编织角和承载方向对三维四向编织复合材料动态压缩性能的影响

利用分离式霍普金森压杆（SHPB）装置对三维四向编织碳纤维增强树脂基复合材料的动态压缩性能进行了研究。通过对编织角为20°、30°和45°的试验件分别进行沿纵向、横向和厚度方向的动态压缩试验,得到材料在800~2 000/s应变率范围内的应力-应变曲线,并与准静态压缩试验结果进行对比,研究了应变率、压缩方向及编织角对材料极限强度和弹性模量的影响。结合高速摄影记录的动态压缩过程,进一步分析了不同情况下材料的破坏模式与破坏过程。结果表明：应变率越高,材料的极限强度和弹性模量越大,材料在受压的三个方向上均具有一定的应变率强化效应,且高应变率下表现出比准静态压缩时更明显的脆性;编织角的改变对材料在三个方向上的动态压缩性能均有影响,其中对纵向的影响最为明显;不同方向受压时材料的失效形式不同,且准静态和高应变率下的失效形式也有区别。     

动态载荷下C/C复合材料的压缩破坏行为

利用电子万能试验机以及Split Hopkinson Compressive Bar(SHPB)测试了2DC/C复合材料在准静态、动态载荷下的压缩性能,结合光学显微镜分析了其在不同应变率下的破坏形貌、讨论了应变率对压缩破坏形貌的影响。结果表明:与准静态(10-4/s)相比,动态载荷下(5×102/s)复合材料的压缩强度提高了55%,压缩刚度提高了66%,具有较强的应变率效应;在准静态载荷下,C/C复合材料沿40°角剪切破坏,断口上炭纤维破坏具有溃散及剪切破坏特征,而在动态载荷下,C/C复合材料破坏成大小不一的碎片,其炭纤维破坏具有劈裂特征。C/C复合材料破坏模式的不同可归结为基体及界面强度的应变率效应。     

动态压缩下一种碳纤维织物增强复合材料的各向异性力学性能实验研究

为获得一种碳纤维二维正交平纹机织布增强树脂基复合材料准静态和动态压缩力学性能, 对其三个主方向(垂直于碳布方向、碳布经向、碳布纬向) , 分别利用Inst ron 试验机和SHPB 实验技术, 进行了准静态压缩和动态压缩实验。得到了三个主方向从低应变率(10 -3 / s) 到高应变率(约103 / s) 下的压缩应力2应变曲线和压缩强度, 并通过分析得到了三个主方向上的动态压缩响应特点: 垂直于碳布方向的力学性能及其与应变率的相关性主要由树脂基体所控制; 碳布经向和纬向的力学性能主要由碳纤维所控制, 并且和纤维初始微屈曲相关。最后, 分别给出三个主方向上的压缩强度和弹性模量与应变率相关性的表达式。      

一种碳纤维织物增强复合材料的层间冲击拉伸力学性能实验研究

为获得一种碳纤维二维正交平纹机织布增强树脂基复合材料准静态和动态下的层间拉伸力学性能,对垂直于碳布平面方向 ( 横向),分别利用Instron试验机和SHTB实验技术,进行了准静态拉伸和动态拉伸实验。得到了从低应变率 (10-3/s) 到较高应变率 (约3×102/s) 下的拉伸应力-应变曲线和拉伸强度。通过分析发现,拉伸破坏总是发生在相邻铺层的层间界面处,层间拉伸模量和拉伸强度都具有一定的应变率强化效应,但是层间拉伸破坏应变几乎不存在应变率效应。      

C/C复合材料压缩破坏的应变率效应研究

研究了碳布叠层/碳复合材料在四种不同应变率下的压缩性能, 对其在准静态、动态载荷下的压缩破坏机理进行了初步的探讨. 研究结果表明: C/C复合材料的压缩破坏强度具有较强的应变率效应, 与准静态(10^-4/s)相比, 复合材料的动态(1.5×10²/s)压缩强度可提高70%左右; 复合材料在准静态、动态载荷下力学性能的差异可归结为纤维与基体界面特性的应变率效应以及不同应变率下破坏模式的不同.     

三维正交机织复合材料的动态压缩性能

本文作者利用分离式Hopkinson压杆装置对玻璃纤维三维正交机织复合材料进行了高应变率下面外、面内方向的压缩试验,并在万能试验机下进行了相应的准静态压缩。获得3 个高应变率及准静态下的应力-应变曲线,观察了试样的破坏形貌。结果表明：玻纤三维正交机织复合材料是应变率敏感材料,最大应力、压缩模量随着应变率的增大而增大。三维正交结构使复合材料体现出各向异性：面外的最大应力、失效应变比面内大;面内的压缩模量大于面外,且压缩模量对于应变率的变化比面外方向敏感;经纬向相比,纬向的最大应力大于经向。     

三维编织C/SiC复合材料的拉压实验研究

针对三维编织C/SiC复合材料进行了拉伸试验和压缩试验,得到了材料拉伸、压缩的主要力学性能参数、损伤发展情况及破坏规律。从宏观角度比较了在两种载荷下材料弹性性能及强度的区别,得到了一些试验研究结论。结果表明:三维编织C/SiC在拉伸和压缩载荷下的应力-应变曲线有明显的非线性特性;拉伸模量低于压缩模量;拉伸强度高于压缩强度;声发射数据可以用来检测材料内部损伤的发展。      

三维编织复合材料压缩力学性能的实验研究

通过宏观压缩实验,研究了三维四向编织复合材料的抗压力学性能;同时,为了认识其压缩失效机理,对压缩试件的破坏断口进行了扫描电镜分析。实验结果表明:纵向压缩模量比横向压缩模量大得多;影响纵向压缩力学性能的主要参数是材料的编织角,随编织角的变化,复合材料的纵向压缩破坏机理发生了变化,编织角较小时,材料表现为脆性特征;当编织角大于某个角度,材料的应力-应变曲线趋于非线性,延性增加,更多地表现为塑性破坏特征。此外,横向压缩的破坏机理与纵向压缩明显不同。     

UHMWPE/乙烯基酯2.5D角联锁机织复合材料动态压缩性能实验研究

采用分离式霍普金森压杆(SHPB)动态测试系统和岛津材料试验机,对材料厚度方向的压缩性能进行实验研究,得到了三种高应变率(360,710s-1和1120s-1)和准静态下的压缩应力-应变关系,压缩强度和冲击吸能,通过冲击破坏形貌探讨材料的动态压缩破坏模式和吸能机理.结果表明:UHMWPE/乙烯基酯2.5D角联锁机织复合...     

应变率对硫化橡胶压缩力学性能的影响

利用分离式霍普金森压杆(SHPB)和材料实验机MTS810对硫化橡胶进行动态和准静态单轴压缩实验,获得硫化橡胶的应力-应变响应曲线,研究了应变率对其压缩力学性能的影响。实验结果表明,硫化橡胶在低应变率时的应变率效应不明显,然而在较高应变率时,应变率对其动态应力-应变关系有明显的影响,弹性模量、屈服应力以及流动应力都随应变率的增大而增大。采用基于应变能函数理论的橡胶本构模型来描述硫化橡胶压缩荷载下的力学行为。数值模拟了硫化橡胶的应力-应变历程,并与实验数据进行比较,结果显示两者吻合良好。     

High strain rate behavior of 4-step 3D braided composites under compressive failure

The out-of-plane and in-plane compressive failure behavior of 4-step 3D braided composite materials was investigated at quasi-static and high strain rates. The out-of-plane and in-plane direction compressive tests at high strain rates from 800/s to 3,500/s were tested with the split Hopkinson pressure bar (SHPB) technique. The quasi-static compressive tests were conducted on a MTS 810.23 tester and compared with those at high strain rates. The comparisons indicate that the failure stress, failure strain and compressive stiffness both for out-of-plane and in-plane loading directions are rate sensitive. For example, the failure stress, failure strain and stiffness are 55.19 MPa, 6.70% and 1.35 GPa respectively as opposed to 145.00 MPa, 1.21% and 13.50 GPa respectively for strain rate of 2,500 s⁻¹ under in-plane compression. The 3D braided composites have higher values of failure stress and strain for out-of-plane than for in-plane compression at the same strain rate; however, the in-plane compression stiffness is higher than that of out-of-plane compression at high strain rates. The compressive failure mode of 3D braided composites in the out-of-plane direction is mainly shear failure at various strain rates, while for the in-plane direction it is mainly cracking of matrix.     

Investigating the transverse behavior of Glass–Epoxy composites under intermediate strain rates

In this study, the strain rate effects on transverse tensile and compressive properties of unidirectional Glass fiber reinforced polymeric composites are investigated. To demonstrate strain rate effects, the tensile and compressive composite specimens with identical configuration are fabricated and tested to failure in the transverse direction at quasi-static strain rate of approximately 0.001 s⁻¹ and intermediate strain rates of 1–100 s⁻¹. The tensile and compressive tests are performed using a servo-hydraulic testing apparatus equipped with strain rate increasing mechanisms. For performing the practical tests, a jig and a fixture and other test supplies are designed and manufactured. The performance of the test jig is evaluated and showed that it is adequate for composites testing under tension and compression loads. The effects of strain rate on mechanical properties (maximum strength, modulus, and strain to failure) are considered. The characteristic results for the transverse properties indicate that damage evolution is strain-rate-dependent for the examined material. Also, a strain-rate-dependent empirical material model associated with different regression constants is proposed based on the experimental results obtained to characterize the rate dependent behavior of Glass/Epoxy composite material.     

In-plane Compressive Behaviors of 3-D Textile Composites at Various Strain Rates

The in-plane compressive behaviors of 3-D textile composites, which including 3-D woven composite, multi-axial multi-layer warp knitted (MMWK) composite and 3-D braided composite, were studied at quasi-static and high strain rate compression loading. The compression behaviors at high strain rates (600∼2,500/s) were tested with split Hopkinson pressure bar (SHPB). The quasi-static compressive tests were conducted on a MTS 810.23 tester and compared with the results at high strain rates. The comparisons indicate that the compression stiffness, failure stress and failure strain for the three kinds of 3-D textile composites are sensitive to strain rate. The MMWK composite has higher failure stress than the 3-D woven composite and 3-D braided composite at the same strain rate; however, the failure strain of the 3-D braided composites is higher than that of the 3-D woven composite and 3-D knitted composite at quasi-static compression because of the quasi-isotropic structure feature in the 3-D braided composite. The compressive failure modes of the 3-D woven composite, MMWK composite and 3-D braided composite are totally different because of the different preform structure.     

混凝土柱单轴动态抗压特性的应变率效应研究

混凝土材料是典型的率敏感材料,不同动态应变率下混凝土柱的抗压性能有明显的变化。本文通过混凝土柱的轴心动态抗压试验,在10-5/s10-2/s应变率范围内研究了混凝土材料本构关系的应变率效应,系统研究了应变率效应对混凝土抗压强度、弹性模量、峰值应变、吸能能力以及破坏机理的影响,并讨论了试验机刚度、惯性效应对试验结果的影响。试验结果表明：随着应变率的增加,混凝土材料的抗压强度也随之增加,当应变率为10-4/s、10-3/s、10-2/s时混凝土的抗压强度相对准静态抗压强度（应变率为10-5/s）分别增加了7.45%、19.51%和29.23%,弹性模量相对于准静态弹性模量变化不大,峰值应变具有一定的离散性,但是基本趋势也是增加的,混凝土的吸能能力也随着应变率的增加而显著增加。另外,刚性元件的使用有效的改善了试件应变率的稳定性,惯性效应对本次试验结果的影响可以忽略     

Volume fraction effect on high strain rate properties of syntactic foam composites

The volume fraction effect on the high strain rate compressive properties of syntactic foams is characterized using a pulse-shaped Split-Hopkinson Pressure Bar (SHPB) technique. Eighteen different types of syntactic foams are fabricated with the same matrix resin system but six different microballoon volume fractions and three different size microballoons. The volume fractions of the microballoons in the syntactic foams are maintained at 0.1, 0.2, 0.3, 0.4, 0.5, and 0.6. The microballoons have the same mean outer radius of 40 μm, but different internal radii leading to a difference in their density. Analysis is carried out on the effect of microballoon volume fractions on the high strain rate properties for each type of syntactic foam. This approach is helpful in understanding the effect of microballoon reinforcement at different volume fractions on the dynamic compressive properties of syntactic foams. The results at high strain rates are compared to quasi-static strain rate compressive properties of the same material. The results show that there is a decrease in both compressive strength and modulus as the microballoon volume fraction increases for the same type of syntactic foam at all strain rates. However, at strain rates of quasi-static and 450/s, the decrease tends to be gradual across all volume fractions, while for strain rates of 800/s, there is a dramatic decrease from 10 to 20% followed by a gradual decline for most specimens. The fracture mode plays a major role in the dynamic behavior of syntactic foams.     

An Investigation of the Mechanical Behaviors of [45/-45/0/90]ns Satin Weave Composite at Different Loading Rates

The objective of this article is to investigate the compressive behaviors of [45/-45/0/90]_ns satin weave E-7781 glass/Eepoxy composite laminate under different loading strain rates along the in-plane direction. The low strain rate tests were conducted with an INSTRON testing machine, and the high strain rate tests were conducted using a pulse shaper modified compression Split Hopkinson Pressure Bar (SHPB) apparatus. Failure strength and strain at peak stress were evaluated experimentally at different strain rates. The results showed that failure strength and strain at peak stress were rate sensitive. A few strain rate dependent constitutive models were referred to describe the dynamic mechanical behaviors of woven composites with various stacking sequence, and the constants in the equations could be confirmed from experiment data. Optical and microscopic graphs on the specimens were carefully examined to determine operative failure modes. Within the studied strain rate regimes, the failure mode was observed to change from splitting followed by fiber kink banding to predominantly delamination and shear fracture as the strain rate increases from quasi-static to high strain rates.     

Diatom frustule-filled epoxy: Experimental and numerical study of the quasi-static and high strain rate compression behavior

In this study, centric type diatom frustules obtained from a diatomaceous earth filter material were used as filler in an epoxy resin with a weight percentage of 15% in order to assess the possible effects on the compressive behavior at quasi-static and high strain rates. The high strain rate testing of frustule-filled and neat epoxy samples was performed in a split-Hopkinson pressure bar (SHPB) set-up and modeled using the commercial explicit finite element code LS-DYNA 970. Result has shown that 15% frustule filling of epoxy increased both modulus and yield strength values at quasi-static and high strain rates without significantly reducing the failure strain. Microscopic observations revealed two main deformation modes: the debonding of the frustules from the epoxy and crushing/fracture of the frustules. The modeling results have further confirmed the attainment of stress equilibrium in the samples in SHPB testing following the initial elastic region and showed good agreement with the experimental stress–time response and deformation sequence of the samples in high strain rate testing.