Three-dimensional photoelasticity analysis of Nitinol Patellar Concentrator for treating patellar fractures

Objective: To analyze the biomechanical elements of Nitinol Patellar Concentrator (NT-PC) in heating commi nuted patellar fractures. Methods: The epoxy resin three dimensional photoelasticity pobal model was loaded with Nitinol Patellar Connector and frozen. After dividing layer, photographing and tracing, iterative method was used to calculate the stress value of every tuteed node. Rasults: Stress values of 1 262 nodes scattered in 12 layers were obtained The stress distribution indicated that an overall stress field was yield when the NT-PC fixated the patellar model, and there existed fixative stress in the facies articularis and distal pole of the patellar model. Conclusion: The NT-PC has evident therapeutic effect for the comminuted patellar fractures. The existing stress is helpful in maintaining anatomical reduction and enhancing fracture healing.

THE VARIATIONAL PRINCIPLES OF COUPLED SYSTEMS IN PHOTOELASTICITY

This paper presents an energy principle, zero different principle of coupledsystems in photoelasticity, from which the potential energy, the complementary energy,generalized potential energy and generalized complementary energy variationalprinciples of the coupled systems in photoelasticity are derived What is called the coupled systems means that two deformational bodies, forwhich figures, sizes,loads and boundary conditions are the same and they are all inactual states but they are made of different materials.Prototype body and model body in photoelasticity are essentially the coupledsystems, therefore the above principles become the theoretical basis of defining theinflunce of Poissons ratio v on accuracy of the frozen-stress method.

High-precision stress determination in photoelasticity

Stress separation is usually achieved by solving differential equations of equilibrium after parameter determination from isochromatics and isoclinics.The numerical error resulting from the stress determination is a main concern as it is always a function of parameters in discretization.To improve the accuracy of stress calculation,a novel meshless barycentric rational interpolation collocation method(BRICM)is proposed.The derivatives of the shear stress on the calculation path are determined by using the differential matrix which converts the differential form of the equations of equilibrium into a series of algebraic equations.The advantage of the proposed method is that the auxiliary lines,grids,and error accumulation which are commonly used in traditional shear difference methods(SDMs)are not required.Simulation and experimental results indicate that the proposed meshless method is able to provide high computational accuracy in the full-field stress determination.

Comparative study of various internal fixation methods for treating patellar fractures by three-dimensional photoelasticity

Objective: To compare the biomechanical basis of 3 different internal fixation methods: nitinol patellar concentrator (NT-PC), tension band and wire circle in treating patellar fractures. Methods: The epoxy resin three dimensional photoelasticity patellar models were made by precise moulding, and were fixated by nitinol patellar concentrator (NT-PC), tension band and wire circle respectively. The patellar models with frozen stress stripes were put into the polarized light field and the stress distributions were compared. As for the model fixated by NT-PC, by dividing layer, photographing and tracing, we used the iterative method to calculate the stress value of every internal node of the epoxy resin patellar model, and the character of stress was analyzed. Results: An overall stress field was yielded when the patellar model was fixated by NT-PC, and the stripes were more than that of tension band model and wire circle model, which have only few stress stripes in the fixated layers. Further analysis indicated that there were continuous fixated stresses in the facies articularis and distal pole of patella, and the character of stresses produced by NT-PC were mainly in longitudinal direction, then in transverse direction. The shearing stresses were small. Conclusion: The initiative and continuous memorial stress of NT-PC and its overall stress distribution character are the essence of NT-PC distinguished with tension band and wire circle in treating patellar fractures. The stress character produced by NT-PC is good for the stability of fracture site and prompts fracture healing.

SEPARATION OF PRINCIPAL STRESSES IN DYNAMIC PHOTOELASTICITY

A new and effective method used to separate the transient principal stresses for dynamic photoelasticity is proposed. This is a hybrid method combining the optical method of dynamic caustics and the boundary element numerical method. Firstly, a modified Cranz-Schardin spark camera is used to record simultaneously the isochromatic fringe patterns of photoelasticity and the shadow spot patterns in the dynamic process. By means of the isochromatic fringe patterns, the difference between transient principal stresses in the whole domain and the principal stresses along the free boundary can be solved. In addition, the method of caustics is a very powerful technique for measuring the concentrative load. Then, the sum of the principal stresses is calculated by the boundary integral equation obtained from the Laplace integral transform of the wave equation. So, the transient principal stresses can be determined from the experimental and numerical results. As an example, the transient principal stresses in a polycarbonate disk under an impact load are resolved.

COUPLED VARIATIONAL PRINCIPLES AND GENERALIZED COUPLED VARIATIONAL PRINCIPLES IN PHOTOELASTICITY

In this paper, by applying Lagrange, multiplier method and high order Lagrange multiplier method [1], we systematically derive coupled potential energy principle.coupled complementary energy principle,and generalized coupled potential energy principles and generalized coupled complementary energy principles with two and three kinds of variables in photoelasticity.

Determination of the full-field stress and displacement using photoelasticity and sampling moirémethod in a 3D-printed model

The quantitative characterization of the full-field stress and displacement is significant for analyzing the failure and instability of engineering materials.Various optical measurement techniques such as photoelasticity,moiréand digital image correlation methods have been developed to achieve this goal.However,these methods are difficult to incorporate to determine the stress and displacement fields simultaneously because the tested models must contain particles and grating for displacement measurement;however,these elements will disturb the light passing through the tested models using photoelasticity.In this study,by combining photoelasticity and the sampling moirémethod,we developed a method to determine the stress and displacement fields simultaneously in a three-dimensional(3D)-printed photoelastic model with orthogonal grating.Then,the full-field stress was determined by analyzing 10 photoelastic patterns,and the displacement fields were calculated using the sampling moirémethod.The results indicate that the developed method can simultaneously determine the stress and displacement fields.

基于像素偏振相机的新型光弹技术应用

像素偏振相机与传统光弹方法相结合是近20年来发展起来的一种新型应力测试技术,其克服了传统光弹方法抗环境光干扰能力弱、定量测试操作复杂、很难实现实时测量等缺点。基于此,介绍了该方法的工作原理,并通过2个实例展示了该方法在适应复杂环境及高精度测试方面的巨大技术优势。给出了该新型光弹技术的若干前瞻性应用建议,包括玻璃幕墙安装应力的高效率检测及钢化玻璃内部缺陷的在线检测等。

应用双弹光级联差频调制的红外材料应力缺陷检测

为了实现对Si、Ge、GaAs等红外材料应力缺陷检测,采用两个工作在不同频率的光弹性调制器级联,构成偏振测量系统。应力缺陷引入的双折射延迟量和快轴方位角两个参数,被加载到偏振测量系统调制信号中;利用数字锁相技术同时获取调制信号的基频项和差频项幅值,然后完成两个应力参数求解。详细分析了检测原理,并搭建了实验系统进行验证。实验结果表明,该检测方法及实验系统实现了应力方向角标准偏差为0.31°,应力双折射延迟量标准偏差为0.72 nm,高速、高精度和高重复度的应力缺陷检测,并且实现了Ge样品的应力缺陷方向和值大小分布测量,可为红外材料质量测试分析和评估提供有效手段。

45°双驱动弹光调制高速椭偏测量方法

为解决传统机械旋转补偿器型椭偏仪测量速度较慢问题,提出一种电驱动的双弹光调制的高速椭偏测量方法。通过理论分析并仿真研究45°双驱动弹光调制器工作在纯行波模式下的调制方式。结果发现,当双驱动弹光调制器工作在纯行波模式可实现快轴方向的高速周期性旋转,且相位延迟量为常量。结合椭偏原理,详细研究一种基于双驱动弹光调制的高速椭偏测量理论模型,结果表明,该模型光学周期<10μs,用于实际可真正实现超高速偏光调制。通过研究,有望解决半导体集成电路,微电子和光伏电池等生产过程中薄膜超高速检测难题,对薄膜在线检测、瞬态变化测量具有重要意义和学术价值。

基于弹光调制的椭偏测量驱动电路系统设计

随着椭偏测量技术的发展,对椭偏测量速度、测量范围有了更高的要求。针对传统的双旋转补偿器测量方法受限于机械限制,调制频率低的问题。采用弹光调制技术,利用调制器的快轴旋转取代传统的旋转补偿器,设计了一种基于LC谐振放大的双驱动电路,利用现场可编程门阵列(FPGA)实现对弹光调制器(PEM)的高速驱动控制。根据弹光调制驱动控制要求对电路设计思路和方法进行了详细分析。通过仿真和实验结果表明,所设计的电路系统输出频率能稳定控制在60 kHz,幅值能达到430 VPP以上,满足PEM快轴高速稳定驱动的需求。

弹光调制器动态参数测量与高效驱动匹配研究

为了提高弹光调制器(photoelastic modulator,PEM)的驱动效率,提出了一种基于PEM动态参数测量的阻抗匹配参数计算方法。理论分析了PEM调制幅度与驱动电压大小的关系,建立了PEM及其谐振匹配网络的等效电路模型,在此基础上推导了PEM谐振驱动电压与各个参数的关系,并设计了针对PEM动态测试的测量系统与验证方法。对谐振频率为44.822 kHz的PEM进行各项特性曲线的理论仿真与试验比较,验证了动态测量系统的可靠性,并通过数值仿真得到PEM最优匹配参数。在最优匹配参数附近选取不同匹配参数,测量实际谐振驱动电压,测量结果与仿真曲线相关性达0.996 4,变化趋势在10μF前基本吻合,且在理论最优匹配参数下,实际谐振驱动电压峰值达510 V,优于其他驱动匹配方法,接近理论最大值,相对误差小于1.16%。通过PEM等效动态参数推算的最优匹配参数,可使PEM达到最大驱动效率。

基于光弹法的光纤轴向残余应力检测研究

光纤的残余应力会影响其光学性能和机械特性,文中开展了基于光弹法的光纤轴向残余应力检测研究。建立光纤的光弹模型,利用琼斯矩阵分析光弹图中的光强分布特征,考虑残余应力导致的双折射相位差范围小的特点通过最小光强法进行相位提取,并仿真验证了相位提取算法的准确性,在待测相位不超过±5°条件下理论相位误差小于±0.02°;结合三次样条插值进行相位信息到应力结果的重建,获得的实验结果与商用仪器对比,除商用仪器在部分应力区域存在较大突变外,其余区域二者应力分布特征基本一致。

基于FPGA的光弹调制器驱动控制模块设计

随着技术发展,光学检测对检测范围有了更大的需求,利用光弹调制器取代传统的偏振调制器件,具有着光谱范围广、调制频率高等优势。根据在椭偏测量仪中所应用的光弹调制器结构,设计了一种基于FPGA的光弹调制器控制模块,主要包含驱动模块和反馈调节模块两部分,利用DDS技术和数字锁相技术实现了对光弹调制器的稳定驱动控制。经过测试验证该模块可以稳定产生60kHz及450V_(PP)以上的驱动信号,所设计的驱动模块可以满足光弹调制器的控制需求。

弹光调制器相频特性分析与稳定控制技术

针对弹光调制器(Photoelastic Modulator,PEM)在高压驱动下的谐振频率漂移问题,研究了一种基于PEM谐振相位跟踪的稳定控制技术。建立了PEM与其谐振匹配回路的等效电路模型,推导了PEM驱动电压的幅频、相频关系,以及PEM谐振频率与驱动电压谐振相位的关系。搭建了PEM控制系统,以初始谐振频率的反馈电压相位为零相位基准,调节驱动电压将反馈电压相位稳定在相位基准值附近,并随谐振频率的变化修正相位基准值,从而使驱动电压频率始终稳定于PEM谐振频率附近。以1/4波、半波的PEM的相位延迟幅值为例,分别进行了时长60 min稳定控制测试,实验结果表明:(1)PEM工作在1/4波状态时,相位延迟幅值δ0标准偏差σδq=0.0014 rad,最大相对偏差为0.58%;(2)PEM工作在半波状态时,标准偏差σδh=0.0013 rad,最大相对偏差为0.32%。

100 kHz弹光调制器多功能调制仿真

针对弹光调制器(photoelastic modulator,PEM)在超高速全偏振领域的测量问题,研究一种目标频率在100 kHz附近的圆型PEM,由弹光晶体和2个方位角相差45°的压电驱动器组成。通过理论计算弹光晶体谐振频率和压电驱动器振动频率,当二者频率达到一致时,PEM工作在谐振状态,此时PEM的调制效率达到最高。当PEM达到谐振状态并趋于稳定后,调节两压电驱动器驱动电压的幅值与相位,实现纯驻波模式和纯行波模式两种特殊调制,纯驻波模式可实现纯电控制下调制快轴的延迟量和方位角;纯行波模式可实现纯电控制下调制快轴以PEM谐振频率的半频速度高速旋转。最后,利用COMSOL有限元仿真模拟两种调制模式下PEM,验证两种调制状态下的PEM振型及其快轴方向,表明PEM可实现多功能弹光调制,为后续偏振测量提供理论支撑。

Advancing multi-wavelength photoelasticity through single-exposure detection

In this paper,we present a method to expedite multi-wavelength photoelasticity for efficient stress analysis.By modulating two slightly different-wavelength illumination beams and simultaneously capturing dark-field and bright-field images,our approach acquires four essential polarized images.Spatial filtering of Fourier transforms streamlines inner stress computation,enabling multi-wavelength photoelasticity with a single detector exposure.Theoretical foundations are outlined,and proof-of-principle experiments validate the feasibility with a measurement error below 6.4%.The high measurement speed,determined by the detector’s frame rate,facilitates dynamic sample measurements at video frequency,offering promising advancements in material stress analysis.

煤矿开采激发应力波扰动下逆冲断层失稳机理

【目的】煤矿开采中,人工爆破、顶板垮断等震源激发应力波易诱发断层失稳并导致冲击地压等灾害。【方法】以河南义马矿区F16逆冲断层为研究对象,通过开展断层动光弹实验、数值模拟实验和理论分析,对应力波在断裂结构中的传播规律和应力波作用下断层摩擦能演化特征进行了研究,探讨了震源位置及能量对逆冲断层滑移的扰动规律,阐释了应力波扰动下逆冲断层失稳机理和失稳类型。【结果和结论】研究结果表明:(1)应力波传播会被断层阻隔,并造成断层活化加剧、摩擦能迅速增大。(2)震源应力波能量增大可加强断层自锁效应,当能量超过一定阈值时断层才会解锁。(3)应力波自上至下分区扰动断层并造成断层滑移,其滑移模式受初始应力状态和应力波扰动强度影响。(4)初始高水平静载和强应力波扰动是断层失稳的必要条件。研究成果对断层型灾害防控技术发展具有重要的指导意义。

超高速快轴旋转圆形弹光调制技术研究

针对目前广义椭偏测量速度受限问题,提出利用对称性更优的圆形弹光调制器代替机械旋转补偿器实现超高速测量。对弹光调制器内部受力进行理论研究,得到纯行波模式调制条件并利用COMSOL仿真验证。仿真结果表明,当弹光调制器处于纯行波调制模式时可视为一种快轴方向高速旋转的相位调制器。通过建立阻尼弦振动模型分析不同快轴方向下弹光晶体表面振动位移分布,提出一种弹光调制器在纯行波调制模式下的中心支撑方式用于实验。实验结果表明弹光调制器的快轴以f/2的角速率做圆周运动。同时验证了中心支撑方式可确保弹光调制器谐振后所受阻力均匀且最小,达到最佳支撑效果。研究结果可用于后续广义椭偏测量及各类高速偏振调制领域。

Analysis of the Stress Distribution Pattern of Anatomic and Non-Anatomic Tooth Forms on Maxillary and Mandibular Edentulous Ridges—A Photoelastic Study

Aim: To compare the type of stress distribution pattern occurring with anatomic and non-anatomic tooth forms beneath a complete denture in both maxillary and mandibular arch. Methodology: A photoelastic model of the edentulous maxillary and mandibular ridge was prepared meticulously to simulate the human mandible and maxilla. Two sets of acrylic teeth with anatomic and non-anatomic occlusal forms were used to fabricate upper and lower dentures. A vertical static load of 100 N was applied through the mandibular model to the maxillary model. After load application on the dentures the photoelastic model as well as the upper and lower complete dentures were sectioned in the midline. The sectioned photoelastic model was viewed through a polariscope to observe the fringe pattern indicating varying amounts of stress distribution. In this study, a two-dimensional photoelastic stress analysis technique was utilized. Results: Force per unit area was observed more in anatomic teeth than the non-anatomic counterpart. Hence anatomic tooth forms may increase the possibility of bone resorption rate over a period of time. However, in non-anatomic lower teeth, a decrease in value was observed from posterior to anterior region. Conclusion: Stress of greater magnitude was observed with cuspal teeth whereas non-anatomic (0°) showed slightly less magnitude of stress. Depending upon the clinical situation the clinician needs to choose the type of occlusal tooth forms for edentulous patients.