Experimental study on compression stroke characteristics of free- piston engine generator

The compression stroke characteristics of free-piston engine generator were studied. The numerical model of the compression stroke was established based on thermodynamics and dynamics equation,and the leak loss,heat loss and friction loss were considered. Through solving numerical equations,the in-cylinder pressure of compression stroke under different compression ratios was calculated,energy transfer and conversion process was analyzed,and the calculated results were experimentally verified. The results showed that the actual effective output of electronic energy and the compression energy stored in the com-pressed gas accounted for about 70%. The compression energy gradually increased with the increasing com-pression ratio. When the compression ratio was more than 7. 5,the actual compression energy increased slowly and the energy error between simulation and test decreased.

Ramp-Wave Compression Experiment with Direct Laser Illumination on ShenGuang-Ⅲ Prototype Laser Facility

Ramp-wave compression experiment to balance the high compression pressure generation in aluminum and x-ray blanking effect in transparent window is demonstrated with an imaging velocity interferometer system for any reflector （VISAR） on ShenGuang-Ⅲprototype laser facility. The highest pressure is about 500 GPa after using the multilayer target design Al/Au/Al/LiF and -10^13 W//cm2 laser pulse illuminated on the planar Al target, which generates the spatial uniformity to 〈1% over 500 μm on the ablation layer. A 2-μm-thick Au layer is used to prevent the x-ray from preheating the planar ablation Al layer and window material LiF. The imaging VISAR system can be used to record the abrupt loss of the probe beam （λ= 532 nm） caused by absorption and reflection of 20-μm, 30-μm and 40-μm-thick Al, i.e., the blanking effect. Although there are slight shocks in the target, the peak pressure 500 GPa, which is the highest data up to now, is obtained with ramp-wave compression.

Prediction of Load-Displacement Curve of Flexible Pipe Carcass Under Radial Compression Based on Residual Neural Network

The carcass layer of flexible pipe comprises a large-angle spiral structure with a complex interlocked stainless steel cross-section profile, which is mainly used to resist radial load. With the complex structure of the carcass layer, an equivalent simplified model is used to study the mechanical properties of the carcass layer. However, the current equivalent carcass model only considers the elastic deformation, and this simplification leads to huge errors in the calculation results. In this study, radial compression experiments were carried out to make the carcasses to undergo plastic deformation. Subsequently, a residual neural network based on the experimental data was established to predict the load-displacement curves of carcasses with different inner diameter in plastic states under radial compression.The established neural network model’s high precision was verified by experimental data, and the influence of the number of input variables on the accuracy of the neural network was discussed. The conclusion shows that the residual neural network model established based on the experimental data of the small-diameter carcass layer can predict the load-displacement curve of the large-diameter carcass layer in the plastic stage. With the decrease of input data, the prediction accuracy of residual network model in plasticity stage will decrease.

FLOW STRESS MODELING FOR AERONAUTICAL ALUMINUM ALLOY 7050-T7451 IN HIGH-SPEED CUTTING

The high temperature split Hopkinson pressure bar （SHPB） compression experiment is conducted to obtain the data relationship among strain, strain rate and flow stress from room temperature to 550 C for aeronautical aluminum alloy 7050-T7451. Combined high-speed orthogonal cutting experiments with the cutting process simulations, the data relationship of high temperature, high strain rate and large strain in high-speed cutting is modified. The Johnson-Cook empirical model considering the effects of strain hardening, strain rate hardening and thermal softening is selected to describe the data relationship in high-speed cutting, and the material constants of flow stress constitutive model for aluminum alloy 7050-T7451 are determined. Finally, the constitutive model of aluminum alloy 7050-T7451 is established through experiment and simulation verification in high-speed cutting. The model is proved to be reasonable by matching the measured values of the cutting force with the estimated results from FEM simulations.

Integrated identification method of rheological model of sandstone in Sanmenxia bauxite

Based on the uniaxial compression creep experiments conducted on bauxite sandstone obtained from Sanmenxia,typical creep experiment curves were obtained.From the characteristics of strain component of creep curves,the creep strain is composed of instantaneous elastic strain,ε（me）,instantaneous plastic strain,ε（mp）,viscoelastic strain,ε（ce）,and viscoplastic strain,ε（cp）.Based on the characteristics of instantaneous plastic strain,a new element of instantaneous plastic rheology was introduced,instantaneous plastic modulus was defined,and the modified Burgers model was established.Then identification of direct screening method in this model was completed.According to the mechanical properties of rheological elements,one- and three-dimensional creep equations in different stress levels were obtained.One-dimensional model parameters were identified by the method of least squares,and in the process of computation,Gauss-Newton iteration method was applied.Finally,by fitting the experimental curves,the correctness of direct method model was verified,then the examination of posterior exclusive method of the model was accomplished.The results showed that in the improved Burgers models,the rheological characteristics of sandstone are embodied properly,microscopic analysis of creep curves is also achieved,and the correctness of comprehensive identification method of rheological model is verified.

Axial Compression Behavior and Analytical Method of L-Shaped Column Composed of Concrete-Filled Square Steel Tubes

Based on the characteristics of an L-shaped column composed of concrete-filled square steel tubes, the axial compression experiment and nonlinear finite element analysis were carried out to study the mechanical property of the L-shaped column. The load-displacement curve for the L-shaped column, the deflection and load-strain curves for the mono columns were obtained by the axial compression experiment. The results show that the L-shaped column exhibits a flexural-torsional buckling failure mode. The numerical simulation by the finite element analysis shows that the bearing capacity and failure mode are in accordance with those of the axial compression experiment and the feasi- bility of the finite element analysis is proved. For the calculation of the bearing capacity of the L-shaped column com- posed of concrete-filled square steel tubes, an analytical method is proposed based on the theory of the elastic stability and spatial truss model. The results of the analytical method are in good agreement with those of the axial compression experiment and the finite element analysis.

An interlaminar damage shell model for typical composite structures

Using the plate/shell elements in commercial software,accurate analysis of interlaminar initial damage in typical composite structures is still a challenging issue.To propose an accurate and efficient model for analysis of interlaminar initial damage,the following work is carried out:(A)A higher-order theory is firstly proposed by introducing the local Legendre polynomials,and then a novel shell element containing initial damage prediction is developed,which can directly predict transverse shear stresses without any postprocessing methods.Unknown variables at each node are independent of number of layers,so the proposed model is more efficient than the 3D-FEM.(B)Compression experiment is carried out to verify the capability of the proposed model.The results obtained from the proposed model are in good agreement with experimental data.(C)Several examples have been analyzed to further assess the capability of the proposed model by comparing to the 3D-FEM results.Moreover,accuracy and efficiency have been evaluated in different damage criterion by comparing with the selected models.The numerical results show that the proposed model can well predict the initial interlaminar damage as well as other damage.Finally,the model is implemented with UEL subroutine,so that the present approach can be readily utilized to analyze the initial damage in typical composite structures.

FIXED-POINT CONTINUATION APPLIED TO COMPRESSED SENSING:IMPLEMENTATION AND NUMERICAL EXPERIMENTS

Fixed-point continuation （FPC） is an approach, based on operator-splitting and continuation, for solving minimization problems with l1-regularization：min ｜｜x｜｜1＋uf（x）.We investigate the application of this algorithm to compressed sensing signal recovery, in which f（x） = 1/2｜｜Ax-b｜｜2M,A∈m×n and m≤n. In particular, we extend the original algorithm to obtain better practical results, derive appropriate choices for M and u under a given measurement model, and present numerical results for a variety of compressed sensing problems. The numerical results show that the performance of our algorithm compares favorably with that of several recently proposed algorithms.

Structure design and compression experiment of the supporting node for JUNO PMMA detector

Introduction Jiangmen Underground Neutrino Observation is going to build a huge polymethyl methacrylate(PMMA)detector to hold 20,000 tons of liquid scintillator to capture neutrinos in a 700-m underground cave.This PMMA detector has a spherical shape with an inner diameter of 35.4 m and is supported by an outside stainless steel structure through 590 supporting nodes.The maximum compression force applied to these supporting nodes would be about 150 kN when the detector is running.Method This paper focuses on the design and validation of the PMMA supporting node and compares the effects of two gaskets(round gasket and ring gasket)on the supporting node stress and ultimate compression load.An innovative PMMA supporting node structure is first proposed,and a 1/4 symmetric model with the material nonlinearity and frictional contact boundary is established in the finite element analysis(FEA).Results The FEA results show that the principal stress of the structure is less than 3.5 MPa and the Mises stress is less than 5.5 MPa.The stress and deformation at the groove of the supporting node using the ring gasket are smaller than that using the round gasket.The compression experiments of the supporting node using two types of gaskets were conducted to study the effect of gaskets on the ultimate compression load of supporting node.The ultimate compression load of the supporting node with ring gasket is larger than 900 kN,which is six times of design load.In a comparison of experimental results with FEA,the maximum difference is 15.78%,demonstrating the validity of FEA results.Through the material test of PMMA and experiment of the PMMA supporting node,it is known that PMMA is a brittle material and it is very sensitive to sharp corner defects that should be avoided in the design of PMMA structure.

Experimental Study on Friction in Ferrules during Compression Tuning of Fiber Bragg Grating

The effect of friction in ferules on compression tuning characteristics of fiber Bragg gratings (FBG) was observed and analyzed in this paper. It was demonstrated that the friction would make a non-uniform strain in the FBG and degradations of its reflection spectrum. To avoid the effect, some measures have been applied. Near 9 nm tuning range can be obtained with good spectral performance.

Damage evolution of PμLSE additive-manufactured micro-lattice metastructures: Synchrotron radiation 3D tomography image-based analysis

The manufacturing of additives with projection micro litho stereo exposure(PμLSE)has provided an opportunity for the fabrication of metastructures with complex microstructures at micro-nano resolutions.However,the performance evaluation of as-fabricated metastructures is challenging.The benefit of synchrotron radiation-based 3 D imaging techniques and advanced image processing methods makes it is feasible to study fabrication defects and damage processes of micro-nanoscale bodycentered cubic(BCC)lattices manufactured with PμLSE.First,synchrotron radiation technology is used to capture the structural features inside the micro-lattice samples.Subsequently,several types of statistical defects-based image finite element models are adopted to analyze the failure process of the structure under compression loading.Finally,comparisons between in situ experiments and numerical simulation results are performed for verification.The method of the combined non-destructive testing of synchrotron radiation and image finite element technology provides a robust technique for evaluating the performances of additive-manufactured micro-lattice with complex microstructures.

Modeling of strain-inducedγ→α′phase transformation for 201Cu metastable austenitic stainless steel and its verification in rolling processes

To model the strain-inducedγ→α′phase transformation for the Cr-Mn metastable austenitic stainless steel,the 201Cu steel was chosen as the analytical material and the cylindrical samples of this steel with size ofϕ5 mm×10 mm were compressed at strains of 0.2–0.6 in the temperature range of 25–150℃ and in the strain rate range of 0.1–5.0 s^(−1).The flaky samples were prepared by wire cutting from the cylindrical samples and the volume fraction of the strain-inducedα′phase was detected in the test point of the flaky samples.The volume fraction changing with the process parameters was modeled,and the critical temperatures and the critical strains to preventγ→α′phase transformation were calculated as other different process parameters changed.The linear fitting goodness of the model between the calculated volume fraction values and the tested ones is 0.986 and the validity of the model was verified by application in cold and warm rolling experiments.