Klasik laminasyon teorisinin üç boyutlu yazıcı ile eriyik yığma modelleme yöntemi kullanılarak üretilmiş plastiklere uygulanması ve tam alanlı yüzey gerinim haritalanması

In this study, five differently oriented sets of 3D-printed tensile samples are produced using the Fused Deposition Method (FDM). Among these five sets, three are used to determine the elastic constant to be used in Classical Lamination Theory (CLT), which is generally used to model fiber-reinforced polymers (FRP). Based on the obtained results, CLT is further applied to the remaining two sets of unreinforced 3D-printed polymer samples where the deposition direction varies in each layer. The stress and strain calculated with CLT are then compared with experimental results obtained through tensile testing. The comparison depicts that experimental and CLT results are in good agreement at lower strain levels. In contrast, the stress calculated with CLT deviates from the experimental result at the higher strain levels. Thereafter, a full-field surface strain mapping is applied by using Digital Image Correlation (DIC) Techniques to reveal the damage progression and failure of Fused Deposition Method 3-D Printed PlasticsBu çalışmada üç boyutlu yazıcı ile Eriyik Yığma Modellemesi (EYM) yöntemi kullanılarak farklı yazma yönlerindeki katmanlara sahip toplamda beş set çekme örneği üretilmiştir. Üretilen üç farklı sete çekme testi yapılarak farklı yönlerdeki elastik sabitler daha sonra Klasik Laminasyon Teorisinde (KLT) kullanılmak üzere ölçülmüştür. Klasik Laminasyon Teorisi genel olarak tek yönlü fiberler ihtiva eden polimerik yapıların modellenmesi için kullanılmaktadır. Bu çalışma ile KLT üç boyutlu yazıcı ile üretilen ve içerisinde herhangi bir fiber takviyesi ihtiva etmeyen ve her katmanda yazma yönleri değişen iki farklı polimerik yapıya uygulanmıştır. KLT ile elde edilen gerinim ve gerilme değerleri çekme deneyi ile elde edilen gerinim ve gerilme değerleri ile karşılaştırmıştır. Elde edilen sonuçlara göre düşük gerinim değerleri için KLT ile elde edilen sonuçların deneysel sonuçlar ile uyumlu olduğu, yalnız gerinim değeri arttıkça KLT ile hesaplanan değerlerinin deneysel değerlerden uzaklaştığı görülmüştür. Daha sonra ise Eriyik Yığma Modelleme Yöntemi ile üretilen üç boyutlu plastiklerin hasar ilerlemesi ve kırılması Dijital Görüntü Korelasyon Tekniği ile Tam Alanlı Yüzey Gerinim Haritalanması kullanılarak çıkarılmıştır

Manufacturing of microcapsules with liquid core and their self-healing performance in epoxy for resin transfer molding

Microcapsules with different active core materials have been receiving a great deal of attention for developing polymer based materials with selfhealing abilities. The self-healing ability is crucial in particular for matrix materials having brittle nature such as epoxy resin. In order for abstaining from an abrupt failure of structural brittle manner polymeric materials, microcapsules can be used excellently as a viable repair agent. In this work, we present a study on the catalyst-free microcapsule based self-healing system. Microcapsules were produced by the insitu polymerization of urea-formaldehyde at the dispersed phase-water interface. Each microcapsule batches were characterized by using Fourier Transform Infrared Spectroscopy (FTIR), Thermogravimetric Analyser (TGA), Di erential Scanning Calorimetry (DSC). Characteristic peaks of urea-formaldehyde shell, core components; DGEBA, and PhCl was seen in the Mid- IR region. Characteristic thermal decomposition temperature of urea-formaldehyde wall material and DBEBA which is the main microcapsule content were determined from the TGA trace. In addition to the given thermal and spectral characterization tools, optic microscope and SEM images also ensure the formation of liquid- lled microcapsules. Although the microcapsules showed brittle behavior during the processing such as drying and sieving, incorporation of microcapsules into the epoxy matrix was achieved successfully. The healing characteristic of epoxy-microcapsule composite was assessed by the Tapered Double Cantilever Beam (TDCB) specimen at the mode-I crack opening fashion. Besides microcapsule-epoxy composite system showed a moderate healing efficiency, a significant increase in mode-I fracture toughness value was observed. Three point bending experiment was also conducted on the microcapsule-epoxy composite. It was found that microcapsules drastically decrease the flexure strength of questioned host material

Monitoring the damage state of fiber reinforced composites using an FBG network for failure prediction

A structural health monitoring (SHM) study of biaxial glass fibre-reinforced epoxy matrix composites under a constant, high strain uniaxial fatigue loading is performed using fibre Bragg grating (FBG) optical sensors embedded in composites at various locations to monitor the evolution of local strains, thereby understanding the damage mechanisms. Concurrently, the temperature changes of the samples during the fatigue test have also been monitored at the same locations. Close to fracture, significant variations in local temperatures and strains are observed, and it is shown that the variations in temperature and strain can be used to predict imminent fracture. It is noted that the latter information cannot be obtained using external strain gages, which underlines the importance of the tracking of local strains internally

Neurobrucellosis with transient ischemic attack, vasculopathic changes, intracerebral granulomas and basal ganglia infarction: a case report

<p>Abstract</p> <p>Introduction</p> <p>Central nervous system involvement is a rare but serious manifestation of brucellosis. We present an unusual case of neurobrucellosis with transient ischemic attack, intracerebral vasculopathy granulomas, seizures, and paralysis of sixth and seventh cranial nerves.</p> <p>Case presentation</p> <p>A 17-year-old Caucasian man presented with nausea and vomiting, headache, double vision and he gave a history of weakness in the left arm, speech disturbance and imbalance. Physical examination revealed fever, doubtful neck stiffness and left abducens nerve paralysis. An analysis of his cerebrospinal fluid showed a pleocytosis (lymphocytes, 90%), high protein and low glucose levels. He developed generalized tonic-clonic seizures, facial paralysis and left hemiparesis. Cranial magnetic resonance imaging demonstrated intracerebral vasculitis, basal ganglia infarction and granulomas, mimicking the central nervous system involvement of tuberculosis. On the 31st day of his admission, neurobrucellosis was diagnosed with immunoglobulin M and immunoglobulin G positivity by standard tube agglutination test and enzyme-linked immunosorbent assay in both serum and cerebrospinal fluid samples (the tests had been negative until that day). He was treated successfully with trimethoprim and sulfamethoxazole, doxycyline and rifampicin for six months.</p> <p>Conclusions</p> <p>Our patient illustrates the importance of suspecting brucellosis as a cause of meningoencephalitis, even if cultures and serological tests are negative at the beginning of the disease. As a result, in patients who have a history of residence or travel to endemic areas, neurobrucellosis should be considered in the differential diagnosis of any neurologic symptoms. If initial tests fail, repetition of these tests at appropriate intervals along with complementary investigations are indicated.</p

An experimental study on tensile and bending properties of biaxial warp knitted textile composites

This study presents the results of an experimental research on scrutinizing the tensile and flexural attributes of biaxial warp knitted (BWK) composites with different fabric weight content controlled by the density of the warp and weft fibres. Resin Transfer Molding (RTM) method has been used to produce composite laminates with two different fabric weights (813 and 1187 gr/m2) and with three different stacking sequences [90we/0wa/90we/0wa]s, [90wa/0we/90wa/0we]s and [90wa/0we/90we/0wa]s, leading to six different types of composite panels, which are processed into a number of specimens for tensile and flexural tests. The fracture surfaces of the mechanically tested specimens have been examined microscopically. The results indicate that composites with lower weft and warp fibre thicknesses (thin-ply) show higher tensile and bending properties compared to those with higher weft and warp fibre thicknesses (thick-ply)

Effect of fiber densities on impact properties of biaxial warp-knitted textile composites

In this study, an appropriate fabric weight content controlled by the density of the warp and weft fibers is determined for biaxial warp-knitted composites referring to mechanical test results. Six different types of composite panel with two different fabric weights (813 and 1187 gr/m(2)) and with three different stacking sequences [90(we)/0(wa)/90(we)/0(wa)](s), [90(wa)/ 0(we)/90(wa)/0(we)](s), and [90(wa)/0(we)/90(we)/0(wa)](s) are fabricated by using Resin Transfer Molding method. Having produced composite panels, drop weight impact tests are conducted on specimens. Microstructural characterization of impact tested materials is performed using optical microscope. The results of this study reveal that composites with biaxial warp-knitted preforms with lower weft and warp fiber densities (thin-ply) could absorb higher impact energies compared to those with higher weft and warp fiber densities (thick-ply)

Non-destructive determination of the stiffness matrix of a laminated composite structure with lamb wave

This study presents a combined experimental and numerical study on the determination of the stiffness matrix of transversely isotropic thin laminated composite structures non-destructively with the use of group velocity measurements. The approach relies on the usage of A0 and S0 modes of Lamb waves, triggered the by pencil-lead break, which propagate in the composite material, and enables the evaluation of various elements of the stiffness matrix. It is proven that the experimental Lamb wave method can be reliably utilized for determining the components of the stiffness matrix, C-ij. The results are validated with respect to those of mechanical characterization and finite element analysis