Residual Strain Values Research Articles

Residual Strain in PCBs with Cu-Plated Holes

The residual strain in pure printed circuit boards (PCBs) and PCBs with Cu-plated holes has been obtained by measurement of the temperature dependence of their dilatational characteristics in the x, y, and z directions up to 240°C. Shrinkage in all directions was observed for all samples of both materials in the first thermal cycle. No permanent length changes were observed in the second or subsequent thermal cycles. The residual strain was determined from the difference in relative elongation between the first and second thermal cycles. Relaxation of residual strain occurred only in the first thermal cycle, as a thermally activated process. The highest value of relaxed residual strain was found in the z direction for both materials. Relaxation of residual strain in the z direction of the pure PCB occurred only in the negative strain range, whereas relaxation of the PCB with Cu-plated holes occurred in both the positive and negative strain ranges. The relaxation of the positive strain in the PCB with Cu-plated holes in the z direction implies that this part of the PCB was under pressure during its preparation. This relaxation is a consequence of the high coefficient of thermal expansion of PCB laminate in this direction, which can also lead to cracks in Cu holes when the material is heated above the glass-transition temperature.

Rapid Recovery Double Cross-Linking Hydrogel with Stable Mechanical Properties and High Resilience Triggered by Visible Light.

The designed tough hydrogels, depending on energy dissipation mechanism, possess excellent biocompatibility, stimuli-responsiveness, and outstanding mechanical properties. However, the application of hydrogels is greatly limited in actuators and sensors for the lack of instantaneous recovery and resilience. In this work, we synthesized a double cross-linking poly(acrylic acid) hydrogel via a simple, one-pot, visible-light-trigger polymerization, with carboxymethyl cellulose as initiator and the first cross-linker, N,N'-methylene bis(acrylamide) (MBA) as the second cross-linker. The tensile strength and elastic modulus are in the range of 724-352 kPa and 115-307 kPa, respectively, depending on the MBA content. The swelling ratio of hydrogels dramatically decreased with increasing the MBA content. DMA results indicate that the internal friction between molecules within the hydrogel decreases with the increase of MBA content. Cyclic tensile tests show that after the structure stabilizes, the resilience, maximum stress, and residual strain of Gel-2 maintains over 93% (95% for successive cyclic tensile test), 115 kPa and less than 3%, respectively, at a strain of 125%. The values of resilience and residual strain are almost constant in both successive and intermittent cyclic tensile tests. Moreover, the swollen hydrogel has higher resilience and lower residual strain than the same hydrogel in the as-prepared state.

Welding distortion and inherent deformation under temporary tacking and its released states

In the present study, the detailed welding distortion of bead welded plates under temporary tacking state and released state was predicted by thermal elastic-plastic finite element model (FEM) and also measured by the digital image correlation (DIC) method. It was found that the residual welding angular distortion can be reduced to about 50–60% by temporary tacking, while the residual transverse shrinkage and longitudinal shrinkage are less affected. Further, the welding distortion with different ratios of temporary tacking length to weld length for various dimensions of bead welded plates was quantitatively investigated by FEM. The inherent deformations which are described by the integrated values of residual plastic strains were proved to be the same before and after releasing the temporary tacking. The effect of temporary tacking on the welding distortion and inherent deformation were analysed in details.

High-energy synchrotron X-ray diffraction measurements of simple bending of pseudoelastic NiTi shape memory alloy wires

Many technological applications of austenitic shape memory alloys (SMAs) involve cyclical mechanical loading and unloading in order to take advantage of pseudoelasticity. In this paper, we investigated the effect of mechanical bending of pseudoelastic NiTi SMA wires using high-energy synchrotron radiation X-ray diffraction (SR-XRD). Differential scanning calorimetry was performed to identify the phase transformation temperatures. Scanning electron microscopy images show that micro-cracks in compressive regions of the wire propagate with increasing bend angle, while tensile regions tend not to exhibit crack propagation. SR-XRD patterns were analyzed to study the phase transformation and investigate micromechanical properties. By observing the various diffraction peaks such as the austenite (200) and the martensite (${\bar 1}12$), (${\bar 1}03$), (${\bar 1}11$), and (101) planes, intensities and residual strain values exhibit strong anisotropy, depending upon whether the sample is in compression or tension during bending.

In-situ monitoring of strain and temperature distributions during fused deposition modeling process

The present work investigates the integration of fiber Bragg grating (FBG) sensors for continuous in-situ and in real-time monitoring of strain fields build up as well as of developed temperature profiles during the fabrication procedure of structures built via the Fused Deposition Modeling (FDM) technology. A methodology is presented for simultaneous monitoring of strain and temperature profiles from the recorded spectrum of an embedded optical sensor when the deposited material remains close to its glass transition temperature. The used FBG sensors were embedded either longitudinally or transversely to the test samples' long axis and within different layers of the structures. Analysis of the FBG recordings indicates that the generated residual strain values are significant during material consolidation of the deposited layers. It is also shown that the solidification induced strain levels and the developed temperature gradients are strongly influenced by the samples' position onto the building platform. The findings demonstrate that an embedded optical sensing system is proven to be a reliable choice for real-time monitoring of the FDM process and the printed part's quality.

Post-Cyclic Behavior of Carbonate Sand of the Northern Coast of the Persian Gulf

The post-cyclic behavior of biogenic carbonate sand was evaluated using cyclic triaxial testing through a stress control method under different confining pressures between 50 to 600 kPa. The testing program included a series of isotropically and anisotropically consolidated, undrained triaxial compression and extension tests on samples of remolded calcareous Bushehr sand. Grading analyses (before and after each test) were used to examine the influence of particle breakage on post-cyclic behavior of Bushehr sand. The particle breakage commonly occurred in these soils even in lower values of confining pressure, yet there was not a clear correlation between the post-cyclic responses and particle breakage. Based on the present study, a concept is suggested for post-cyclic behavior of carbonate sand. It was observed that post-cyclic strength has a good correlation with cyclic stress ratio, type of consolidation, and value of residual cyclic strain. For all specimens, it is clear that the post-cyclic strength is greater than monotonic strength, irrespective of confining pressure and relative density.

Applied, residual strain and texture investigations by means of neutron time-of-flight diffraction combined with acoustic emission detection: Application to a gneiss sample from Forsmark, Sweden

The mechanical behaviour of a gneiss sample from the Forsmark drilling site (Sweden) consisting of quartz, plagioclase (oligoclase), microcline and biotite, is characterized by residual strain and crystallographic preferred orientation measurements. Cyclic in situ uniaxial deformation experiments were carried out on a cylindrical sample at four uniaxial stress levels (55, 84, 114 and 141 MPa) and examined using time-of-flight neutrons and simultaneous recording of acoustic emissions. At each stress level applied, a residual strain scan was performed around the sample axis and residual strains were determined. The residual compressional strain detected for quartz was −1.0 × 10−3, the maximum value of residual strain approached 1.2 × 10−3. The onset of acoustic emissions is an indicator of the previous in situ maximum stress. Comparison of acoustic emission data with applied and residual stress values at different load levels is the key to understand the freezing-in mechanism of residual stress and the Kaiser Effect in rock.

Deformation properties of sedimentary rocks in the process of underground coal gasification

Abstract The article presents results of research into changes in deformation properties of rocks, under influence of temperature, during the process of underground coal gasification. Samples of carboniferous sedimentary rocks (claystones and sandstones), collected in different areas of Upper Silesian Coal Basin (GZW), were heated at the temperature of between 100 and 1000–1200 °C, and then subjected to uniaxial compression tests to obtain a full stress-strain curves of the samples and determine values of residual strain and Poisson's ratio. To compare the obtained values of deformation parameters of rocks, tested in dry-air state and after heating in a given range of temperature, normalised values of residual strain and Poisson's ratio were determined. Based on them, coefficient of influence of temperature on tested deformation parameters was determined. The obtained values of the coefficient can be applied in mining practice to forecast deformability of gangue during underground coal gasification, when in the direct surrounding of a georeactor there are claystones or sandstones. The obtained results were analysed based on classification of uniaxial compression strength of GZW gangue, which formed the basis for dividing claystones and sandstones into very low, low, medium and high uniaxial compression strength rocks. Based on the conducted tests it was concluded that the influence of uniaxial compression strength on the value of residual strain, unlike the influence of grain size of sandstones, is unambiguous within the range of changes in the parameter. Among claystones changes in the value of Poisson's ratio depending on their initial strength were observed. Sandstones of different grain size either increased or decreased the value of Poisson's ratio in comparison with the value determined at room temperature in dry-air conditions.

Effect of Crêpe Texture on Tensile Properties of Cotton Fabric under Varied Relative Humidity

The physical properties of cotton crepe fabrics with highly twisted weft yarn (2200 twists per meter) were evaluated after special embossed finishing to generate pique. The effect of pique was investigated as the main factor affecting the tensile properties of the sample fabrics under varied relative humidity. First, the mechanical and surface properties were measured using the Kawabata Evaluation System for Fabrics under standard room conditions, and then, the other physical properties were examined. The existence of pique in the crepe texture significantly changed the samples’ tensile properties, such as tensile energy and extensibility at maximum applied load (EM) in the weft direction. Additional tensile measurements were carried out under varied relative humidity (10-90% RH) at 25°C. The crepe fabrics with pique had higher EM and residual strain values than the non-pique samples under all RH conditions. In particular, the effect of pique on EM became obvious at 90% RH.

Endotaxially stabilized B2-FeSi nanodots in Si (100) via ion beam co-sputtering

We report on the formation of embedded B2-FeSi nanodots in [100]-oriented Si substrates, and investigate the crystallographic mechanism underlying the stabilization of this uncommon, bulk-unstable, phase. The nanodots were approximately 10 nm in size, and were formed by iron thin film deposition and subsequent annealing. Cross-sectional transmission electron microscopy, energy loss spectroscopy mapping, and quantitative image simulation and analysis were utilized to identify the phase, strain, and orientational relationship of the nanodots to the host silicon lattice. X-ray photoelectron spectroscopy was utilized to analyze the surface composition and local bonding. Elasticity calculations yielded a nanodot residual strain value of −18%. Geometrical phase analysis graphically pinpointed the positions of misfit dislocations, and clearly showed the presence of pinned (11¯1¯)Si//(100)FeSi, and unpinned (2¯42)Si//(010)FeSi, interfaces. This partial endotaxy in the host silicon lattice was the mechanism that stabilized the B2-FeSi phase.

Strain and Texture Investigations by Means of Neutron Time-of-Flight Diffraction: Application to Polyphase Gneisses

Two polyphase gneiss samples (Western Alps, Switzerland) consisting of quartz, albite, muscovite and microcline have been investigated with respect to anisotropic physical properties - residual and applied strain - and crystallographic preferred orientations. The samples were taken in close vicinity to a fault structure. For texture evaluation the 'Rietveld texture analysis' has been applied, because reliable texture analysis of polyphase rocks from pole figures is problematic due to multiple peak overlaps. The quartz textures of both samples are strong and rather similar, whereas albite and microcline show a nearly random distribution. In contrast, the mica texture is pronounced and complex. The basal plane normals of muscovite are preferably oriented parallel to [-direction of the structural reference frame and switch to [-direction with residual orientations in [ and a transition into the [-[-plane within the fault. This might be the result of quartz recrystallization, if mica is used as reference according the applied stress field. A residual strain scan has been carried out along the axis of a cylindrical sample (d = 30 mm, l = 60 mm). Residual strain values of quartz have been detected with a minimum of-1.6×10-3, and maximum strain values of 1.2×10-3. Uniaxial compression experiments in discrete steps up to 53 MPa were performed, for each step the applied and residual strains were determined. The strain increases up to 28 MPa; surprisingly, lower strain values are detected at higher applied stresses.

Strain evolution during the growth of epitaxial Ge layers between narrow oxide trenches

We have grown the high quality and compressively strained Ge epilayers on a Si substrate with 40-nm width SiO2 trench patterns at a growth temperature of 600°C. Based on (224) reciprocal space mapping measurements of Ge samples with a different thickness, the residual in-plane strain value along the trench direction decreased from −0.74% to −0.42% with increasing thickness of the Ge layer from 150 nm to 180 nm. In addition, the compressive strain along the trench direction (ε1¯10) was larger than that in the direction perpendicular to the trench (ε110) regardless of the thickness. For example, when Ge was overgrown on a SiO2 trench, the ε1¯10 and ε110 values were −0.42% and ~0%, respectively. We conclude that the asymmetric strain relaxation behavior of Ge is related to the SiO2 trench patterns, which prevent the dislocations from gliding. Defects such as a microtwin and/or stacking fault were generated during the coalescence of Ge films having different lattice constants in each Ge layer arising from the different relaxation values. A local strain in Ge, with a high spatial resolution of 2.5nm, was measured along the two directions by means of a nanobeam electron diffraction method, thus confirming asymmetric strain relaxation and the results are in good agreement with reciprocal space mapping results.

Morpho-mechanical intestinal remodeling in type 2 diabetic GK rats—Is it related to advanced glycation end product formation?

Little is known about the mechanisms for the biomechanical remodeling in diabetes. The histomorphology, passive biomechanical properties and expression of advanced glycation end product (N epsilon-(carboxymethyl) lysine, AGE) and its receptor (RAGE) were studied in jejunal segments from 8 GK diabetic rats (GK group) and 10 age-matched normal rats (Normal group). The mechanical test was done by using a ramp distension of fluid into the jejunal segments in vitro. Circumferential stress and strain were computed from the length, diameter and pressure data and from the zero-stress state geometry. AGE and RAGE were detected by immunohistochemistry staining. Linear regression analysis was done to study association between the glucose level and AGE/RAGE expression with the histomorphometric and biomechanical parameters. The blood glucose level, the jejunal weight per length, wall thickness, wall area and layer thickness significantly increased in the GK group compared with the Normal group (P<0.05, P<0.01 and P<0.001). The opening angle and absolute values of residual strain decreased whereas the circumferential stiffness of the jejunal wall increased in the GK group (P<0.05 and P<0.01). Furthermore, stronger AGE expression in the villi and crypt and RAGE expression in the villi were found in the GK group (P<0.05 and P<0.01). Most histomorphometric and biomechanical changes were associated with blood glucose level and AGE/RAGE expression. In conclusion, histomorphometric and biomechanical remodeling occurred in type 2 diabetic GK rats. The increasing blood glucose level and the increased AGE/RAGE expression were associated with the remodeling, indicating a causal relationship.

Origin of tensile strain in GaN grown on AlGaN/AlN stress mitigating layers on 100-mm Si (1 1 1) by ammonia molecular beam epitaxy

AbstractThe origin of tensile strain in GaN grown on AlGaN/AlN stress mitigating layers on 100-mm Si (111) was investigated by varying the AlGaN growth temperature. GaN grown on higher AlGaN growth temperature exhibited two dimensional growth mode while three dimensional growth mode was obtained for GaN grown on lower AlGaN growth temperature. Micro-Raman and high-resolution X-ray diffraction techniques were employed to measure the residual tensile strain in GaN. The average plastic relaxation was calculated to obtain the tensile strain in GaN due to dislocation looping. The measured and calculated residual tensile strain values were compared to determine the origin of tensile strain. The average plastic relaxation and the tensile strain generated due to the grain coalescence were found to be the major factors influencing the strain states of GaN grown on AlGaN/AlN stress mitigating layers, in addition to the tensile strain generated due to the thermal mismatch.

Effect of chang run tong on the biomechanical and morphometric remodeling of colon and rectum in streptozotocin-induced diabetic rats

The present study investigates the effect of Chang Run Tong (CRT) on the biomechanical and morphometrical remodeling of colon and rectum in streptozotocin-induced diabetic rats. The colonic and rectal segments were obtained from diabetic (DM), CRT-treated diabetic (T1, high dosage: 50 g/kg/day; T2, low dosage: 25 g/kg/day) and normal (Con) rats. The experimental period was 60 d. The blood glucose level and body weight were measured. The circumferential length, wall thickness, and opening angle were measured from the segments in the no-load and zero-stress states. The residual strain was computed from the morphometry data. The step-wise distension was done on the colonic segment (from 0 to 20 cmH2O). The circumferential and longitudinal stresses and strains were computed. The blood glucose level was significantly higher and the body weight was significantly lower in the DM, T1, and T2 groups compared to those in the Con group (p ＜ 0.01, p ＜ 0.001). The glucose level did not differ among the DM, T1, and T2 groups. The wet weight per unit length to body weight ratio, wall thickness, cross-sectional wall area, opening angle, and absolute value of residual strain of colonic and rectal segments in the DM group were significantly higher than those in the Con group (p ＜ 0.05 and p ＜ 0.01), and those in the T1 group, but not those in the T2 group, were significantly lower than those in the DM group (p ＜ 0.05, p ＜ 0.01). Furthermore, the circumferential and longitudinal stiffness of the colonic wall in the DM group was higher than those in the Con group. T1, but not T2, treatment could significantly decrease the colonic wall stiffness in both directions (p ＜ 0.01). CRT (high dose) treatment could partly restore the morphometric and biomechanical remodeling of the lower gastrointestinal tract in diabetic rats.

Characterization of reduced pressure chemical vapor deposited Si0.8Ge0.2/Si multi-layers

We have investigated the Si0.8Ge0.2/Si multi-layer grown directly onto the Si (001) substrates using reduced pressure chemical vapor deposition. The thicknesses of the Si0.8Ge0.2/Si multi-layer were determined using transmission electron microscopy. From the results of energy-dispersive X-ray spectroscopy and X-ray diffraction analyses on the Si0.8Ge0.2/Si multi-layer, Ge composition in the Si1−xGex layers was determined as ∼20% and the value of residual strain ε of the Si0.8Ge0.2 layer is calculated to be 0.012. Three peaks are observed in Raman spectrum, which are located at approximately 514, 404, and 303cm−1, corresponding to the vibration of Si–Si, Si–Ge, and Ge–Ge phonons, respectively. The photoluminescence spectrum originates from the radiative recombinations both from the Si substrate and the Si0.8Ge0.2/Si multi-layer. For the Si0.8Ge0.2/Si multi-layer, the transition peaks related to the quantum well region observed in the photocurrent spectrum were preliminarily assigned to e–hh and e–lh fundamental excitonic transitions.

Variation in the coercive force under static tension and fatigue loading of specimens of steel ShKh15

The behavior of the coercive force is analyzed for specimens of annealed steel ShKh15 under static tension and zero-to-tension cyclic loading over a wide range of stress amplitudes. The possibility has been found for rapid and reliable determination of the amplitude ranges under low-and high-cycle fatigue and also the quasistatic loading due to a high sensitivity of the coercive force to the residual plastic strain value of the steel.

Superelastic behaviour analysis of a shape memory coronary stent

Shape memory alloys have been attracting much attention with smart materials applications in various fields. Especially, it has found a wide use in medical and dental applications with discovery of Nitinol. In this study, the effects of displacement and change of temperature on the superelastic behaviour of a coronary stent were investigated using finite element method. Solid model of coronary stent generated by SolidWorks, was transferred to ANSYS finite element software which uses the Auricchio model to analyze the superelastic behaviour of shape memory alloys. The radial displacement had a negligible effect on hysteresis of shape memory coronary stent, whereas the stress–strain values of martensitic structure were affected. The stiffness and maximum residual strain values of the shape memory coronary stent were also significantly affected by temperature changes; thus, they increased with increasing temperature.

Elastic properties of polypropylene/ethylene–octene copolymer blends

Blends of polypropylene (PP) and ethylene–octene copolymer (EOC) across the whole composition range (10, 20, …, 80, 90 wt.%) were investigated with focus on mechanical properties. Samples (0–50% of PP) were stretched in a tensile machine to given elongations (100, 200 and 300%) and then the crosshead returned to the initial position. The residual strain values were obtained from the hysteresis curves. These residual strain values were plotted as a function of applied strain and PP content. Stress at given elongation (M100 and M300) was also plotted as a function of PP content. At low PP content (0–20%), residual strain and stress at given elongation are close to those of pure EOC. A steeper increase in these values was observed for concentrations 20–50% of PP. Another set of experiments involved tensile testing to break (full range of concentrations). From these experiments, tensile modulus and stress at break were evaluated and plotted as a function of PP content. Modulus values were close to that of pure EOC in the range of 0–25% of PP. Then, the values start to increase almost linearly with increasing PP content. The mechanical properties of the blends were correlated with the structure observed by transmission electron microscopy (TEM). At 20% PP, there are PP particles with round shape uniformly dispersed in the EOC matrix. When the PP content increased to 30%, the shape of the PP particles changed to elongated. In the case of 40% of PP, the structure resembles a co-continuous one. Differential scanning calorimetry (DSC) revealed the nature of the excellent elastic behavior of EOC. EOC crystals at 7 wt% act as tie points for amorphous chains (physical cross-linking).

Biomechanical remodelling of obstructed guinea pig jejunum

Data on morphological and biomechanical remodelling are needed to understand the mechanisms behind intestinal obstruction. The effect of partial obstruction on mechanical properties with reference to the zero-stress state and on the histomorphological properties of the guinea pig small intestine was determined in this study. Partial obstruction and sham operation were surgically created in mid-jejunum of guinea pigs. The animals survived 2, 4, 7, and 14 days. The age-matched guinea pigs that were not operated served as normal controls. The segment proximal to the obstruction site was used for histological analysis, no-load state and zero-stress state data, and distension test. The segment for distension was immersed in an organ bath and inflated to 10 cm H 2O. The outer diameter change during the inflation was monitored using a microscope with CCD camera. Circumferential stresses and strains were computed from the diameter, pressure and the zero-stress state data. The opening angle and absolute value of residual strain decreased ( P<0.01 and P<0.001) whereas the wall thickness, wall cross-sectional area, and the wall stiffness increased after 7 days obstruction ( P<0.05, P<0.01). Histologically, the muscle and submucosa layers, especially the circumferential muscle layer increased in thickness after obstruction. The opening angle and residual strain mainly depended on the thickness of the muscle layer whereas the wall stiffness mainly depended on the thickness of the submucosa layer. In conclusion, the histomorphological and biomechanical properties of small intestine (referenced for the first time to the zero-stress state) remodel proximal to the obstruction site in a time-dependent manner.