Stretch Processing Research Articles

Experimental investigation on in-plane shear behavior of E-glass fiber/epoxy laminated composites under different strain rates

Glass fiber reinforced polymer (GFRP) has been widely applied in buildings and bridges owing to its excellent material properties. The GFRP as a bearing load component in structures may be damaged, with an increasing threat from accidental impact. To understand the dynamic in-plane shear properties of GFRP is essential, which is a basis to design and evaluate structures. In this study, the ±45° specimens of GFRP laminated were tested to investigate the in-plane shear properties with the strain rate from quasi-static to 106 s−1. The dynamic test was conducted by INSSTRON VHS and the stretch process was record by high-speed camera. The Digital Image Correlation (DIC) method was used to obtain strains of the specimens. And the field-emission scanning electron microscopy (SEM) technique was used to observe the fracture surface of the specimen. The results indicated that the failure mode, shear strength, failure strain, failure strain, absorbed energy and shear modules possessed strain rate effects. Furthermore, the empirical equations were proposed, which can be used to predict the dynamic increase factor at different loading rate.

Uniform stretching behavior of single crease origami arrays

Origami arrays featuring ideal purely rotational creases inherently possess multiple kinematic degrees of freedom. The incorporation of crease rotational stiffness introduces additional constraint relations to the kinematic morphology of the origami array, due to the interaction between the plate and the crease. This paper concentrates on elucidating the coupling effect, employing two theoretical models to systematically analyze the uniform stretch process of single crease origami arrays. The validity of our theoretical approaches is substantiated through verification in the finite element method. Firstly, the mechanical equations of the origami unit, together with the length and angle constraint equations of the origami array, are amalgamated to formulate a comprehensive set of morphological computational equations specific to the single crease origami array. This set enables the realization of morphological analysis for general origami arrays. Moreover, energy equations for the origami array are computed using an equivalent rigid plate nonlinear creasing element. When combined with constraint equations corresponding to horizontal stretch displacement, these energy equations contribute to the establishment of a nonlinear optimization framework for determining the morphology of uniform single crease origami arrays. Notably, our investigation reveals that during the early stages of the unfolding process for a single crease origami array, even a small relative horizontal stretch displacement can induce a drastic change in the center crease. Through finite element analysis of general origami arrays, it is shown that the proposed theoretical analysis method applies to different crease stiffness, both unfolding and folding processes, and different plate types. The research method in this paper can provide ideas for systematically analyzing the influence mechanism of crease properties on the morphological features of origami structures.

Ultrahigh energy density in dielectric nanocomposites by modulating nanofiller orientation and polymer crystallization behavior

High-energy density dielectrics for electrostatic capacitors are in urgent demand for advanced electronics and electrical power systems. Poly(vinylidene fluoride) (PVDF) based nanocomposites have attracted remarkable attention by intrinsic high polarization, flexibility, low density, and outstanding processability. However, it is still challenging to achieve significant improvement in energy density due to the common contradictions between electric polarization and breakdown strength. Here, we proposed a novel facile strategy that simultaneously achieves the construction of in-plane oriented BaTiO3 nanowires and crystallization modulation of PVDF matrix via an in-situ uniaxial stretch process. The polar phase transition and enhanced Young's modulus facilitate the synergetic improvement of electric polarization and voltage endurance capability for PVDF matrix. Additionally, the aligned distribution of nanowires could reduce the contact probability of nanowire tips, thus alleviating electric field concentration and hindering the conductive path. Finally, a record high energy density of 38.3 ​J/cm3 and 40.9 ​J/cm3 are achieved for single layer and optimized sandwich-structured nanocomposite, respectively. This work provides a unique structural design and universal method for dielectric nanocomposites with ultrahigh energy density, which presents a promising prospect of practical application for modern energy storage systems.

A Low-Cost Wideband Digital Array Antenna Based on Stretch Processing Technique

Wideband digital phased array radar offers the advantages of high range resolution, which improves the recognition ability for multiple targets, group targets, and high-speed targets. Traditional wideband phased arrays use true time delay to compensate for aperture fill time; however, the cost increases significantly. In this paper, a wideband elemental digital array architecture based on the stretch processing method is proposed. By utilizing the time-domain and frequency-domain translation equivalence of the LFM (Linear Frequency Modulation) signal waveform, the equivalent aperture fill time is compensated for through frequency shift and phase shift after stretch processing. Compared to traditional wideband digital arrays, this method can dramatically reduce the required sampling rate and lower the requirements on antenna hardware, thereby reducing the manufacturing cost of system. A comprehensive analysis of the signal processing process and stretch processing method is provided. And an antenna array prototype is developed to verify the T/R channel compensation and wideband beamforming. Measured results show that the antenna is capable of ±60° scanning in azimuth plane and ±40° scanning in elevation plane, with a bandwidth of 500 MHz in S-band. The results demonstrate excellent wideband beam performance and accurate lobe scanning, which confirms the validity of the proposed wideband architecture for stretch processing, frequency shift, and phase shift. This method can be widely applied to the low-cost design and wideband performance improvement of wideband digital array radar.

Cooperative anti-jamming algorithm for networked radars based on stretch processing

Cooperative anti-jamming algorithm for networked radars based on stretch processing

Investigation on the Correlation between Biaxial Stretching Process and Macroscopic Properties of BOPA6 Film.

Biaxially oriented polyamide 6 (BOPA6) films were prepared by extrusion casting and biaxial stretching with polyamide 6. The effects of different biaxially oriented on the macroscopic properties of BOPA6 were investigated by characterizing the rheological, crystallization, optical, barrier and mechanical properties. The results show that the increase of stretching temperature leads to the diffusion and regular stacking rate of BOPA6 chain segments towards crystal nuclei increases, the relative crystallinity increases, reaching 27.87% at 180 °C, and the mechanical strength and optical performance decrease. Heat-induced crystallization promotes the transformation of β-crystals to α-crystals in BOPA6, resulting in a more perfect crystalline structure and enhancing oxygen barrier properties. BOPA6 chains are oriented, and strain-induced crystallization (SIC) occurs during the biaxial stretching. Further increasing the stretch ratio, the relative crystallinity increased to 30.34%. The machine direction (MD) and transverse direction (TD) tensile strength of BOPA6 (B-33) are nearly two times higher than the unstretched film, reaching 134.33 MPa and 155.28 MPa, respectively. In addition, the permeation decreases to 57.61 cc·mil/(m2 day), and the oxygen barrier performance has improved by nearly 30% compared to the sample B-22. BOPA6 has a high storage modulus at a high stretching rate (300%/s). Rapid chain relaxation would promote the molecular chain disorientation, destroy the entangled network of the molecular chain, and lead to a decrease in tensile strength, reducing to about 110 MPa.

Structural Evolution of High-Entanglement Ultrahigh Molecular Weight Polyethylene Films with Reserved Shish Crystals during the Hot Stretching Process

Structural Evolution of High-Entanglement Ultrahigh Molecular Weight Polyethylene Films with Reserved Shish Crystals during the Hot Stretching Process

Optical Z-Plate Compensation Film Manufactured by In-Plane Stretching Process to Improve Display Quality of OLEDs

Optical Z-Plate Compensation Film Manufactured by In-Plane Stretching Process to Improve Display Quality of OLEDs

High-performance carbon-based nanomaterial composites for ultrafast lasers based on stretch processing

Carbon-based nanomaterials, and specifically carbon nanotube and graphene, have been widely used as saturable absorber (SA) in ultrafast fiber laser. However, the performance of these SAs is limited due to the low damage threshold or self-starting capability. In our work, we have proposed a novel and straightforward method for enhancing the optical performance of polyvinyl alcohol-based carbon nanotube and graphene composite film. By mechanical stretching the composite films, the damage threshold of carbon nanotube-based SA and the self-starting capability of graphene-based SA can be obviously improved. The distinct nonlinear optical properties of carbon nanotube and graphene are analyzed, and the mode-locking performance is compared. Our finding provides a new insight and experimental basis for the development of high-performance carbon-based nanomaterial mode locker for ultrafast fiber lasers.

Proposed SAR range focusing algorithm based on simulation analysis and SDR implementation

Synthetic aperture radar (SAR) imaging systems use pulse focusing techniques for achieving fine range resolution and large range detection. Stretch processing and correlation pulse focusing techniques are the most popular algorithms used in the radar signal processing stage. The architecture of the stretch processing technique makes it commonly used in frequency modulated continuous wave (FMCW) radar systems due to its simple architecture, low sampling rate, and inexpensive hardware. This paper discusses how the stretch range focusing approach can be used instead of the matched filter technique in the processing stage of the SAR Range-Doppler algorithm (RDA) to generate images of finer resolution and higher quality. In addition, validating the proposed algorithm and evaluating its performance according to some evaluation indices such as peak sidelobe ratio (PSLR), integrated sidelobe ratio (ISLR), and the impulse response width (IRW). Also, this paper presents a comprehensive analysis and hardware implementation of the two SAR algorithms, based on software-defined radio (SDR) architecture where it is characterized by less complexity, low cost, and high flexibility due to the usage of both software data processing and software waveform generation. Two Universal Software Radio Peripheral (USRP-2932) and NI-LabVIEW® software development environment are the platforms used for the hardware validation process. The transmitted waveform is a linear frequency modulated (LFM) signal generated by the first USRP (transmitter) which will hit a target located at a certain distance. The second USRP is used as a receiver for target’s echo processing and detection. This processing stage contains two architectures, which are the matched filter pulse compression architecture and the stretch range focusing approach. Finally, the validation process of the hardware results is performed based on the pre-mentioned evaluation indices.

Minute-Scale Evolution of Free-Volume Holes in Polyethylenes during the Continuous Stretching Process Observed by In Situ Positron Annihilation Lifetime Experiments

Using the newly developed positron annihilation lifetime spectroscopy (PALS) facility with a high count rate up to 3000 cps, in situ PALS experiments were performed for the first time on the continuous stretching process of polymers to quantitatively analyze the minute-scale evolution of free-volume holes. According to the stress–strain relationship and PALS results of four types of polyethylenes with different crystallinities, the tensile process could be divided into four distinct stages: elastic, initial nonlinear (until yield point), postyield, and strain hardening stages. The increase of o-Ps (orthopositronium) lifetime in the first three stages exhibits an enlargement of free-volume hole size with increasing strain. The decrease of the o-Ps lifetime in the last stage is most probably due to the increasing anisotropy of free-volume holes. The relative fractional free volume FFVr (derived from hole radius R (calculated from the Tao–Eldrup model) and o-Ps intensity) generally increases in the first two stages but remains nearly unchanged in the other two stages. This work demonstrates a new feasibility to disclose minute-scale evolution of microstructure of materials through in situ PALS experiments in the future.

Method of 2-D Range-Doppler Imaging for Plasma Wake Based on Range Walk Correction

When a hypersonic vehicle flies in the atmosphere, plasma sheath and trails are configured around the vehicle due to aerodynamic heating and ablation, which distort the radar echo signal and then influence the target range information and Doppler frequency extracted from the echoes. In order to examine the impact of plasma laminar wake on radar detection, this article is primarily aimed to establish a laminar wake echo model based on a linear frequency-modulated continuous wave (LFMCW) radar, which takes into account the reaction control system of laminar wake by employing the Born approximation solution and the characteristics of the inhomogeneous and nonunique velocity of the wake medium. An echo signal processing method is also developed, in which the stretch processing technique is combined with the keystone transform of the target range walk correction. Such a treatment not only reduces the sampling rate and bandwidth, but also eliminates the cross-range cells phenomenon caused by hypersonic; finally, the range-Doppler (RD) image of the wake is achieved by 2-D fast Fourier transform (2-D FFT) processing, and radar range and velocity measurement results in the presence of plasma are obtained.

All-Optical Fourier-Domain-Compressed Time-Stretch Imaging with Low-Pass Filtering

Optical time-stretch (OTS) imaging has shown significant advantages in many applications, such as high-throughput cell screening, for its high frame rate and the capability of continuous image acquisition. Unfortunately, its application in practice is fundamentally limited by the pressure on data transmission and storage caused by the extreme throughput. Compressed sensing (CS) has been considered a promising approach to solve this problem by recovering the signal at a sampling rate significantly lower than the Nyquist sampling rate. However, the temporal stretch and compression processes, which are currently realized with two sections of dispersive media with complementary GVD, make the system complex and introduce notable power loss to the system, leading to a low signal-to-noise ratio (SNR). In this work, we propose and demonstrate all-optical Fourier-domain-compressed time-stretch imaging with low-pass filtering. Only one section of dispersive media is needed to temporal stretch the pulse, while the compression of the stretched pulses is achieved with low-pass-filtering after optical-electrical conversion. Therefore, the structure of the system is notably simplified, and the SNR or the quality of the images can be improved. The principle of this method is theoretically analyzed, and its performance is experimentally demonstrated. The results show that our system can image flowing cells at a high flowing speed of 1 m/s, with a spatial resolution of 2.19 μm on condition that the original data are compressed by 80%. Our method can boost the application of OTS imaging in the fields where high-throughput and real-time imaging is required.

Fractional Fourier Transform Receiver for Modulated Chirp Waveforms

A novel receiver structure for the reception of linearly frequency modulated (LFM) chirps carrying additional narrowband (phase) modulation is proposed. A linear relation between the time delay and the beat frequency shift of the target response in stretch processing is exploited to estimate the target range via correlation of the received signal with the replica in a Fractional Fourier Transform (FrFT) domain. According to numerical simulations, the proposed FrFT receiver demonstrates improved performance and computational efficiency over the state-of-the-art solutions for the moderate-to-large bandwidth of the information-carrying modulation. The receiver was integrated into the waveform-agile radar polarimetric agile radar in S band (PARSAX) and its performance has also been verified experimentally.

A High-Resolution Imaging Method for ISAR Based on Sparse Reconstruction

For the problem of first-order and second-order range migration in ISAR imaging under the condition of wide angle and wide bandwidth, a method for sparse azimuth data is proposed to obtain high-resolution ISAR images. After stretch processing, envelope alignment and residual video phase removal, the sparse recovery algorithm that sparse base is constructed by the Keystone transform is used to achieve range migration correction and the missing range profile reconstruction, and then the second-order phase estimation method based on fractional Fourier transform is used to estimate and compensate the second-order rotational phase. Simulation results show the method can effectively improve the imaging quality.

Oil drop stretch and rupture behavior at throat and pore junction during imbibition with active nanofluid: A microfluidic approach

Imbibition is an effective method to recover oil from small pore and throat. Here we report the formation of oil drop at pore and throat junction during spontaneous imbibition with active nanofluid. A T-channel microfluidic model combined with high-speed camera was used to observe the stretch and rupture process of oil discharged from throat to pore. When oil drop was discharged from throat gradually, its width/length was kept deceasing before rupturing. With more active content in the aqueous phase, the interfacial tension decreased from 33.8 to 8.7 mN/m, and the oil recovery increased by 12.4% by spontaneous imbibition. The oil drop rupture frequency increased by 3.0 times, but the length and width of the oil drop decreased by 32.2% and 28.0%, respectively. The reduced size of the oil drop would benefit the oil transportation in porous media. Higher flow rate in pores and throat would all intensify rupturing of the oil drop. Moreover, small throat could further reinforce the rupturing process. From combination of fluid flow rate, interfacial tension, and viscosity, higher capillary number reduced the maximum dimensionless width and length of the oil drop by 44.3% and 42.7%, respectively. The reduced size of oil drops ruptured at pore and throat junction contributes to the transportation of oil in porous media. Overall, this study provides a basic theory for active nanofluid to enhance imbibition oil recovery in tight reservoirs.

Influence of Prereserved Shish Crystals on the Structural Evolution of Ultrahigh-Molecular Weight Polyethylene Films during the Hot Stretching Process

Influence of Prereserved Shish Crystals on the Structural Evolution of Ultrahigh-Molecular Weight Polyethylene Films during the Hot Stretching Process

HMGB1 in macrophage nucleus protects against pressure overload induced cardiac remodeling via regulation of macrophage differentiation and inflammatory response

Pressure overload induced cardiac remodeling is associated with a complex spectrum of pathophysiological mechanisms. As inflammatory cells, macrophages maintain a critical position in mechanical stress-induced myocardial remodeling. HMGB1 is a highly conserved, ubiquitous protein in various types of cells whose biological roles are closely dependent on subcellular sites. However, whether HMGB1 expressed in macrophages performs the protective or pathological responses in cardiac remodeling is unknown. In this study, we generated the myeloid-specific HMGB1 knockout mice and detected the effects of macrophage HMGB1 in response to pathophysiological stress. Our data showed HMGB1 in macrophages played a protective role against the pressure overload induced cardiac pathophysiology. The deletion of HMGB1 in macrophages gains more differentiation of M1-type pro-inflammatory macrophage during the mechanical stress-induced myocardial remodeling, thereby aggravating the inflammatory response in whole heart, resulting in accelerated deterioration of cardiac function. Moreover, in vitro data also validated HMGB1 got involved in the process of macrophage polarization. Macrophages without HMGB1 are more inclined to differentiate into M1 during the stretch process. In summary, the present results indicated that loss of HMGB1 in macrophages can exacerbate heart failure through increased differentiation of pro-inflammatory macrophages and enhanced inflammatory response.

Insights into Gradient and Anisotropic Pore Structures of Capiox® Gas Exchange Membranes for ECMO: Theoretically Verifying SARS-CoV-2 Permeability.

When using the extracorporeal capillary membrane oxygenator (sample A) for ECMO treatments of COVID-19 severely ill patients, which is dominantly used in Japan and worldwide, there is a concern about the risk of SARS-CoV-2 scattering from the gas outlet port of the membrane oxygenator. Terumo has launched two types of membranes (sample A and sample B), both of which are produced by the microphase separation processes using polymethylpentene (PMP) and polypropylene (PP), respectively. However, the pore structures of these membranes and the SARS-CoV-2 permeability through the membrane wall have not been clarified. In this study, we analyzed the pore structures of these gas exchange membranes using our previous approach and verified the SARS-CoV-2 permeation through the membrane wall. Both have the unique gradient and anisotropic pore structure which gradually become denser from the inside to the outside of the membrane wall, and the inner and outer surfaces of the membrane have completely different pore structures. The pore structure of sample A is also completely different from the other membrane made by the melt-extruded stretch process. From this, the pore structure of the ECMO membrane is controlled by designing various membrane-forming processes using the appropriate materials. In sample A, water vapor permeates through the coating layer on the outer surface, but no pores that allow SARS-CoV-2 to penetrate are observed. Therefore, it is unlikely that SARS-CoV-2 permeates through the membrane wall and scatter from sample A, raising the possibility of secondary ECMO infection. These results provide new insights into the evolution of a next-generation ECMO membrane.

Orientation and Mechanical Properties of Extrusion Cast PA 12 Films in Biaxial Stretching Process

Abstract The levels in biaxial orientations and mechanical properties of stretched extrusion cast polyamide 12 films were investigated with birefringence, wide angle X-ray diffraction (WAXD) pole figure and mechanical testing. Introduction of a pseudo-orthogonal crystalline symmetry enabled the calculation of White-Spruiell biaxial orientation factors using WAXD pole figure data. The orientation was uniaxial or biaxial depending on the stretch ratios along two principal stretching directions that are the machine direction (MD) and the transverse direction (TD). According to the WAXD pole figure patterns, planar alignments of hydrogen bonded layers were formed with respect to the film surface from most of the stretched films. Balanced stretching at higher stretch ratios enhanced the planarity. It was found that the mechanical properties (tensile strength and elongation at break) of the films had a close correlation with the out-of-plane birefringences.