Experimental crushing behavior and energy absorption of angular gradient honeycomb structures under quasi-static and dynamic compression

The high variability of shock in terrorist attacks poses a threat to people's lives and properties,necessitating the development of more effective protective structures.This study focuses on the angle gradient and proposes four different configurations of concave hexagonal honeycomb structures.The structures'macroscopic deformation behavior,stress-strain relationship,and energy dissipation characteristics are evaluated through quasi-static compression and Hopkinson pressure bar impact experiments.The study reveals that,under varying strain rates,the structures deform starting from the weak layer and exhibit significant interlayer separation.Additionally,interlayer shear slip becomes more pronounced with increasing strain rate.In terms of quasi-static compression,symmetric gradient structures demonstrate superior energy absorption,particularly the symmetric negative gradient structure(SNG-SMS)with a specific energy absorption of 13.77 J/cm~3.For dynamic impact,unidirectional gradient structures exhibit exceptional energy absorption,particularly the unidirectional positive gradient honeycomb structure(UPG-SML)with outstanding mechanical properties.The angle gradient design plays a crucial role in determining the structure's stability and deformation mode during impact.Fewer interlayer separations result in a more pronounced negative Poisson's ratio effect and enhance the structure's energy absorption capacity.These findings provide a foundation for the rational design and selection of seismic protection structures in different strain rate impact environments.

DAMAGE PROGRESSIVE MODEL OF COMPRESSION OFCOMPOSITE LAMINATES AFTER LOW VELOCITY IMPACT

Compressive properties of composite laminates after low velocity impact are one of the most serious circumstances that must be taken into account in damage tolerance design of composite structures. In order to investigate compressive properties of composite laminates after low velocity impact, three dimensional dynamic finite element method (FEM) was used to simulate low-velocity impact damage of 2 kinds of composite laminates firstly. Damage distributions and projective damage areas of the laminates were predicted under two impact energy levels. The analyzed damage after impact was considered to be the initial damage of the laminates under compressive loads. Then three dimensional static FEM was used to simulate the compressive failure process and to calculate residual compressive strengths of the impact damaged laminates. It is achieved to simulate the whole process from initial low-velocity impact damage to final compressive failure of composite laminates. Compared with experimental results, it shows that the numerical predicting results agree with the test results fairly well.

Effect of SACMA and QMW Test Methods on Compressive Properties of Composite Laminates after Low Velocity Impact

Experimental studies on the compressive behavior of composite laminates after low velocity impact was carried out with two test methods.One is SACMA Standard,and the other is a small dimensional specimen test method.Impact damage distributions,compressive failure process after impact,quasi static indentation and compression of laminates with a hole were brought into comparison between these two test methods.The results showed that there is a great difference between these two test methods.Compressive behavior of laminates after impact varies with different test methods.Residual compressive strength of laminates after low velocity impact measured with SACMA Standard can reflect stiffness properties of composite resins more wholely than that measured with the other method can do.Small dimensional specimen test method should be improved on as an experimental standard of compressive strength after impact.

STATIC AND FATIGUE BEHAVIOR OF IMPACTED AS4/PEEK THERMOPLASTIC COMPOSITES UNDER COMPRESSION LOAD

Static and fatigue tests under compression load were made on impacted AS4/PEEK and T300/913C graphite/epoxy with [45/90/-45/0]5S stacking sequence. The comparison of the damage tolerance assessment for thermosetting and thermoplastic composites shows that thermoplastics are more damage tolerant under compression. Impacted thermoplastic composites have excellent compression-compression fatigue behavior. The damage growth life is only a few percent of their total fatigue life and no regular damage growth can be found. Some design principles for thermosetting composite structures may still be used.

Low-Velocity Impact and Compression after Impact(CAI)Behaviors of Carbon-Aramid/Epoxy Hybrid Braided Composite Laminates

Low-velocity impact and in-plane axial compression after impact(CAI)behaviors of carbon-aramid/epoxy hybrid braided composite laminates were investigated experimentally.The following three different types of carbon-aramid/epoxy hybrid braided composite laminates were produced and tested:(a)inter-hybrid laminates,(b)sandwich-like inter-hybrid laminates,and(c)unsymmetric-hybrid laminates.At the same time,carbon/epoxy braided composite laminates were used for comparisons.Impact properties and impact resistance were studied.Internal damages and damage mechanisms of laminates were detected by ultrasonic C-scan and B-scan methods.The results show that the ductility index(DI)values of three kinds of hybrid laminates aforementioned are 37%,4%and 120%higher than those of carbon/epoxy laminates,respectively.The peak load of inter-hybrid laminates is higher than that of sandwich-like inter-hybrid laminates and unsymmetric-hybrid laminates.The average damage area and dent depths of inter-hybrid laminates are 64%and 69%smaller than those of carbon/epoxy laminates.Those results show that carbon-aramid/epoxy hybrid braided composite laminates could significantly improve the impact properties and toughness of non-hybrid braided composite laminates.

Experimental Investigation on Low-Velocity Impact Response and Residual Compressive Bearing Capacity of Composite Stringers

Three types of composite stringers were impacted from two different directions.Relationships between impact energy and visible defect length were found.The critical impact energy corresponding to barely visible impact damage(BVID)of each stringer was determined.Specimens with BVID were then compressed to obtain the residual strength.Experimental results showed that for all types of stringers,the critical energy of in-plane impact is always much lower than out-plane ones.In-plane impact causes much more decrement of stringers'bearing capacity than outplane impact.For both impact directions,I-stringers own the highest defect detectability,T-stringers come second.Meanwhile,I-stringers own the better residual strength ratio than I-stringers and I-stringers.Synthetic considering impact defect detectability and residual bearing capacity after impact,T-stringers own the best compression-afterimpact(CAI)behaviors.

The Impact Compression Behaviors of Silica Nanoparticles—Epoxy Composites

The compressive properties of epoxy with different silica nanoparticles (SiO2 nanoparticles) contents at quasi-static and high strain rates loading were investigated via experiment. This article evaluates the compressive failure behaviors and modes at different SiO2 nanoparticles contents and different strain rates. The results indicated that the stress strain curves were sensitive to strain rate, and the compressive failure stress of composites with various SiO2 nanoparticles contents increased with the strain rates, and it increased along with SiO2 nanoparticles contents and then declined. The compressive failure stress and the compressive failure modes of the composites were apparently different from the change of SiO2 nanoparticles contents.

A Numerical Study on the Water Impact of the Rigid/Elastic Box-Like Structure

Recent damages to the box-like structures caused by wave slamming have made it necessary to study the impact problems of this kind of structure. This paper showed findings from numerical simulations of the rigid/elastic structures, aiming to gain insights into the characteristics of the problem. The results of the rigid cases showed the significance of air compressibility during the impact process, while the slamming phenomena became quite different without the effect. In the elastic cases, the trapped air made the structure vibrate at frequencies much smaller than its eigenfrequencies. Besides, the structural deformation made it easy for the trapped air to escape outwards, which weakened the air cushioning effect, especially at high impact velocities. The above analysis gives the results when the structural symmetry axis was vertical to the water(vertical impacts). In addition, the results were given when the axis was oblique to the water(oblique impacts). Compared with the vertical cases, the impact phenomena and structural response showed asymmetry. This work used the computational fluid dynamics(CFD) method to describe fluid motion and the finite element method(FEM) for the deformable structure. A two-way coupling approach was used to deal with the fluid-structure interaction in the elastic cases.

Drop weight impact analysis of GFRP tubes with hollow glass particle-filled matrix

Protecting occupants or payloads in crashes and blasts is of utmost importance in both moving and immobile structures.One way of achieving this is by using a sacrificial energy absorber.Composite tubes have been studied as potential energy absorbers due to their ability to fail progressively under axial compression.In this study,the energy absorption capability of these tubes is enhanced by adding hollow glass particles to the matrix.Drop-weight tests are performed on composite tubes,and a digital image correlation(DIC)-based technique is used to capture their load-displacement behaviour.This eliminates the use of electronic data acquisition systems,load cells,and accelerometers.The load-displacement curves of the tubes are obtained from the DIC-based technique and examined to understand their crushing behaviour.Although the mean crush load shows a drop,an increase in crush length is noticed.The specific energy absorbed by the tubes improves with an increase in GMB volume fraction.The addition of 0.1,0.2,0.3 and 0.4 vol fractions of GMB results in the specific energy absorption increasing by6.6%,14.7%,24%and 36.6%,respectively,compared to neat glass fibre-epoxy tubes.Visual examination of the tubes and comparison with tubes subject to quasi-static compression is also performed.

含硫酸盐废水对磷石膏胶结充填体材料性能的影响

鉴于矿山废水处理工艺具有一定的局限性,且磷石膏充填工艺需要消耗大量的水资源,将矿山含硫酸盐废水作为磷石膏充填用水并探讨其可行性。结果表明:废水中的硫酸盐能够促进磷石膏充填体的早期水化反应,进而提升充填体早期强度。当SO_(4)^(2-)浓度从0增加至30 000 mg/L时,充填体7 d强度由0.46 MPa升高至0.63 MPa,提高了37%;14 d强度由0.64 MPa升高至1.03 MPa,提高了61%。这主要跟水化产物钙矾石(AFt)和水化硅酸钙(C-S-H)的形成有关;但随着养护时间的增长,充填体28,60,90 d强度均在硫酸盐浓度为15 000 mg/L时达到最高。过量的SO_(4)^(2-)会干扰水化硬化过程,充填体后期强度因受到钙矾石的膨胀特性以及Na2SO4重结晶等影响而出现下降。研究结果可为矿山废水治理和磷石膏充填工艺优化提供新思路。

热冲击高强钢焊接接头的低周疲劳及断裂机理研究

为了研究热冲击下高强钢焊接接头的低周疲劳性能及断裂机理,用电弧焊焊接Q345结构钢,分别在-20~400℃、-40~650℃、-60~900℃下对焊接接头进行循环冲击,用疲劳试验机加载低周疲劳载荷,分析热冲击温度对低周疲劳性能及疲劳强度的影响,并用扫描电子显微镜等分析焊接接头的断裂机理。结果表明:相同疲劳加载次数下,焊接接头的总应变幅值随热冲击循环次数的增加匀速下降;相同热冲击循环次数下,疲劳加载次数越多,焊接接头的应变幅值越小;相同疲劳加载次数和相同热冲击循环次数下,随冲击温度范围的扩大,焊接接头的总应变幅值逐渐减小,但总应变幅值整体变化与冲击温度范围正相关。

玄武岩纤维增强混凝土动态压缩力学性能研究

采用直径为50 mm的分离式Hopkinson压杆试验装置,对不同气压下玄武岩纤维掺量为0%、0.05%、0.1%、0.15%、0.2%的玄武岩纤维增强混凝土(BFRC)进行动态压缩试验,研究BFRC在不同应变率下的力学性能,分析动态抗压强度与准静态抗压强度之间的关系以及冲击韧性,建立BFRC动态本构模型。结果表明:BFRC具有显著的应变率效应;动态抗压强度和比能量吸收值随玄武岩纤维掺量的增加呈先增加后减小的趋势,掺量为0.1%时达到最大值;动态强度增长因子与应变率对数近似呈线性增长关系;BFRC动态本构模型拟合试验与应力-应变曲线结果较吻合。

基于率相关改进桥联模型的CFRP材料动态力学性能研究

桥联模型在预测CFRP材料静态力学性能上具有较高的精度,但目前鲜有基于桥联模型描述CFRP材料动态力学性能的报道。基于此,采用考虑应变率效应的本构方程与强度准则改进桥联模型。利用文献实验数据对改进后的模型进行了确认,针对侵彻弹使用环境,设计制备了CFRP层合结构并进行SHPB动态实验。理论预估模量与实验结果基本一致,理论强度值高于实验值约7%,由此校验了相关改进桥联模型在动载环境下的适用性。结合课题组已有的CFRP壳体侵彻试验结果,进一步验证了该理论模型可用于CFRP材料在冲击载荷下的性能预测。进一步的试验结果细观分析和数值模拟研究表明,X方向试样的动态破坏模式以层间分层为主,而Y方向则以纤维的压缩破坏与基体的剪切破坏为主。为CFRP材料用于抗冲击等动态载荷下的力学行为预测提供了一种可行的分析手段。

泡沫铝基耗能装置在铁路桥墩防车撞中的应用研究

随着公路、铁路、城市立交桥的大量建设,跨线桥数量剧增,桥墩被汽车撞击的可能性大大增加。因此,针对目前铁路桥墩防车撞防护装置的不足,提出了一款泡沫铝基组合耗能装置的结构型式。该研究结合了静力压缩试验、落锤冲击试验以及有限元数值模拟,研究了防撞装置缓冲材料的物理力学性能及车辆撞击防撞装置的冲击动力学响应。结果表明,泡沫铝-聚氨酯-泡沫铝三层组合结构型式中工况3~4吸能效果最佳,其吸能密度(EA)、比吸能(SEA)以及吸能效率(EEA)值分别为3×10^(3) kJ/m^(3)、12.21 kJ/kg、28.57%。在数值模拟中,无防撞装置工况下,车辆撞击力最大值为5 332.99 kN,桥墩吸收的能量为22.05 kJ,最大应力为124.46 MPa,墩身产生明显损伤;在有防撞装置工况下,车辆撞击力最大值为2 674.41 kN,降低了49.85%;桥墩最大应力为6.96 MPa,降低了94.41%。结果表明该防撞装置组合结构对桥墩起到了良好的防护效果。

复合材料蜂窝夹芯结构低速冲击后压缩强度的可靠性与灵敏度分析

建立了一种复合材料蜂窝夹芯结构低速冲击后压缩强度的可靠性与灵敏度分析方法。利用ABAQUS有限元分析软件和VUMAT子程序建立了蜂窝夹芯结构冲击后压缩渐进损伤失效分析模型,并通过试验验证模型的有效性;在此基础上,利用Python语言对模型中材料力学性能和面板厚度、蜂窝芯子厚度进行参数化;采用径向基神经网络代理模型替代渐进损伤失效分析模型;基于蒙特卡洛法进行冲击后压缩强度的可靠性分析;分别采用基于方差和基于失效概率的方法进行参数的灵敏度分析,并研究参数的变异系数对结构可靠性的影响。结果表明:在外载荷低于10000 N,结构失效概率小于0.00017的情况下,当外载荷达到12700 N时,结构失效概率达到0.9;面板的力学性能、面板厚度、蜂窝芯厚度对冲击后压缩强度的影响较大;冲击后压缩强度的变异系数随着参数变异系数的增大而增大。

玄武岩纤维对混凝土力学性能影响试验研究

为解决普通水工混凝土力学性能不足的问题,采用单丝长度12 mm的玄武岩纤维为原料,研究了玄武岩纤维掺量对混凝土抗压、抗拉、抗渗及抗冲磨4个性能的影响,并分析其影响机理。结果表明,随着玄武岩纤维掺量的增加,混凝土抗压强度一定程度降低,劈裂抗拉强度先减小后增加,体积掺量为0.3%时劈裂抗拉强度可提高3%。混凝土中掺入0.1%、0.2%的玄武岩纤维,抗渗性能分别提高14%、29%。在常规混凝土中掺入玄武岩纤维后会显著降低抗冲磨强度。研究成果可为不同应用场景下水工混凝土的配合比优化设计提供参考和借鉴。

平纹编织复合材料加筋壁板低速冲击及冲击后压缩性能多尺度分析

该文通过构建平纹编织复合材料(plain woven composites,PWC)的微/细/宏观多尺度模型,对复合材料T型和工型加筋壁板的低速冲击(low-velocity impact,LVI)和冲击后压缩(compression after impact,CAI)性能进行分析。根据PWC内部结构特征,构建微观和细观代表性体积单元(representative volume element,RVE)模型,通过施加不同的载荷条件,预测其等效力学参数。同时,基于局部均匀化方法,将细观RVE模型转化为包含0°和90°子胞的等效交叉层合板(equivalent cross-ply laminate,ECPL)胞元。通过ECPL胞元建立PWC加筋壁板的宏观分析模型,并进行LVI和CAI性能分析。首先进行了能量为8 J、10 J和12 J的LVI试验和多尺度模拟,研究了PWC加筋壁板在LVI载荷下的力学行为。随后,对不同能量冲击后的加筋壁板进行CAI试验和数值模拟,研究其冲击后压缩剩余力学性能和损伤行为。最后,通过对比分析不同能量冲击下的LVI和CAI试验和预测结果,发现多尺度模型对加筋壁板力学性能的预测误差均小于6%,验证了该多尺度模型的有效性。试验和预测结果表明,在CAI载荷作用下,PWC加筋壁板的蒙皮部分沿着冲击损伤的位置发生完全断裂,其中,纤维断裂和层间分层成为PWC加筋壁板的主要损伤形式。此外,工型加筋壁板表现出更好的抵抗压缩强度衰减能力。

PVC泡沫夹芯板单点低速冲击动态响应与冲击后剩余抗压强度试验研究

[目的]为了研究复合材料夹芯板抗冲击力学性能,选取尺寸为150 mm×100 mm×26 mm的正交编织玻纤复合材料PVC泡沫夹芯板为研究对象,研究其单点低速冲击动态响应与冲击后的剩余压缩强度。[方法]开展一系列不同冲击能量下夹芯板落锤冲击试验,研究夹芯板在不同冲击能量下的失效模式、冲击力–位移响应和能量吸收特性。随后开展含冲击损伤的夹芯板试样准静态压缩试验,分析含冲击损伤的复合夹芯板的最大压缩承载能力和剩余压缩强度。[结果]研究结果发现,不同冲击能量下夹芯板失效模式和冲击力–位移特性有明显的区别,芯层主要通过压缩变形来吸收冲击能量。随着冲击能量增大,复合材料夹芯板的最大冲击力、凹坑深度和结构吸收能量都随之增大,夹芯板结构的最大压缩承载能力和剩余压缩强度在逐渐降低,夹芯结构受冲击面板的损伤程度决定了夹芯板的剩余压缩强度。[结论]研究工作可为舰船结构抗冲击设计提供参考。

高校实验室自制气体燃烧装置风险防控研究

高校实验室自制气体燃烧装置存在较高风险。首先介绍了计算可燃混合气爆炸极限、绘制燃烧三元相图两种方法,用于判断常压室温条件下混合气体燃爆特性。然后以常压燃烧器和爆燃/爆轰装置为例研究爆炸风险,分析了装置冲击部位异常温升的关键因素,给出了负压状态下预混可燃气发生绝热压缩导致爆炸的计算实例。最后,基于本质安全,从实验方案安全技术要点、实验装置设计制造安全要求、实验室环境安全提升、个人防护用品配置四方面提出爆炸防控措施。

SHPB循环冲击实验技术在岩石冲击动力学教学中的应用研究

该文通过将SHPB实验与岩石冲击动力学相关理论课程相结合的教学模式,提高学生对岩石冲击力学响应和能量演化特征的认知与理解,培养学生在科学实验方面的实际操作能力和严谨态度,发挥学生自主开展实验研究的主观能动性,提升教学效果。基于多学科交叉融合理念,联系科学研究热点问题,引导学生进一步思考并探索更多“SHPB+”,有助于培养学生的科研实践能力与思维创新精神。