BFRP筋增强海水海砂混凝土梁的抗冲击性能EI北大核心CSCD

为研究玄武岩纤维增强复合材料(basalt fiber reinforced polymer,BFRP)筋增强海水海砂混凝土(seawater sea-sand concrete,SSC)梁的抗冲击性能,利用落锤冲击装置研究了不同冲击能量(1818 J,2727 J,3636 J,4848 J)作用下,不同混凝土强度(30 MPa,50 MPa)和配筋率(0.23%,0.48%)的BSFP-SSC梁冲击响应,并测试了冲击后梁的残余承载力。结果表明,随着冲击能量的增加,BFRP-SSC梁的破坏模式由弯曲破坏转变为剪切破坏,梁的残余承载力系数逐渐降低。提高配筋率或海水海砂混凝土强度,均可有效降低梁的最大跨中位移,提升初始峰值冲击力和抗冲击性能。该研究可为BFRP筋增强海水海砂混凝土梁的抗冲击设计提供重要依据。     

冲击位置对复合材料加筋板冲击后压缩行为影响试验

对低速冲击(LVI)载荷下不同冲击位置对T型复合材料加筋板损伤容限的影响进行了试验研究.选取了2个典型冲击位置,即:两筋间蒙皮和筋条长桁边缘,引入目视可检冲击损伤(VID).借助目视及无损检测手段观察到不同冲击位置处的损伤存在显著差异.相比于蒙皮冲击,长桁边缘冲击处的损伤形式更复杂,表现为:纤维断裂、基体开裂、分层、层...     

温度老化对GFRP/BFRP筋残余弯曲性能的影响

对玻璃/玄武岩纤维增强复合材料(GFRP/BFRP)筋材在温度老化作用后的弯曲性能进行了试验研究,重点探讨了不同作用温度及恒温时间对不同直径的两类FRP筋材的弯曲性能影响特性,同时采用扫描电子显微镜(SEM)对温度老化作用后部分GFRP/BFRP筋的微观结构变化及损伤机理进行了分析.试验与分析结果表明:(1)温度老化作用后GFRP/BFRP筋材弯曲强度与最大应变随作用温度升高均呈阶段性下降的趋势,而弯曲弹性模量无明显退化,其保留率均在90％以上;(2)温度老化作用后直径较大的GFRP筋材的弯曲性能退化更为明显;且G12筋的弯曲性能保留率退化曲线均高于B12筋,说明BFRP筋的弯曲性能对温度作用更为敏感;(3)在270℃高温环境下,GFRP/BFRP筋弯曲性能随着恒温时间的延长均呈现线性下降趋势;(4)结合试验结果和SEM微观结构分析,可认为造成温度老化作用后两类FRP筋弯曲强度退化的主要原因是纤维与树脂基体间协同工作效果和纤维-树脂基体界面性能的显著降低.最后,结合本试验结果,给出了500℃以内温度老化作用后GFRP/BFRP筋材弯曲强度退化的计算模型以及线性插值预测方法,便于实际工程应用.     

中低加载速率下BFRP筋-混凝土粘结性能研究

BFRP(basalt fiber reinforced polymer)筋是一种取代钢筋用于土木工程领域的新型纤维复合材料,中低加载速率下BFRP筋-混凝土粘结性能是保证其协同作用承受动荷载的重要前提。该文根据正交试验方法设计了16组粘结试件,利用MTS试验系统对不同加载速率(0.005 mm/s~5 mm/s)下的BFRP筋-混凝土试件进行了中心拉拔试验,研究了加载速率、混凝土强度及BFRP筋直径等因素对粘结性能的影响。在现有粘结强度计算模型的基础上,对粘结特征参数进行了修正,提出了中低加载速率下的BFRP筋-混凝土动态粘结强度计算公式,进一步建立了BFRP筋-混凝土粘结滑移本构关系模型。结果表明:BFRP筋-混凝土粘结试件主要发生拔出破坏与劈裂破坏,粘结滑移过程可分为滑移段、下降段和残余段;粘结强度随加载速率和混凝土强度的增大而增大,而随纤维筋直径的增大却显著减小;理论计算结果与试验结果吻合良好,为预测中低加载速率下BFRP筋-混凝土粘结性能提供了一种有效手段。     

整体中空复合材料低速冲击响应研究

整体中空复合材料是一种新型的结构、功能材料,具有优异的力学性能与可设计性.本工作选取两种不同芯层高度的复合材料进行低速冲击相关实验研究:5mm材料进行不同级别能量的低速冲击实验,7mm材料进行铝蒙皮前后低速冲击对比实验.借助ORIGIN软件对材料低速冲击过程中的主要参数(速度、位移、冲击载荷、吸收能量等)进行了详细分析.结果表明:低速冲击过程中的初始损伤能量可用来表征材料的破坏程度;铝蒙皮有利于增强材料的抗低速冲击性能.     

BFRP筋混凝土深梁动态剪切破坏尺寸效应模拟EI北大核心CSCD

为研究玄武岩纤维增强聚合物(BFRP)筋混凝土深梁动态剪切破坏机制及其尺寸效应规律,考虑混凝土非均质性、混凝土/BFRP筋相互作用以及混凝土和BFRP筋在材料层面的应变率效应,建立了BFRP筋混凝土深梁细观尺度三维数值模型。利用已有的试验数据验证了该数值模拟方法的合理性和准确性,采用该方法研究了不同尺寸但几何相似的BFRP筋混凝土深梁在不同应变率下的剪切破坏模式及失效机制。分析了截面尺寸、配箍率、应变率对BFRP筋混凝土深梁剪切破坏及相应尺寸效应规律的影响。结果表明:动载下梁的破坏模式与静载时存在较大差异,但均表现出尺寸效应;增大应变率及配箍率均能有效提高梁承载力且削弱剪切尺寸效应,但应变率的作用程度明显大于配箍率。     

复合材料加筋板低速冲击损伤及剩余压缩强度试验研究

采用落锤法对复合材料加筋板进行了低速冲击损伤（LVI）试验,根据复合材料加筋板构型,设计了冲击支持支架,研究了支持支架的间距对冲击结果的影响;用相同的冲击能量对复合材料加筋板结构中3处典型位置进行冲击,得到不同位置的损伤形貌;分别对完好件和损伤试验件进行压缩试验,将试验结果进行对比,分析不同位置的冲击损伤对结构压缩性能的影响。试验结果表明：在相同的冲击能量下,支持支架间距越小,所造成的冲击损伤越严重;在50 J冲击能量下,筋条区蒙皮处的冲击所造成的损伤不易观察,筋条间蒙皮处的冲击所造成的损伤最为明显,而筋条边缘蒙皮处的冲击可以导致筋条边缘的脱粘;冲击损伤会使加筋板屈曲载荷轻微下降,筋条间蒙皮和筋条区蒙皮冲击损伤对压缩结果影响相对较小,筋条边缘处的冲击会引起损伤处蒙皮的子层屈曲,并影响结构破坏形式,使结构压缩承载能力有较为明显的下降。     

BFRP筋与珊瑚混凝土粘结性能试验研究

为研究玄武岩纤维增强复合材料筋(BFRP筋)与珊瑚混凝土的粘结性能,对不同直径(d=8 mm、12 mm)、不同粘结长度(2.5 d、5.0 d与7.5 d)及不同养护环境(标准养护室养护、20±2℃人工海水养护)的共24个BFRP筋与珊瑚混凝土粘结锚固试件进行了中心拉拔试验。结果表明:除直径为12 mm,粘结长度为7.5 d的拉拔试件出现珊瑚混凝土劈裂破坏外,其余试件均为BFRP筋从珊瑚混凝土中拔出破坏,其破坏形态与BFRP筋和普通混凝土粘结破坏形态无明显区别,只是更易发生劈裂破坏。其粘结滑移曲线可分为微滑移阶段、滑移阶段、剥离阶段、下降阶段和残余阶段共5个阶段。其最大平均粘结应力随直径与粘结长度的增加显著减小。标准养护条件下的BFRP筋与珊瑚混凝土的粘结强度明显高于20±2℃人工海水养护下的粘结强度。     

BFRP筋钢-混组合梁高温后力学性能试验

设计了常温(25℃)、200℃、400℃和600℃四个工况，通过模型试验方法探究了玄武岩纤维增强树脂复合材料(Basalt fiber reinforced polymer,BFRP)筋钢-混组合梁高温后的破坏形态和力学性能。通过分析试验梁裂缝开展、挠度变形、温度场和破坏过程规律，研究BFRP筋和普通钢筋钢-混组合梁的破坏模式和承载能力。结果表明：经历400℃高温后，BFRP筋劣化导致力学性能大幅降低；筋体膨胀导致混凝土板开裂，其裂缝开展与普通钢筋钢-混组合梁显著不同，主裂缝沿横向筋材规律开展，且裂缝较宽。温度低于400℃时，由于混凝土的包裹，BFRP筋未达到劣化温度，两种钢-混组合梁承载能力和外观差别较小；600℃后，BFRP筋劣化，削弱了混凝土板刚度和强度，导致BFRP筋钢-混组合梁承载能力比普通钢筋钢-混组合梁降低更多；BFRP筋钢-混组合梁因整体刚度较小，加载后变形更大。高温后两种钢-混组合梁破坏模式相似，均为剪切破坏，有明显弹性、弹塑性和破坏阶段；600℃时，两种钢-混组合梁延性大幅降低，塑性变形减少，破坏较为突然。研究成果可为BFRP筋在钢-混组合梁中的应用提供参考。     

SMA杂交复合材料板低速冲击响应研究

本应用有限单元法，研究了形状记忆合金(SMA)对复合材料板低速冲击响应性能的影响。研究中，通过分析对比不同SMA体积含量复合材料板的低速冲击响应，得出SMA能的效地改善复合材料板低速冲击响应性能的结论，其中，SMA体积含量为0．3的复合材料板的最大挠度大约减少了30％。     

K8型单层球面网壳顶点竖向冲击下的冲击荷载特征及荷载简化模型

为简化网壳结构遭受冲击作用时复杂的接触分析过程,基于ANSYS/LS-DYNA建立了单层K8型球面网壳模型,并模拟其在不同冲击作用下的失效过程,辨别网壳的失效模式,并获取了冲击过程中的冲击力曲线。通过对网壳遭受竖向冲击荷载下的这些冲击力曲线特征进行分析,提出了简化的冲击荷载模型,并应用能量守恒定律和动量定理确定了模型相关参数。利用此冲击力模型对网壳结构在冲击荷载下的响应进行分析并与实体冲击物作用下的响应进行了对比,验证了该模型的准确性,应用该模型可以实现对网壳抗冲击性能的简单有效评估。     

缝合复合材料层板低速冲击及冲击后压缩实验研究

通过对缝合复合材料层板进行低速冲击和冲击后压缩实验, 研究了不同类型的缝合复合材料层板的冲击损伤特性及冲击后压缩的剩余强度。实验研究表明: 基体损伤和分层是缝合层板与未缝合层板低速冲击的主要损伤模式, 缝合层板具有更好的抗冲击性能, 更高的冲击后压缩强度。缝合密度越大的层板其抗冲击性能越好, 冲击后压缩强度越高。缝合方向为0°的缝合层板较缝合方向为90°的缝合层板具有更好的抗冲击性能和更高的冲击后压缩强度。增加0°方向铺层, 减少45°、-45°方向铺层, 可以提高缝合层板的抗冲击性能和冲击后压缩强度。     

Hypervelocity impact testing of pressure vessels to simulate spacecraft failure

A series of hypervelocity impact tests are conducted against thin-walled aluminum pressure vessels to investigate failure mechanisms. The vessels, 0.05 and 0.08 inches thick, are constructed to replicate the material properties of the International Space Station (ISS). The vessels are pressurized to simulate the conditions experienced by the habitable modules of the ISS. A test matrix incorporating shielded thin plates, shielded vessels under no pressure and shielded vessels under internal pressure is developed to take advantage of knowledge gained in earlier tests. Given the design parameters of the ISS coupled with the capabilities of light gas gun testing, it is shown that a catastrophic failure due to unzipping is unlikely.     

Capacity building for trade impact assessment: lessons from the development of environmental impact assessment

This paper examines difficulties in creating capacity to undertake impact assessments of trade policy and possible approaches to overcoming them, particularly in developing countries. The assessment of trade agreements and related policies can be a highly complex task, involving many different specialist disciplines. Also, many hurdles have to be overcome to integrate an effective impact assessment process into policy- formulation and decision-making mechanisms. Difficulties in some ways similar, in other ways different, have been encountered in developing effective environmental impact assessment (EIA) systems. This paper reviews experience with EIA capacity-building, and considers how the lessons learned might be applied to initiatives to build capacity for the impact assessment of trade policy.     

Characterization of fracture modes in stitched and unstitched cross-ply laminates subjected to low-velocity impact and compression after impact loading

The insertion of transverse reinforcing threads by stitching is a very promising technique to restrict impact damage growth and to improve post-impact residual strength of laminates. In order to develop general models capable of addressing the issues of impact resistance and damage tolerance of stitched laminates, detailed understanding of the nature and extent of damage, identification of the dominant fracture modes and assessment of the effect of stitches on the damage development are essential. In this study, both instrumented drop-weight tests and compression-after-impact tests were carried out to examine and compare the damage responses of stitched and unstitched graphite/epoxy laminates subjected to low-velocity impact. The progression of damage and its effect on post-impact performance was investigated in detail in two classes of cross ply laminates ([0₃/90₃]_s and [0/90]_3s) by means of an extensive series of damage observations, conducted with various complementary techniques (X-radiography, ultrasonics, optical microscopy, deply). The results of the analyses carried out during the study to characterize the key fracture modes and to clarify their relationship with the structural performance of both stitched and unstitched laminates are reported and discussed in the paper.     

Numerical simulations of low-velocity impact on an aircraft sandwich panel

The potential hazards resulting from a low-velocity impact (bird-strike, tool drop, runway debris, etc.) on aircraft structures, such as engine nacelle or a leading edge, has been a long-term concern to the aircraft industry. Certification authorities require that exposed aircraft components must be tested to prove their capability to withstand low-velocity impact without suffering critical damage.

This paper describes the results from experimental and numerical simulation studies on the impact and penetration damage of a sandwich panel by a solid, round-shaped impactor. The main aim was to prove that a correct mathematical model can yield significant information for the designer to understand the mechanism involved in the low-velocity impact event, prior to conducting tests, and therefore to design an impact-resistant aircraft structure.

Part of this work presented is focused on the recent progress on the materials modelling and numerical simulation of low-velocity impact response onto a composite aircraft sandwich panel. It is based on the application of explicit finite element (FE) analysis codes to study aircraft sandwich structures behaviour under low-velocity impact conditions. Good agreement was obtained between numerical and experimental results, in particular, the numerical simulation was able to predict impact damage and impact energy absorbed by the structure.     

Characterizing secondary debris impact ejecta

All spacecraft in low earth orbit are subject to high-speed impacts by meteoroids and orbital debris particles. These impacts can damage flight-critical systems, which can in turn lead to catastrophic failure of the spacecraft. In addition to threatening the operation of the spacecraft itself, on-orbit impacts also generate a significant amount of damaging ricochet ejecta particles. These high-speed particles can destroy critical external spacecraft subsystems, which also poses a threat to the spacecraft and its inhabitants. Since the majority of on-orbit debris impacts are expected to occur at oblique angles, the characterization of ricochet debris created in an orbital debris particle impact is an issue that must be addressed. This paper presents the results of a study performed to develop an empirical model that characterizes the secondary ejecta created by a high speed impact on a typical aerospace structural surface. Specifically, the model predicts the spread and trajectory of ricochet debris particles created in a hypervelocity impact as well as the size an velocity of the most damage particle in the ricochet debris cloud. Results obtained using the model are compared with experimental results and predictions obtained in a previous study.     

‘International Journal for Numerical Methods in Engineering’ keeps first place in impact factor ranking for 2008 with historic high impact factor of 2.229

The International Journal for Numerical Methods in Engineering keeps its first place in impact factor ranking for 2008 with the historic high impact factor of 2.229, as announced in the 2008 Journal Citation Reports^® (Thomson Reuters, 2009). Copyright © 2009 John Wiley & Sons, Ltd.     

直线交变冲击机构磁电式速度传感装置分析

针对直线交变冲击机构高频、高速、难以检测的特点,提出了基于电磁感应原理的检测方法,完成了对直线交变冲击机构的冲击特性检测。基于ANSYS Maxwell软件建立了检测系统电磁场仿真模型。通过仿真计算与试验结果的对比分析,验证了电磁感应检测方法的可行性以及电磁仿真模型的正确性。进一步,分析了气缸材料、线圈匝数、线圈柱面径向位置等不同参数对磁电式速度传感装置性能的影响。研究结论为方便、准确地测量气驱直线交变冲击机构冲击特性参数提供了有效依据。     

低速冲击下复合材料层板压缩许用值

为评估航空结构中常用的T300级和T800级2种碳纤维/环氧树脂复合材料层压板的冲击后压缩许用值,对2种材料体系下具有不同厚度及铺层的层板进行了低速冲击和冲击后压缩试验;讨论了冲击能量、凹坑深度、损伤面积及冲击后剩余压缩强度等之间的关系,以及厚度、铺层、表面防护等因素对其造成的影响;重点关注了2种材料体系下各组层板的目视勉强可见冲击损伤(BVID)形成条件以及含BVID层板的剩余强度.结果表明:厚度及铺层对层板的凹坑深度-冲击能量关系影响较大,而对冲击后压缩强度-凹坑深度及冲击后压缩破坏应变-凹坑深度关系影响较小,且在相同铺层比例下,BVID对应的冲击能量随厚度近似呈线性增长.X850层板的损伤阻抗性能明显优于CCF300/5228层板的,但二者损伤容限性能相当.加铜网、涂漆等表面处理显著提高了层板的损伤阻抗,但对损伤容限性能影响不大;在损伤不超过BVID时,所有CCF300/5228试件的压缩破坏应变均大于4 000 με,而X850材料体系下压缩破坏应变均在3 000 με之上.