Loop Patches Research Articles

A Broadband High-Gain Printed Antenna Array Using Dipole and Loop Patches for 5G Communication Systems

A broadband and high-gain printed antenna array is presented in this paper. Its single antenna element consists of a loop and two symmetric dipole patches, making the element exhibiting broad impedance bandwidth and improved gain at the targeted frequency, which is 28 GHz, one of the 5G mm-wave band, for this design. An 8×3 antenna array fed by a microstrip line feed network was designed and simulated. With a compact size of 98×32.5 mm2 , the array presents a broad -10 dB impedance bandwidth of 6.8 GHz (24.3%) and a high gain of 18 dBi at 28 GHz. Besides, the single-layered array also features low profile, simple geometry, and low cost, making it a good candidate for 5G communication systems.

The effect of pH on antibody retention in multimodal cation exchange chromatographic systems

The present paper builds upon previous work on mAb domain contributions to multimodal (MM) chromatography by examining how pH can impact mAb surface properties and retention in these systems. Linear salt gradient experiments were carried out between pH 5–7 for several mAbs with different pI and surface hydrophobicities in four different MM CEX resins at two ligand densities. mAb retention showed an inverse, non-linear correlation with pH. Changing pH affected the elution order, creating unique windows of selectivity in each of the MM CEX resins. One mAb showed a pH-dependent spectrum of domain contributions, demonstrating that pH can be used to tune the relative importance of the (Fab)2 and Fc domains for some mAbs in MM systems. Positive, negative, and hydrophobic patches were calculated between pH 5–7 for the mAbs. Visualizing these patches on the protein surface demonstrated that each mAb showed a unique distribution of surface charge and hydrophobicity that changed with pH. The sum of patch areas was tracked across this pH range to quantitatively understand how pH impacted these important surface properties. The quantitative analysis then was narrowed to consider only patches in the CDR loops, which were hypothesized to be an important interaction site for some mAbs in these systems. Interestingly, differences in the titration of CDR loop patches for each mAb were shown to be a result of Histidine titrations and patches in this region were qualitatively correlated with experimental trends including the observed elution order reversals. These results indicate that pH potentially can be employed as a lever for the strategic design of multimodal steps to create flow through, bind and elute, or weak partitioning operations with important implications for the design of integrated and/or continuous downstream purification processes. Furthermore, the ability to tune domain contributions in MM separations using pH creates intriguing possibilities for current downstream challenges such as the removal of product-related impurities, as well as the purification of bispecific mAbs.

The effects of grain boundary on dislocation development for cyclically deformed IF steel

Polycrystalline interstitial-free steels (IF steels) were cyclically deformed at constant total strain amplitude (Δ ɛ/2) in the range from 0.05% to 0.6%. The transformed speed of loop patches into dislocation cells and walls near grain boundary is faster than that in the grain interior while total strain amplitude is lower than 0.15%. However, the well-known dislocation-free zones (DFZs) near grain boundary are very hard to be found in this study. Additionally, dislocation cells tend to transform into loop-patch structure near grain boundary during high–low strain-controlled fatigue test (two-step fatigue test).

Evolution of dislocations in large grains of polycrystalline copper under low cycle fatigue with reduced strain amplitude

This work examines the evolution of the dislocation structure in large grains of polycrystalline copper with decreasing strain amplitude. The experimental results show that (1) dislocation reversal is initially triggered by the operation of a final slip system, which is formed by the previously high strain amplitude when the strain amplitude is reduced; and (2) the region that is occupied by the dislocation reversal structures called loop patches. It is small in large grains because a more homogenous internal stress distribution induces a more uniform evolution of dislocations in large grains.

Dislocation evolution in interstitial-free steel during fatigue near the endurance limit

In order to clear the relationship between dislocation development and endurance limit in fatigued body-centered cubic (BCC) metals, the automotive grade interstitial-free steel (IF steel) was fatigued near the endurance limit in this study. When cycling just below the endurance limit, the dislocation structures are mainly composed of loop patches, moreover, a few large dislocation cells and dislocation walls can also be found, and thus these structures have no significant effect on fatigue failure. However, once cyclic strain slightly exceeds the endurance limit, the small dislocation cells tend to develop near grain boundaries and triple junction of the grains, and which provide a more appropriate structure for crack growth than do large dislocation cells.

Transmission and scanning electron microscope study on the secondary cyclic hardening behavior of interstitial-free steel

Strain controlled fatigue experiment was employed to evaluate automotive grade interstitial-free ferrite steel. Hundreds of grains were examined by scanning electron microscope under electron channeling contrast image technique of backscattered electron image mode for comprehensive comparison of micrographs with those taken under transmission electron microscope. The cyclic stress responses clearly revealed that rapid hardening occurs at the early stage of cycling as a result of multiplication of dislocations to develop loop patches, dipolar walls and dislocation cells at various total strain amplitudes. After primary rapid hardening, stress responses varied from being saturated to further hardening according to dislocation structure evolution at various strain amplitudes. The fatigue failure was always accompanied with further hardening including secondary hardening. The corresponding dislocation structures with the three types of hardening behaviors are discussed. Once the secondary hardening starts, dislocation cells began to develop along grain boundaries in the low strain region and then extended into grain interiors as strain amplitudes increased and cycling went on. The secondary hardening rates were found to be directly proportional to their strain amplitudes.

The relationship between cyclic stress–strain curve and dislocation structures in cyclically deformed IF steel

The cyclic stress–strain curve (CSSC) of cyclically deformed polycrystalline interstitial-free steels (IF steel), divided into regions A, B and C, have been correlated with the fatigue test conditions. No dislocation arrangement can be found when plastic strain amplitude is controlled in region A. For region B as revealed as a plateau, the plastic strain amplitude is located in the range between ɛ pl = 7.5 × 10 −5 (Δ ɛ/2 = 0.05%) and ɛ pl = 5 × 10 −4 (Δ ɛ/2 = 0.1%). Loop patches prevail in region B. If the strain amplitude is close to the upper limit of the region B, the loop-patch structure is also predominant in the dislocation structures despite the existence of dislocation walls and a few dislocation cells larger than 2 μm. However, these structures have no significant effect on fatigue failure. The dislocation cells rapidly developed once the plastic strain amplitude is elevated into region C.

The effect of strain ratio on morphology of dislocation in low cycle fatigued SAF 2205 DSS

The effects of strain amplitude and strain ratios in low cycle fatigue (LCF) at 0.25 Hz on the final stable dislocation structure of a failure specimen are investigated in a SAF 2205 duplex stainless steel. The morphology of the fatigued dislocation microstructure in α phase consists of dislocation cell structures and persistent slip bands (PSBs). No dislocation loop patches or labyrinths were observed in the α grains. Instead, persistent slip bands (PSBs) and wormlike PSB loops embedded in a highly dense dislocation matrix were found, and the dislocation density increases with the increase of the strain amplitude and tensile mean strain, which changes the strain ratio. The morphology of fatigued dislocation structure in the γ phase is characterized by the strain-induced martensite.

Cyclic stress–strain behavior of polycrystalline nickel

The influence of strain amplitude and fatigue cycles on cyclic deformation of polycrystalline specimens of commercially 99.53% purity nickel was investigated using fully reversed strain-controlled fatigue tests. The fatigue tests were performed under constant strain amplitude, in air and at room temperature, at a constant strain rate of 0.0001 s−1. The objective was to study cyclic deformation behavior and characterize cyclic hardening response by microstructural observations using transmission electron microscopy. The cyclic stress–strain (CSS) curve of cyclically deformed polycrystalline nickel exhibited three distinct regions with a short quasi-plateau region in the intermediate amplitude range and a slight increase of saturation stress with plastic strain amplitude. The plastic strain amplitude at which the test was conducted influences the cyclic hardening rate. Dislocation structures in fatigued polycrystalline nickel are amplitude dependent and are classified into three types of dislocation structures corresponding to the three regions in the CSS curve. Vein structures consisting of loop patches were observed at low strain amplitudes. These structures become mixed with labyrinth structures at intermediate amplitudes. In addition, persistent slip bands (PSBs) were observed in the quasi-plateau regions of CSS curve. Cellular structures were observed at higher amplitudes which become increasingly equiaxed and smaller with fatigue cycles. A correlation between stress–strain response and development of dislocation structures in deformed polycrystalline nickel revealed that the saturation stress is linearly related to the inverse wall spacing. This relationship is equivalent to the mesh-length theory of work hardening over the strain range used in this study.

The observation of dislocation reversal in front of crack tips of polycrystalline copper after reducing maximum load

The loading at a crack tip varies during fatigue crack propagation. As a result, overloading causes retardation of crack propagation, and underloading causes the acceleration of crack propagation. In addition, reducing the load range by changing either the minimum load or maximum load can cause a reduction or retardation of crack propagation to occur. Examining a fatigue cracked specimen made of polycrystalline copper with back scattered electron images (BEI) in a scanning electron microscope (SEM) revealed that (1) the dislocation structures close to the crack tips gradually evolved from a cell structure into a new loop patch structure during the crack retardation period which follows after reducing the maximum load; (2) restoring the crack propagation rate is a result of re-establishing the cell structure from new loop patches or PSBs; and (3) the evolution of the dislocation structure at the crack tip due to the maximum loading reduction is affected by residual active slip systems.

A study of dislocation evolution in polycrystalline copper during low cycle fatigue at low strain amplitudes

The dislocation structures evolution on the polycrystalline copper at constant strain amplitude during low cycle fatigue is well understood. However, the dislocation structures developments at variable strains, which change from high to low strain amplitude, are seldom reported. In order to realize the dislocation morphology evolution at reduced strain amplitude, the polycrystalline copper is used in this study. The results show that. (1) The S–N curve at reduced strain amplitude from high to low reveals softening, and it is lower than S–N curve which is fatigue in constant strain amplitude at low strain amplitude. (2) The dislocation structures of walls, labyrinth walls, cells or misorientation cells transfer into scattering walls, loop patches or cells. (3) The dislocation morphology development at decreased strain amplitude is determined by the magnitude of reduction in strain amplitude.

Orientation dependence of cyclic deformation behavior and dislocation structure in Ti–5at.% Al single crystals

Cyclic deformation behavior and substructure in single crystal Ti–5at.% Al alloy with different orientations fatigued at Δ ε t/2=0.4% were examined. The selected loading orientation includes: single prism slip, A; double prism slips [ 2 1 ̄ 1 ̄ 0 ], B; pyramidal slip, C; and twinning [0001], D. The testing results show that the crystallographic orientation has a strong effect on the cyclic stress response and the plastic deformation mode of Ti–5at.% Al single crystals. The crystals displayed an initial cyclic hardening followed by a striking softening period, and then a saturation stage was reached in specimens A and B. In contrast, an obvious cyclic saturation stage was obtained after first cyclic hardening until to fracture in specimens C and D. Trace analysis on the surface of specimens with an optical microscope shows that the ( 1 1 ̄ 00 ) single prism slip was operated in specimen A during cycling. The ( 10 1 ̄ 0 ) and ( 1 1 ̄ 00 ) double prism slips can be distinguished from the traces on the (0001) surface in specimen B. The ( 1 1 ̄ 01 ) pyramidal slip and the ( 1 1 ̄ 00 ) prism slip were activated simultaneously in specimen C. Twinning is the primary plastic deformation mode in specimen D. The twinning type includes: { 11 2 ̄ 1 }, { 10 1 ̄ 1 }, { 11 2 ̄ 2 } and { 10 1 ̄ 2 }. The substructure in the fatigued specimens was examined using TEM. Typical dislocation configuration is well developed saturation bundle structure (SBS) in specimen A, while it is the planar edge dislocations which are tangled on the primary ( 10 1 ̄ 0 ) plane and arranged parallel to the [0001] direction in specimen B. Fully developed loop patches were formed in specimen C. Typical deformed structure was the twin bundles and dislocations among twins in specimen D. The effects of plastic deformation mode on the cyclic stress response and the corresponding dislocation configuration of Ti–5at.% Al single crystals are then discussed.

Cyclic deformation of tungsten monofilament-reinforced multicrystalline copper composites

In an attempt to understand the cyclic deformation behavior of continuous fiber reinforced metal matrix composites, plastic strain controlled tests have been performed on tungsten monofilament-reinforced, multicrystalline, copper composites. The cyclic hardening response of the composites greatly depends on the fatigue dislocation structures corresponding to the strain amplitude. For example, at high strain amplitude, i.e. 1×10 −3, secondary slip stimulated by the self-stresses of the primary dislocations becomes more active, and secondary hardening even occurs during saturation. At low strains, loop patches form and are associated with fine slip. At intermediate strains, persistent slip bands occur, but their distribution is altered by the presence of the fiber. The paper introduces a simple model to link the cyclic stress–strain response of the multicrystalline composites to those of monolithic single crystals and fibers. This model not only represents the fiber reinforcement by the rule of mixtures, but also adopts the Sachs model for the single crystal–polycrystal conversion factor. The results calculated by the model show very good agreement with the experimental data in all strain amplitudes at which the composites were fatigued. This encouraging outcome suggests that the new model could be applied to high-cycle fatigue of commercial continuous-fiber-reinforced polycrystalline metal matrix composites.

Cyclic deformation behavior of non-isoaxial copper tricrystals and bicrystals

The cyclic hardening and saturation behaviors of copper tricrystals and bicrystals were investigated in strain-controlled multiple step tests. The results show that, for the inclined grain boundary (GB) bicrystal with single slip components, the cyclic stress strain (CSS) curve exhibits a plateau or quasi-plateau region, while the CSS curve of tricrystals shows no plateau. Observations of surface morphologies indicated that owing to the strain incompatibility of three grains, at lower strain amplitude the triple junction (TJ) retards obviously the primary slip in grains and makes deformation near it smaller than that near the bicrystal GB, while at higher strain amplitude slip can be distributed near the TJ homogeneously. The probability of crack initiation at the same TJ is closely related to the loading direction. The saturation dislocation structures of tricrystal specimens under the strain amplitude of the last step were explored by the electron channeling contrast technique in SEM (ECC-SEM). Loop patches with persistent slip band (PSB) ladders embedded were found even in the TJ vicinity for all grains. Dislocation-free zones (DFZ) occurred in the vicinity of TJ and GB, and the difference in shapes between them is due to the difference in internal stress field. Misoriented cell structure and dislocation wall structure were found near the crack tip, and the formation of them is associated with the cooperative action of crack tip, GB, grain orientation and the applied strain amplitude.

Fatigue fracture at copper bicrystal interfaces: fractography

Abstract The fracture surfaces of intergranular cracks in copper bicrystals with different misorientations, subjected to different mechanical pretreatments and cracking directions, were studied by scanning electron microscopy (SEM). The dislocation structures present before the crack formed and propagated were characterized by transmission electron microscopy (TEM). It was found that they could be either loop patches and persistent slip bands (PSB’s) (single slip) or maze and cell structures (multiple slip) depending on the misorientation and the pretreatment. The results showed that these structures influenced the shape of the crack front, which could be aligned close to specific crystallographic directions or straight depending on the prior structure. The crack propagation direction also influenced the morphology of the crack front, macroscopically and microscopically, due to differences in the multiplicity of slip. These results suggest that, for a ductile metal, the fatigue cracking behavior depends mostly on hardening and overall dislocation structure, even when the crack is propagating intergranularly.

Effect of grain size/texture on the cyclic stress–strain behavior of polycrystalline copper

Abstract The cyclic stress–strain behavior of copper with different grain sizes/textures has been studied. The results show that at high plastic strain amplitudes, secondary hardening occurs after the primary hardening stage in small-grained specimens; and cyclic softening occurs after the primary hardening stage in large-grained specimens. At low plastic strain amplitudes, the effect of grain size/texture is small, saturation occurs after the primary hardening stage in all specimens. The secondary hardening found in small-grained specimens is associated with the formation of equiaxed cells. In a small-grained specimen, it contains more twin and grain boundaries and twin steps than a large-grained specimen; these boundaries and twin steps in particular promote secondary slip activity, therefore enhance the formation of equiaxed cells. The cyclic softening found in large-grained specimens is mainly associated with the condensation of loop patches into dense dislocation walls.

Investigation of dislocation structure in a cyclically deformed copper single crystal using electron channeling contrast technique in SEM

The dislocation structures in a copper single crystal under cyclic straining were studied using electron channeling contrast (ECC) in scanning electron microscopy (SEM). It is shown that the typical dislocation structures observed in the cyclically deformed copper single crystal by means of the ECC technique are in good agreement with those observed by transmission electron microscopy. ECC-SEM observation clearly reveals an evolutional process of dislocation structure from the loop patches of matrix formed at lower strain amplitude to the labyrinth formed at higher strain amplitude. Moreover, the dislocation microstructure in deformation bands, distinctly different from that in the surrounding matrix, was also observed by this technique.

Cyclic hardening mechanisms in [001] copper single crystals

Friction stress and back stress of [001] Cu single crystals during cyclic deformation were derived from cyclic stress–strain hysteresis loops by using the Cottrell method and the results are compared with those for single slip crystals. The cyclic hardening features of the [001] crystals are described in terms of the friction stress and back stress. Specific, detailed study was carried out on the sample cycled with a plastic strain amplitude of 1.8×10 –3. It has been shown that both the ‘true’ friction stress, i.e. the cyclic yield stress, and the back stress in the [001] crystals increase much more rapidly than those in single slip crystals in the hardening stage. In the saturation stage, however, only the friction stress in the [001] crystal is higher than its correspondent in the single slip crystals, while the back stresses in these two types of crystals are close to each other. The higher friction stress in the [001] crystal is related to the higher density of jogs produced by the dislocation reactions between the primary and critical slip systems, and the existence of secondary dislocations in channels. The higher back stress in the hardening stage is attributed to the higher dislocation density in loop patches introduced by dislocation reactions in the first dozen of cycles. By modifying the Kulhlmann-Wilsdorf and Laird model, it is possible now to express quantitatively both the back stress and the shear stress in a cyclically deformed crystal with a particular orientation as functions of the applied strain amplitude as well as an orientation-dependent factor: the hardening coefficient for the first stage of unidirectional deformation. The predictions from these expressions for multiple slip crystals are in very good agreement with experimental data.

THE ELECTRON CHANNELLING CONTRAST TECHNIQUE APPLIED TO THE CHARACTERISATION OF DISLOCATION STRUCTURES IN THE VICINITY OF A FATIGUE CRACK

Abstract— In this investigation the Electron Channelling Contrast (ECC) technique in scanning electron microscopy (SEM) was applied to reveal the dislocation structures in the vicinity of surface fatigue cracks in comparison to those of cyclically‐deformed recrystallized polycrystalline copper. The plastic zone around a fatigue crack was found to consist of an innermost region containing cells, followed by a region containing dense veins and PSBs, surrounded by a structure of loose veins, bundles and loop patches typical of the cyclically deformed matrix. A relation between plastic strain amplitude values deduced from cyclic stress‐strain investigations and the dislocation structures near fatigue cracks are given. Typical regions of damage accumulation were identified and plastic strain contours for surface fatigue cracks established. The essentially non‐destructive ECC technique is particularly suited to identify the changes in mesoscopic dislocation structures from surface layers to the interior of specimens over large specimen areas.

Dislocation structures in cyclically deformed copper bicrystals

Two types of symmetrical copper bicrystals, designated as [135]/[135] and [235]/[235], were cyclically deformed at constant shear strain amplitudes ( γ p1) in the range from ~1.7 × 10 −4 to ~9.1 × 10 −3. Observations showed that the dislocation structures in the plateau regions of the cyclic stress-strain (CSS) curves of the bicrystals are mainly composed of the ladders of persistent slip bands (PSBs) and the loop patches of matrix. However, additional structure types, such as cells, are present at the high end of plateau in the [–35]/[–35] bicrystal. Above the plateau, the dislocation structures are characterized by cells or labyrinths. The dislocation structures in the vicinity of grain boundary were found to be basically similar to those in the bulk of the fatigued bicrystals. Dislocation-free-zones beside grain boundaries were seldom formed under low strain amplitudes and PSBs were observed to become irregular or taper to a point when approaching to a grain boundary.