms. No recurrence of clinical thrombosis or residual compression due to incomplete rib resection was seen, and 96.6% (56/58) of the patients reported an overall improvement of symptoms at 13months. Two patients (3.4%) were treated for chronic pain and had electroneuromyography-verified nerve plexus damage. In both cases, the pain was relieved in the long run. A combination of early thrombus removal, thoracoscopic first rib resection, and postoperative venous balloon angioplasty seems to yield acceptable intermediate-term results after Paget-Schroetter thrombosis.

2D-RBUC for efficient parallel compression of residuals

In this paper, we present a method for lossless compression of residuals with an efficient SIMD parallel decompression. The residuals originate from lossy or near lossless compression of height fields, which are commonly used to represent models of terrains. The algorithm is founded on the existing RBUC method for compression of non-uniform data sources. We have adapted the method to capture 2D spatial locality of height fields, and developed the data decompression algorithm for modern GPU architectures already present even in home computers. In combination with the point-level SIMD-parallel lossless/lossy high field compression method HFPaC, characterized by fast progressive decompression and seamlessly reconstructed surface, the newly proposed method trades off small efficiency degradation for a non negligible compression ratio (measured up to 91%) benefit.

A procedure and device for calibration-free determination of residual compression stresses in low-carbon steels deformed by tension

A procedure for determining the residual compression stresses in tension-deformed low-carbon steels has been proposed that does not involve pre-calibration of the device with standard samples for the case where magnetic anisotropy is mainly determined by mechanical compression stresses. A new design of the attachable measuring transducer is presented for experimental determination of the induced magnetic-anisotropy field within local areas of lump ferromagnetic objects. The legitimacy of evaluating compression stresses with this procedure has been proved experimentally.

Posterior Cervical Keyhole Foraminotomy in Treatment of Cervical Radiculopathy Following Anterior Cervical Discectomy and Fusion

Background Data: Cervical radiculopathy after prior anterior cervical discectomy may result from residual compression after the first surgery or development of new compression at the same level or an adjacent level. Treatment for recurrent or residual symptoms can involve conservative measures or surgery. The anterior approach may be used with ease for the treatment of fresh level disc disease although it may be difficult in recurrent or residual situations.Purpose: To describe the surgical outcome of posterior keyhole foraminotomy with or without discectomy for treatment of cervical radiculopathy following anterior cervical discectomy and fusion (ACDF).Study Design: Retrospectively analysis of a prospectively collected database of a consecutive series of patients.Patients and Methods: We included patients that had undergone microscopic posterior cervical keyhole foraminotomy with or without discectomy surgeries for residual or recurrent cervical radiculopathy after prior ACDF. Patients with central canal compression were excluded. The site of recurrence and outcome after surgery has been reported and correlated with the procedure performed. The clinical outcome was evaluated by pain Visual Analogue Score (VAS), Neck Disability Index (NDI) and Oswestry Disability Index (ODI). Postoperative complications were reported. Chi-Square or Fisher exact test was used to compare categorical variables and Mann–Whitney U test was used to compare continuous variables.Results: we identified twenty-one patients who had 24 posterior cervical keyhole foraminotomies (18 single and 3 double level) after prior anterior cervical discectomy and fusion (19 single and 2 double level) through 2013 to 2016. In 12 patients (57%), the complaint was related to the primary level, of whom 3 patients had additional level to the primary one. Nine patients (43%) had a complaint related to the new disc level other than the primary level of surgery. The clinical outcome was generally satisfactory, where pain VAS, Neck Disability Index (NDI) and Oswestry Disability Index (ODI) were significantly reduced after surgery. Eighteen (85.7%) patients had an excellent or good clinical outcome. Two patients had wound infection and one patient had wound hematoma, all treated conservatively. No neurologic deficit has resulted from the posterior cervical keyhole foraminotomy. No postoperative mortality. No recurrence of symptoms has been reported trough the period of follow up.Conclusion: Microscopic posterior cervical keyhole foraminotomy with or without discectomy is a safe and effective procedure in the treatment of recurrent or residual cervical radiculopathy following prior anterior cervical discectomy and fusion. (2017ESJ138)

Influences of different fuel kinds and engine design parameters on the performance characteristics and NO formation of a spark ignition (SI) engine

This study reports the effects of different fuel kinds such as petroleum based liquid fuels (gasoline, benzene, hexane, iso-octane and toluene), petroleum based gaseous fuels (propane, methane and hydrogen) and alcohols (ethanol and methanol) and engine design parameters such as cylinder dimension, intake pressure and temperature, cylinder wall temperature, residual gas fraction, burning duration, spark timing, equivalence ratio and compression ratio on the engine performance and NO formation of a spark ignition (SI) engine fueled with various fuels. A verified combustion model with experimental studies has been used to understand the influences of engine design parameters and different fuel types on the engine performance and NO formation. The results showed that the engine design parameters and fuel type considerably affect the brake power (BP), brake thermal efficiency (BTE) and NO formation.

The Influence of GI and GII on the compression after impact strength of carbon fiber/epoxy laminates

This study measured the compression after impact strength of IM7 carbon fiber laminates made from epoxy resins with various mode I and mode II toughness values to observe the effects of these toughness values on the resistance to damage formation and subsequent residual compression strength-carrying capabilities. A total of seven different epoxy resin systems were used ranging in approximate GI values of 245–665 J/m2 and approximate GII values of 840–2275 J/m2. The results for resistance to impact damage formation showed that there was a direct correlation between GII and the planar size of damage as measured by thermography. Subsequent residual compression strength testing suggested that GI had no influence on the measured values and most of the difference in compression strength was directly related to the size of damage. Thus, delamination growth assumed as an opening type of failure mechanism does not appear to be responsible for the loss of compression strength.

Raman scattering in the submicrometer diamond membrane formed by the lift-off technique

Spectral characteristics of spontaneous Raman scattering in the submicrometer diamond membrane grown by the hydrogen implantation method are studied in comparison with the single-crystal diamond matrix. A shift in the main line of diamond one-photon excitation (sp 3-hybridization) at a frequency of 1324 cm−1 is revealed in the diamond membrane. This fact indicates multiple internal strains (residual compression strains) due to residual defects and is a concequence of the use of the hydrogen implantation method (hydrogen is implanted into diamond to form a sacrificial layer.

Increased stress and strain on the spinal cord due to ossification of the posterior longitudinal ligament in the cervical spine under flexion after laminectomy.

Myelopathy in the cervical spine due to cervical ossification of the posterior longitudinal ligament could be induced by static compression and/or dynamic factors. It has been suggested that dynamic factors need to be considered when planning and performing the decompression surgery on patients with the ossification of the posterior longitudinal ligament. A finite element model of the C2-C7 cervical spine in the neutral position was developed and used to generate flexion and extension of the cervical spine. The segmental ossification of the posterior longitudinal ligament on the C5 was assumed, and laminectomy was performed on C4-C6 according to a conventional surgical technique. For various occupying ratios of the ossified ligament between 20% and 60%, von-Mises stresses, maximum principal strains in the spinal cord, and cross-sectional area of the cord were investigated in the pre-operative and laminectomy models under flexion, neutral position, and extension. The results were consistent with previous experimental and computational studies in terms of stress, strain, and cross-sectional area. Flexion leads to higher stresses and strains in the cord than the neutral position and extension, even after decompression surgery. These higher stresses and strains might be generated by residual compression occurring at the segment with the ossification of the posterior longitudinal ligament. This study provides fundamental information under different neck positions regarding biomechanical characteristics of the spinal cord in cervical ossification of the posterior longitudinal ligament.

An assessment of axial pre-compression for the KSTAR central solenoid

The central solenoid (CS) of the KSTAR consists of four pairs of superconducting coils compressed axially by preloading structures. The axial pre-compression is needed to suppress the maximum attractive or repulsive force of the coils based on reference operation scenarios. All CS coils were assembled with eight sets of preloading and supporting structures under precise dimensional control. Only shells of preloading structures were heated to make 6mm gap between the preloading structure and coil assembly. The gap was, then, filled up by wedge movement so that axial pre-compression be applied after thermal contraction of shells. However measured pre-compression is about 55% of the design value. A detailed investigation has been carried out to find reasons for the preloading reduction by comparing strain measurement and structural analysis results. The minimum residual compression is estimated as 6.5MN. It is expected to have no serious problem during large plasma current H-mode discharge with consideration of the anti-slip design. A structural analysis model of KSTAR CS magnet has been developed based on the measured strains during operations and will give a guide line for future high performance and long pulse operations of KSTAR.

Design optimization of CFRP stacking sequence using a multi-island genetic algorithms under low-velocity impact loads

A method to improve the low-velocity impact performance of composite laminate is proposed, and a multi-island genetic algorithm is used for the optimization of composite laminate stacking sequence under low-velocity impact loads based on a 2D dynamic impact finite element analysis. Low-velocity impact tests and compression-after impact (CAI) tests have been conducted to verify the effectiveness of optimization method. Experimental results show that the impact damage areas of the optimized laminate have been reduced by 42.1% compared to the baseline specimen, and the residual compression strength has been increased by 10.79%, from baseline specimen 156.97 MPa to optimized 173.91 MPa. The tests result shows that optimization method can effectively enhance the impact performances of the laminate.

Identification of residual stress layers at glass surfaces via crack terminating angles

AbstractCracks terminating at free surfaces are affected by local stresses in the surface region. Under residual compression the crack front must retard compared with the crack contour in the absence of stresses. This effect can be used for an identification of residual stresses at glass surfaces. For an illustration of the procedure, Vickers indentation tests in soda‐lime glass are considered. Specimens treated by ion exchange and chemically toughening showed reduced terminating angles compared with untreated glass.

Risk Factors for Ineffectiveness of Posterior Decompression and Dekyphotic Corrective Fusion with Instrumentation for Beak-Type Thoracic Ossification of the Posterior Longitudinal Ligament: A Single Institute Study.

Thoracic ossification of the posterior longitudinal ligament (T-OPLL) is treated surgically with instrumented posterior decompression and fusion. However, the factors determining the outcome of this approach and the efficacy of additional resection of T-OPLL are unknown. To identify these factors in a prospective study at a single institution. The subjects were 70 consecutive patients with beak-type T-OPLL who underwent posterior decompression and dekyphotic fusion and had an average of 4.8 years of follow-up (minimum of 2 years). Of these patients, 4 (6%; group R) had no improvement or aggravation, were not ambulatory for 3 weeks postoperatively, and required additional T-OPLL resection; while 66 (group N) required no further T-OPLL resection. Clinical records, gait status, intraoperative ultrasonography, intraoperative neurophysiological monitoring (IONM), plain radiography, computed tomography and magnetic resonance imaging findings, and Japanese Orthopaedic Association (JOA) score were compared between the groups. Preoperatively, patients in group R had significantly higher rates of severe motor paralysis, nonambulatory status, positive prone and supine position test, no spinal cord floating in intraoperative ultrasonography, and deterioration of IONM at the end of surgery ( P < .05). In preoperative radiography, the OPLL spinal cord kyphotic angle difference in fused area, OPLL length, and OPLL canal stenosis were significantly higher in group R ( P < .05). At final follow-up, JOA scores improved similarly in both groups. Preoperative severe motor paralysis, nonambulatory status, positive prone and supine position test, radiographic spinal cord compression due to beak-type T-OPLL, and intraoperative residual spinal cord compression and deterioration of IONM were associated with ineffectiveness of posterior decompression and fusion with instrumentation. Our 2-stage strategy may be appropriate for beak-type T-OPLL surgery.

Traitements chirurgicaux de la névralgie trigéminale classique

Neurosurgical management of classical trigeminal neuralgia is based on three types of techniques: an “etiological” and nondestructive technique, microvascular decompression (MVD), which consists in decompressing the trigeminal nerve in the cerebello-pontine angle, where a vascular compression is frequently found at the origin of pain; percutaneous lesioning techniques (thermorhizotomy, microcompression by balloon, injection of glycerol), aimed at disrupting the transmission of the nociceptive message; and radiosurgery. During the consultation, the neurosurgeon will try to answer three questions: “Is this a trigeminal neuralgia?”; “Is it a classical form?”; and “Is it resistant to medical treatment?”. He will present to the patient the different surgical possibilities, emphasizing the “benefit/risk” balance, and propose the most adapted to his case. In a patient in good general condition, with a clear vascular compression at magnetic resonance imaging (MRI), it seems logical to discuss the first-line MVD, as this reference technique addresses the cause of classical trigeminal neuralgia and has a high probability level of good evolution on the long term. Radiosurgery can also be offered as an alternative because of its less invasiveness and morbidity (in particular, a very low rate of hypoesthesia compared to percutaneous techniques). A patient with an altered general condition or recurrence after MVD (without MRI residual vascular compression) may be referred for surgery or radiosurgery. Depending on the technique chosen, the patient should be informed that pain relief will often be “at the cost” of a hypoesthesia more or less pronounced. Between these two extreme and relatively easy cases, all intermediate situations are possible. In the absence of a randomized controlled study evaluating the different surgical techniques, the American Academy of Neurology and the European Federation of Neurological Societies admit that formal recommendations on surgical treatment cannot be made. However, these Scientific Societies indicate that (1) patients with an MVD have a longer pain-free period than other surgical techniques, at the cost of significant morbidity, reduced in teams with high activity in neuralgia and (2) radiosurgery is the technique with the least complication.

Comparison of 3 Methods for Maintaining Inter-Fragmentary Compression After Fracture Reduction and Fixation.

It is recommended that the intra-articular component of a supracondylar distal femoral fracture be stabilized by a lag screw to create interfragmental compression. Generally, it is thought that lag screw fixation should precede any positional screw or locking screw application. This study compared 3 methods of maintaining interfragmentary compression after fracture reduction with a reduction clamp. Intra-articular vertical split fractures were created in synthetic femora. A force transducer was interposed between the medial and lateral condyles and 20 lbs of compression was applied to the fracture with a reduction clamp. 3.5-mm cortical lag screws (group 1), 3.5-mm cortical position screws (group 2), and 5.4-mm distal locking screws through a distal femur locking plate (group 3) were placed across the fracture (n = 4/group). After screw placement, the clamp was removed and the amount of residual interfragmentary compression was recorded. After 2 minutes, a final steady-state force was measured and compared across groups. Locking screws placed through the plate (group 3) maintained 27% of the initial force applied by the clamp (P = 0.043), whereas positional screws (group 2) maintained 90% of the initial force applied by the clamp (P = 0.431). The steady-state compression force measured with lag screws (group 1) increased by 240% (P = 0.030) relative to the initial clamp force. The steady-state force in the lag screw group was significantly greater than groups 1 and 2 (P = 0.012). When reducing intra-articular fractures and applying interfragmentary compression with reduction clamps, additional lag screws increase the amount of compression across the fracture interface. Compressing a fracture with reduction clamps and relying on locking screws to maintain the compression result in a loss of interfragmentary compression and should be avoided. This study lends biomechanical support that lag screws placed outside of the plate before locking screws for fracture fixation help maintain optimal interfragmentary compression.