A Modified Principal Component Analysis Method for Honeycomb Sandwich Panel Debonding Recognition Based on Distributed Optical Fiber Sensing Signals

The safety and integrity requirements of aerospace composite structures necessitate real-time health monitoring throughout their service life.To this end,distributed optical fiber sensors utilizing back Rayleigh scattering have been extensively deployed in structural health monitoring due to their advantages,such as lightweight and ease of embedding.However,identifying the precise location of damage from the optical fiber signals remains a critical challenge.In this paper,a novel approach which namely Modified Sliding Window Principal Component Analysis(MSWPCA)was proposed to facilitate automatic damage identification and localization via distributed optical fiber sensors.The proposed method is able to extract signal characteristics interfered by measurement noise to improve the accuracy of damage detection.Specifically,we applied the MSWPCA method to monitor and analyze the debonding propagation process in honeycomb sandwich panel structures.Our findings demonstrate that the training model exhibits high precision in detecting the location and size of honeycomb debonding,thereby facilitating reliable and efficient online assessment of the structural health state.

Insight Into the Separation-of-Variable Methods for the Closed-Form Solutions of Free Vibration of Rectangular Thin Plates

The separation-of-variable(SOV)methods,such as the improved SOV method,the variational SOV method,and the extended SOV method,have been proposed by the present authors and coworkers to obtain the closed-form analytical solutions for free vibration and eigenbuckling of rectangular plates and circular cylindrical shells.By taking the free vibration of rectangular thin plates as an example,this work presents the theoretical framework of the SOV methods in an instructive way,and the bisection–based solution procedures for a group of nonlinear eigenvalue equations.Besides,the explicit equations of nodal lines of the SOV methods are presented,and the relations of nodal line patterns and frequency orders are investigated.It is concluded that the highly accurate SOV methods have the same accuracy for all frequencies,the mode shapes about repeated frequencies can also be precisely captured,and the SOV methods do not have the problem of missing roots as well.

Structural Modal Parameter Recognition and Related Damage Identification Methods under Environmental Excitations: A Review

Modal parameters can accurately characterize the structural dynamic properties and assess the physical state of the structure.Therefore,it is particularly significant to identify the structural modal parameters according to the monitoring data information in the structural health monitoring(SHM)system,so as to provide a scientific basis for structural damage identification and dynamic model modification.In view of this,this paper reviews methods for identifying structural modal parameters under environmental excitation and briefly describes how to identify structural damages based on the derived modal parameters.The paper primarily introduces data-driven modal parameter recognition methods(e.g.,time-domain,frequency-domain,and time-frequency-domain methods,etc.),briefly describes damage identification methods based on the variations of modal parameters(e.g.,natural frequency,modal shapes,and curvature modal shapes,etc.)and modal validation methods(e.g.,Stability Diagram and Modal Assurance Criterion,etc.).The current status of the application of artificial intelligence(AI)methods in the direction of modal parameter recognition and damage identification is further discussed.Based on the pre-vious analysis,the main development trends of structural modal parameter recognition and damage identification methods are given to provide scientific references for the optimized design and functional upgrading of SHM systems.

Determination of energy coupling to material in laser welding by a novel “sandwich” method

A mathematical energy coupling model was developed to analyze the light transmission in the keyhole and energy distribution on the keyhole wall.The main characteristics of the model include：1） a prototype of the keyhole and the inverse Bremsstrahlung absorption coefficient in the keyhole plasma are obtained from the experiments;2） instead of using a parallel incident beam,a focused laser beam with real Gaussian intensity distribution is implemented;3） both Fresnel absorption and inverse Bremsstrahlung absorption during multiple reflections are considered.The calculation results show that the distribution of absorbed laser intensity by the keyhole wall is not uniform.The maximum laser energy is absorbed by the bottom of the keyhole,although no rays irradiate directly onto the bottom.According to analysis of beam focusing characteristics,the location of the focal plane plays a more important role in the laser energy absorption by the front wall than by the rear wall.

PBL-Sandwich混合教学模式在临床分子生物学检验技术实习教学中的应用

目的 探讨以问题为基础的教学法(PBL)-Sandwich混合教学模式在临床分子生物学检验技术实习教学中的应用效果。方法 选取2018-2019年进入该院分子生物学实验室实习的82例实习生作为研究对象。以2018年的42例实习生作为对照组,采用传统教学模式;以2019年的40例实习生作为试验组,采用PBL-Sandwich混合教学模式。实习结束后,采用理论考试、操作考核和问卷调查等形式评价实习生的教学效果。结果 试验组的理论考试成绩与操作考核成绩均明显高于对照组,差异均有统计学意义(P<0.05)。共发放调查问卷82份,回收有效问卷80份,其中试验组39份,对照组41份,有效回收率为97.56%(80/82)。试验组在提高学习主动性、激发学习兴趣、增强师生间的交流和互动、提升分析解决临床实际问题能力和教学方法实施满意度方面均优于对照组,差异均有统计学意义(P<0.05)。结论 PBL-Sandwich混合教学模式能有效激发实习生学习兴趣,培养实习生自主学习的主观能动性,提高分析、解决临床实际问题能力,教学质量得到提升。

基于微课嵌入的Sandwich教学法在诊断病理学教学中的应用

目的:探讨基于微课嵌入的Sandwich教学法在诊断病理学教学中的应用效果。方法:选取3个班级,随机分为试验组、对照组和空白对照组,分别采用不同的教学方法进行教学。结果:试验组学生的成绩显著优于对照组和空白对照组;试验组学生对该教学方法的认可度较高,教师对试验组学生的课堂表现评价也较高。结论:基于微课嵌入的Sandwich教学模式在诊断病理学教学中具有良好的应用效果,值得进一步推广。

MDT+Sandwich教学法在本科内科学教学中的应用

目的探讨多学科诊疗(MDT)+“三明治”教学法(Sandwich教学法)与传统的以学科为基础的教学法在本科内科学教学中的应用效果。方法选取五年制临床医学专业60名本科生为研究对象,随机分为对照组(n=30)和试验组(n=30)。对照组采用传统的以学科为基础的教学法,试验组采用MDT+Sandwich教学法,课程结束后比较两组教学效果。结果试验组理论考试、临床技能操作考核成绩及课堂教学效果均优于对照组。结论在内科学教学中引入MDT+Sandwich教学法,能够更好地培养学生分析和解决临床问题能力。

基于CBL+PBL联合Sandwich教学法在神经病学本科教学中的探索

神经病学是一门理论性和实践性较强的综合性学科,对从业人员的专业知识和操作技能均有较高要求。传统神经病学本科教育存在教师单方面授课无法激发学生学习兴趣、学生学习有效性不足等问题,使神经病学专业人才的培养存在一定难度。该文基于神经病学本科教学的实际情况,探讨以CBL、PBL联合Sandwich教学法在神经病学专业本科教育体系中的应用前景。

案例教学法联合Sandwich教学法在老年科教学中的应用

目的探讨案例教学法联合Sandwich教学法在老年科教学中的应用效果。方法选取2022年3月—2023年6月潍坊医学院附属医院的60名参加老年科教学的学生为研究对象,按照随机数表法分为两组,各30名。对照组行常规教学,观察组行案例教学法联合Sandwich教学法教学,比较两组教学效果。结果观察组各项模拟出科考试成绩高于对照组,差异有统计学意义(P均<0.05);观察组对实习教学效果的各项满意度评分高于对照组,差异有统计学意义(P<0.05)。结论案例教学法联合Sandwich教学法可提升老年科教学的效果,并提高学生对实习教学效果的满意度。

Sandwich联合角色扮演教学法在住培医师医患沟通能力培训中的应用

目的 以腰椎穿刺术前谈话为例,探讨Sandwich联合角色扮演教学法在住院医师规范化培训(住培)学员医患沟通能力培训中的应用价值。方法 选取2019年3月至2023年1月在该院神经外科进行住培的40名学员,将其分为A、B组,每组20名。A组通过传统教学方法进行腰椎穿刺术前谈话的教学,B组运用Sandwich联合角色扮演教学法进行教学,在教学前、中、后期分别使用医患沟通技能评价量表对2组学员进行考评,最后对2组学员进行满意度问卷调查,对比2组教学效果及学员对教学的满意度。结果 2组学员在教学前测评得分均较低,在教学后测评较教学前均有提升,差异均有统计学意义(P<0.05);与A组比较,B组在教学中期测评得分明显更高,差异有统计学意义(P<0.05);2组在教学后期测评得分比较,差异无统计学意义(P>0.05)。B组住培学员的满意度高于A组,差异有统计学意义(P<0.05)。结论 Sandwich联合角色扮演教学法能快速提升学员的术前谈话沟通能力,也能提高学员的教学满意度,适合在相关教学活动中推广。

Sandwich教学法融入思政教育在超声诊断学中的应用

研究Sandwich教学法融入思政教育模式在超声诊断学教学中应用效果。方法 选择2022年11月-2023年11月在本院接受超声诊断学教学的学生40名,随机分组法分作试验组(Sandwich教学法融入思政教育模式)和对照组(传统教学模式),每组20名,分析不同教学模式的实施效果评价。结果 出科时,试验组考核成绩明显高于对照组,P<0.05;试验组综合能力和批判性思维能力均优于对照组,P<0.05。结论 超声诊断学教学中实施Sandwich教学法融入思政教育模式,可明显提升学生考核成绩、综合素质以及批判性思维能力,可以应用于超声诊断学教学。

Dynamic Response of the U-Typed Sandwich Panel Under Explosion Load Based on the SDOF Method

Sandwich panel is commonly used in ship and marine engineering equipment,such as side structure and superstructure deck of a ship,which is of good anti-explosion performance.This paper addresses a study on the dynamic response of the U-typed sandwich panel under explosion load through the numerical simulation and theoretical methods.Based on the orthotropic plate theory,the U-typed sandwich panel is simplified and transformed into a single degree of freedom(SDOF)spring system,the equivalent motion equation of the SDOF system and the expression of triangular explosion load function are established based on the SDOF theory,and the maximum response spectrum of the SDOF system is obtained.Then,the response of the equivalent SDOF system of the U-typed sandwich panel under explosion load is analyzed,and the theoretical results match well with the numerical simulation results,which verifies the accuracy of the theoretical method proposed in this paper.The theoretical method proposed in this paper could have good engineering applications for the structural anti-explosion design,and provide a reference for the evaluation of the anti-explosion performance of ship and offshore platform structures.

A Mini Review on Testing Methods for Mechanical Properties of Natural Fibre Honeycomb Sandwich Structure and Fractography Analysis

This paper is a review of the past research of mechanical testing methods for natural fibre honeycomb sandwich structure as well as failure modes analysis at a microscopic level by using Scanning Electron Microscope (SEM). As the world is garnering attention towards renewable resources for environmental purposes, studies of natural fibre have been increasing as well as the application of natural fibre throughout various industries such as aerospace, automobiles, and construction sectors. This paper is started with brief information regarding the honeycomb sandwich structure, introduction to natural fibre, its applications as well as the factors affecting the performances of the structure. Next, the mechanical testing methods are listed out as well as the expected outcomes obtained from the respective testing. The mechanical properties are also identified by conducting lab tests according to the ASTM standard for sandwich and core structures. The microstructure of the deformed samples is then examined under Scanning Electron Microscope (SEM) by using different magnifications to study the failure mechanisms of the samples. The images obtained from the SEM test are analyzed by using fractography which will show the failure modes of the samples. This article is based on past research conducted by professional on the related topic.

Sandwich教学方法在非本专业医学本科生临床见习中的应用效果

目的:探讨Sandwich教学方法应用于非麻醉专业本科生在麻醉临床见习中的应用效果。方法:本研究选择2021年4月在首都医科大学附属北京佑安医院参与临床麻醉学见习的51名本科护理学专业学生作为观察对象,根据随机表随机分为对照组(n=26)和试验组(n=25)。其中对照组采用常规的见习教学方法,而试验组采用Sandwich教学方法,最后两组采用理论知识试卷和满意度调查表进行教学效果和教师满意度评价。结果:理论知识掌握方面,试验组和对照组的平均得分分别是(81.80±5.02)分与(66.56±5.13)分,差异具有统计学意义(P<0.05);对见习带教老师满意度方面,试验组显著高于对照组,差异具有统计学意义(P<0.05)。结论:Sandwich教学方法不仅有利于见习生掌握教学大纲内容,而且还有利于提高学生对带教老师的满意度。

含根量对SANDWICH形加筋土界面剪切强度影响--以红叶石楠为例

SANDWICH形加筋土是一种采用粘土夹砂层以及土工格栅而形成的混合填料形式的加筋土结构。采用一系列直接剪切试验研究含根量、竖向应力等因素对筋土界面强度的影响。试验证明,根系的加入对SANDWICH形加筋土界面最大剪应力有所提升且随着竖向应力的增大,土体抗剪强度增幅大。随着粘土中含根量的增加,筋土界面最大剪应力在不同竖向应力作用下出现先增后减的趋势。根据试验数据,利用拟合软件提出了评价筋土界面剪切强度的经验公式,得出理论上含根量的最优值为4.2%。并通过试验验证了拟合公式的有效性和正确性。

PMI Foam Cored Sandwich Components Produced by Means of Different Manufacturing Methods

The paper introduced the structural applications with PMI (Polymethacrylimide) foams in sandwich components for rotor craft, launching vehicle and civil aircraft and discuss some typically used manufacturing methods, such as e.g. in-mould pressing, autoclave curing and resin infusion. The advantages of foam-cored sandwich design versus honeycomb-cored design will be discussed, focussing on manufacturing costs.

THE COMPLEX VARIABLE BOUNDARY ELEMENT METHOD FOR SOLVING SANDWICH PLATE PROBLEMS

The objective of this paper is to develop a new complex variable boundary element method for sand- wich plates of Reissner's type and Hoff's type. The general solution of Helmhotz equation in complex field is given. Based on the Vekua's complex integral representation of the analytic function, the new boundary integral equations are formulated. The density function in the integral equation is determined directly by boundary element method. Some standard examples are presented, and the results of numerical solutions are accurate everywhere in the plate. The approach presented is only applicable for bounded simply connected regions.

An Optimum Analysis Method of Sandwich Structures Made from Elastic-viscoelastic Materials

Due to a viscoelastic damping middle layer,sandwich structures have the capacity of energy consumption.In this paper,we describe the frequency-dependent property of viscoelastic materials using complex modulus model,and iterative modal strain energy method and iterative complex eigenvalue method are presented to obtain frequency and loss factor of sandwich structures.The two methods are effective and exact for the large-scale complex composite sandwich structures.Then an optimum analysis method is suggested to apply to sandwich structures.Finally,as an example,an optimum analysis of a clamped-clamped sandwich beams is conducted,theoretical closed-form solution and numerical predictions are studied comparatively,and the results agree well.

Mechanical Performance of Bio-inspired Bidirectional Corrugated Sandwich Pressure Shell Under External Hydrostatic Pressure

This paper aims to enhance the compression capacity of underwater cylindrical shells by adopting the corrugated sandwich structure of cuttlebone.The cuttlebone suffers uniaxial external compression,while underwater cylindrical shells are in a biaxial compressive stress state.To suit the biaxial compressive stress state,a novel bidirectional corrugated sandwich structure is proposed to improve the bearing capacity of cylindrical shells.The static and buckling analysis for the sandwich shell and the unstiffened cylindrical shell with the same volume-weight ratio are studied by numerical simulation.It is indicated that the proposed sandwich shell can effectively reduce the ratio between circumferential and axial stress from 2 to 1.25 and improve the critical buckling load by about 1.63 times.Numerical simulation shows that optimizing and adjusting the structural parameters could significantly improve the advantage of the sandwich shell.Then,the hydrostatic pressure tests for shell models fabricated by 3D printing are carried out.According to the experimental results,the overall failure position of the sandwich shell is at the center part of the sandwich shell.It has been found the average critical load of the proposed sandwich shell models exceeds two times that of the unstiffened shell models.Hence,the proposed bio-inspired bidirectional corrugated sandwich structure can significantly enhance the pressure resistance capability of cylindrical shells.

A Review on Sources,Extractions and Analysis Methods of a Sustainable Biomaterial:Tannins

Condensed and hydrolysable tannins are non-toxic natural polyphenols that are a commercial commodity industrialized for tanning hides to obtain leather and for a growing number of other industrial applications mainly to substitute petroleum-based products.They are a definite class of sustainable materials of the forestry industry.They have been in operation for hundreds of years to manufacture leather and now for a growing number of applications in a variety of other industries,such as wood adhesives,metal coating,pharmaceutical/medical applications and several others.This review presents the main sources,either already or potentially commercial of this forestry by-materials,their industrial and laboratory extraction systems,their systems of analysis with their advantages and drawbacks,be these methods so simple to even appear primitive but nonetheless of proven effectiveness,or very modern and instrumental.It constitutes a basic but essential summary of what is necessary to know of these sustainable materials.In doing so,the review highlights some of the main challenges that remain to be addressed to deliver the quality and economics of tannin supply necessary to fulfill the industrial production requirements for some materials-based uses.