Prognostic Value of the Brain CT-Scan in Head Trauma in Yaounde Central Hospital

Introduction: Cranial trauma is a serious medico-surgical pathology that hinders the vital and functional prognosis. The Rotterdam computed tomography (CT) score refined features of the Marshall score. This score was designed to categorize traumatic brain injury (TBI) type and severity in adults. The aim of our research was to evaluate the association between the Rotterdam CT scores of patients after a cranial traumatism in terms of survival. Material and methods: It was a cross-sectional and analytical study from January 2018 to March 2020, using medical records of patients suffering from cranial traumatism, received and taken in charge in the Yaounde central hospital. Results: 100 patients were retained out of 115 recruited patients. The average age was 35.20 with a sex ratio of 4.55. The Rotterdam score was between 1 and 5 with a median of 2. The overall mortality at 6 months and 1 year was 32%. With an equal score compared to European studies, we recorded significantly higher mortality. We found the sequelae in 24% of the patients. GOS ranged from 1 to 5, and survival without sequelae (GOS 1) was the most represented. There was a positive correlation between the Rotterdam score and the GOS with a Pearson correlation coefficient of +0.514. Conclusion: The death rate in Rotterdam score equals is greater in our context compared to European studies.

Nonlinear fluid flow through three-dimensional rough fracture networks:Insights from 3D-printing,CT-scanning,and high-resolution numerical simulations

Nonlinear flow behavior of fluids through three-dimensional(3D)discrete fracture networks(DFNs)considering effects of fracture number,surface roughness and fracture aperture was experimentally and numerically investigated.Three physical models of DFNs were 3D-printed and then computed tomography(CT)-scanned to obtain the specific geometry of fractures.The validity of numerically simulating the fluid flow through DFNs was verified via comparison with flow tests on the 3D-printed models.A parametric study was then implemented to establish quantitative relations between the coefficients/parameters in Forchheimer’s law and geometrical parameters.The results showed that the 3D-printing technique can well reproduce the geometry of single fractures with less precision when preparing complex fracture networks,numerical modeling precision of which can be improved via CT-scanning as evidenced by the well fitted results between fluid flow tests and numerical simulations using CT-scanned digital models.Streamlines in DFNs become increasingly tortuous as the fracture number and roughness increase,resulting in stronger inertial effects and greater curvatures of hydraulic pressure-low rate relations,which can be well characterized by the Forchheimer’s law.The critical hydraulic gradient for the onset of nonlinear flow decreases with the increasing aperture,fracture number and roughness,following a power function.The increases in fracture aperture and number provide more paths for fluid flow,increasing both the viscous and inertial permeabilities.The value of the inertial permeability is approximately four orders of magnitude greater than the viscous permeability,following a power function with an exponent a of 3,and a proportional coefficient b mathematically correlated with the geometrical parameters.

CT-Scan Presentations of Brain Malformations in Children: About Three Cases in Regional Hospital of Ngaoundere-Cameroon

Brain malformations are rare, difficult to diagnose and have unpredictable evolution. They are the major causes of epilepsy, psychomotor development abnormalities and other neurological disorders. The neuroimaging technique of choice for diagnosis of these malformations is magnetic resonance imaging (MRI), but unfortunately MRI is expensive, and is not available in a poor resource country like Cameroon. CT scan associated to clinical signs can help to suspect or to confirm a malformation. The authors report here three cases of malformations discovered during cranial CT scan at the regional hospital of Ngaoundéré. They are Dandy Walker malformation, Sturge Weber’s disease and hemimegalencephaly. These cases contribute to the knowledge of this rare event, and emphasize the importance of CT scan on their diagnosis in the absence of MRI.

Predictive Factors for Abnormal Brain CT-Scan in Childhood Epilepsy at Yaoundé(Cameroon)

Purpose: Despite irradiation, CT-scan remains an important diagnostic tool in epilepsy in poor countries where MRI is neither available nor affordable. But many causes of epilepsy are not accessible to CT-scan and this technique remains expensive for many poor families in countries with limited resources. The aim of this study was to determine clinical or electroencephalogram variables which could predict brain CT-scan abnormalities in childhood epilepsy. Methods: It was a cross-sectional study including 151 epileptic children who underwent head CT-scan from October 2011 to march 2012, in one university-affiliated hospital in Cameroon (YGOPH). The data collected were clinical, type of seizure, Electroencephalogram and head CT-scans results. Independent predictive factors for CT abnormalities were sought by logistic regression. A p value : Of the 151 children, 54.3% (82/151) were boys (sex ratio: 1.18 M/1F). The median age was 54 months [2 - 190 months];74.8% of children were more than 2 years old but at the onset of epilepsy they were 2 years old or less. Birth asphyxia, mental retardation and neurologic deficit were respectively associated in 62.4%, 54.3% and 51.7% of cases. Eighty-five had focal epilepsy (56.3%), 61.6% had abnormal head CT-scan, 68.9% had abnormal EEG, with no significant gender difference. The factors most significantly associated with abnormal head CT-scan were: child age ≤ 2 years, maternal hypertension/eclampsy, cerebral palsy, and child microcephaly, with 89% to 92% abnormal CT. The two independent predictors of abnormal CT were patients’ age ≤ 2 years and microcephaly. The two main CT-scan lesions were cerebral atrophy (28.5%) and brain infarct (16.6%). None of these abnormalities was correlated to any type of epilepsy. Conclusion: Almost two-thirds of head CT-scan performed in epileptic children are abnormal in our setting. Patients of 2 years old or less and those with microcephaly are very likely to have brain anomalies on CT-scan. The most common brain lesions are atrophy, cerebral infarction and porencephalic cavities. Action to reduce birth asphyxia may lead to the reduction of the incidence of epilepsy in children.

Test Accuracy of CT-Scan for the Detection of Malignant Liver Mass

Background: Detection of malignant liver mass is very important for the treatment modalities. Objective: The purpose of the present study was to establish the usefulness of CT scan in the diagnosis of malignant hepatic mass. Methodology: This cross sectional study was carried out in the Department of Radiology and Imaging at Mymensingh Medical College Hospital (MMCH), Mymensingh, Banghabandhu Sheikh Mujib Medical University (BSMMU), Dhaka and Dhaka Medical College Hospital (DMCH), Dhaka during the period of 1st January 2006 to 31st December 2007. Patients admitted in the Department of Medicine and Department of Hepatobiliary of MMCH, BSMMU, and DMCH with the clinical diagnosis of fever, abdominal pain, anorexia, nausea/vomiting, loss of appetite, jaundice, weight loss and ascites were selected as study population. CT scan and histopathology were performed to all the patients. Result: A total number of 50 patients were recruited for this study. Mean age of all patients was 51.28 ± 14 years with a range of 17 year to 78 years. Among all patients 28 had multiple lesion, of them 71.4% was malignant and 28.6% was benign. On the other side 22 patients had solitary lesion, of them 36.4% was malignant and 63.6% was benign

CT-Scan Findings of Hepatic Mass Patients Attending at a Tertiary Care Hospital in Bangladesh

Background: CT-scan is a very useful diagnostic tool for the detection of hepatic mass. Objective: The present study was undertaken to determine the CT-scan findings of benign and malignant hepatic mass patients. Methodology: This was a cross sectional study conducted in Radiology and Imaging Department at Mymensingh Medical College Hospital (MMCH), Mymensingh;Dhaka Medical College Hospital (DMCH), Dhaka and Banghabandhu Sheikh Mujib Medical University (BSMMU), Dhaka with the collaboration of Pathology Department of the same institute for histopathological confirmation. This study was carried out from January 2006 to December 2007 for a period of 2 years. The patients who were clinically suspected of having hepatic mass attended in the Radiology and Imaging Department in the above mentioned institutes were included as study population. All the CT-scan findings were recorded. Result: A total number of 50 patients were enrolled for this study. CT-scan was done among 40 males and 10 females with a mean age of 51.28 years old. Hypodensity was found in 17 (60.7%) and 18 (81.8%) cases in malignant and benign hepatic lesions respectively. Ill-defined margin was detected in 12 (42.9%) and 6 (27.3%) cases respectively. Calcification was present on 11 (39.3%) malignant lesion and 6 (27.3%) benign lesions. Pressure effect on biliary apparatus was found in 11 (39.3%) malignant lesions and 1 (4.5%) benign lesions (p < 0.05). Lymphadenopathy was found in 10 (35.7%) malignant lesions and 1 (4.5%) benign lesions (p < 0.05). Conclusion: In conclusion, CT-scan findings of malignant and benign hepatic mass show hypodensity with more contrast enhancement in malignant lesions with more calcification in malignant lesion;however, significant difference is detected in pressure effect on biliary apparatus and lymphadenopathy.

Prevalence and CT-Scan Presentations of Brain Malformations in Children at a University-Affiliated Mother and Child Hospital (Cameroon)

Background: Brain malformations (BMs) are congenital abnormalities of the shape or structure of the brain, with corpus callosum agenesis known as the most frequent. Diagnosis of most BMs can be prenatal with ultrasound and fetal magnetic resonance imaging (MRI);post-natal diagnosis is based on transfontanellar ultrasound, CT-scan, and head MRI which is the imaging gold standard technique. MRI has been recently introduced and the CT-scan was previously the reference technique for the diagnosis of BMs in our context. Almost no publication has been made in sub-Saharan Africa on the clinical and CT scan characteristics of Brain malformations in children. Objective: The aim of this study was, in the absence of MRI, to describe the clinical and CT-scan presentations of brain malformations in children at the Yaounde Gynaeco-Obstetric and Pediatric Hospital (YGOPH). Patients and method: This was a cross-sectional descriptive study conducted from February to May 2016 at the YGOPH, including all children of 15-year-old and less with BM diagnosed on CT-scan at YGOPH between April 2006 and March 2016. The studied variables were clinical (age at diagnosis, sex, clinical manifestations) and CT findings (type of cerebral malformation). The data was analyzed using the SPSS 20.0 software with the estimation of hospital prevalence of BMs, frequencies and associations. The chi-square test was used to seek for an association between variables. The threshold of significance was p Results: The prevalence of BMs was 0.52%, with 29 cases of BMs identified out of 5590 patients followed up at the pediatric neurology outpatient unit over a period of 10 years. The mean age at diagnosis was 37.2 months (3.1 years) and the most represented age groups were 0 - 1 year (37.9%) and 1 - 5 years (37.9%). The sex ratio was 0.81 (55.2% girls). The clinical presentation was represented by neurological signs (93.1%) with convulsions (65.5%) and psychomotor retardation (58.8%) associated with skin lesions (34.5%) and/or facial dysmorphic features (27.6%). BM was suspected on antenatal ultrasound in 14.3% of cases (4/28). Abnormalities of cortical development accounted for 65.5% of BM followed by abnormalities of brain separation (31%). Tuberous sclerosis complex was the most common BM (31%) followed by agenesis of the corpus callosum (27.6%). The presence of dysmorphic facial features was associated (p = 0.007) with disorders of brain separation (DBS) while the presence of cutaneous lesions was associated (p = 0.013) with anomalies of the cortical development (ACD) especially tuberous sclerosis complex. Conclusion: BMs are infrequent, dominated by tuberous sclerosis complex and agenesis of the corpus callosum. They are mainly revealed by convulsions and psychomotor retardation. Efforts are needed to improve antenatal diagnosis and facilitate access to cerebral MRI.

基于CT技术的黄原胶加固土干湿循环条件下力学性能和微观结构劣化机制研究

干湿循环对岩土体的工程特性具有重要影响。采用CT扫描技术和力学测试,对加入不同含量黄原胶(0%,0.5%,1.5%)加固的黏土在经历不同次数(0,1,4,8,12次)干湿循环作用下的力学性能和微观结构劣化机制进行了研究,得到结论:(1)黄原胶能够有效提高土体的抗压强度和耐干湿循环效果。随着黄原胶含量的增加,干湿循环作用后的强度损失逐渐减小,当循环次数从0次增加到4次时,对于加入黄原胶含量分别为0%,0.5%,1.5%的试样,抗压强度分别损失了42.75%,17.2%,14.04%。(2)加固土的抗压强度与干湿循环次数之间保持指数下降的关系,当循环次数达到4次后,随着循环次数的进一步增加,抗压强度和弹性模量均在较小的变化范围内波动。(3)随着干湿循环次数的增加,黄原胶加固土的孔隙率表现出先增加后减小的趋势,连通孔隙不断扩展,而孤立孔隙表现出先增加后减小的趋势。(4)随着试样的干燥,黄原胶在土颗粒间形成网状基质,提高土体的强度和耐干湿循环能力。

苏北盆地古近系阜宁组二段页岩油储层岩石力学特征及其控制因素

为查明苏北盆地页岩油储层可压性特征及压后孔、缝变化规律,以古近系阜宁组二段(阜二段)为研究对象,对岩石力学特征、压裂效果及其影响因素进行研究。用计算机高分辨断层扫描成像技术(多尺度CT扫描)对岩样进行三维重构,获取孔、缝结构参数;开展地层围压下三轴力学实验,获取岩石力学参数;将压裂后的岩样按相同位置和方向再次进行多尺度CT扫描,获取压裂后三维孔、缝结构图像。根据应力-应变曲线特征,将本区页岩划分为3种类型。①1型页岩,为破裂曲线波浪下降,压后形成复杂网状缝页岩。②2型页岩,为破裂曲线类型多样,具波浪下降和垂直下降形状,压后缝网较发育的页岩。③3型页岩,为破裂曲线垂直下降,破裂后整体较完整,压后多形成纵向劈裂缝、缝网不发育的页岩。这3种类型页岩压后孔隙变化特征是:1型和2型页岩直径10~50μm孔隙占比减少,直径50~100μm孔隙增多,直径300μm以上孔隙孔容贡献增大;3型页岩压裂前、后孔径分布及孔容贡献变化不明显。研究表明,抗压强度与弹性模量、剪切模量具有正相关关系,与泊松比具有V型曲线关系;碳酸盐和黏土矿物含量是控制本区页岩力学性质的主要因素,石英和有机碳含量为次要因素。孔隙度及纹层发育特征是页岩储层可压性特征的重要影响因素。

冲击载荷下含瓦斯煤动力学破坏特征与瓦斯渗流规律分析

为探究不同冲击载荷和瓦斯压力作用下的含瓦斯煤动力学特征、裂隙扩展及瓦斯渗流变化规律,采用含瓦斯煤岩冲击损伤-渗流试验系统开展含瓦斯煤冲击试验以及原位渗流测试,并结合工业CT扫描系统进行试样裂隙结构的三维重构,分析含瓦斯煤内部裂隙扩展特征及其对瓦斯渗流的影响规律。研究结果表明,冲击载荷和瓦斯压力对含瓦斯煤的动力学性质、变形过程、裂隙扩展和渗流规律均具有重要影响,具体表现在:①受围压和轴压的影响,冲击载荷耦合瓦斯压力条件下的含瓦斯煤应力-应变曲线无明显压密阶段;含瓦斯煤的变形过程主要经历了弹性变形阶段、应变强化阶段及破坏阶段。②冲击载荷的增加对含瓦斯煤动力学参数具有强化作用,气体压力的升高则劣化了含瓦斯煤动力学参数;冲击载荷越大,瓦斯压力越高,含瓦斯煤的裂隙扩展愈充分,所形成的裂隙结构愈复杂。③含瓦斯煤的渗流规律受控于裂隙扩展,冲击载荷耦合瓦斯压力作用下,含瓦斯煤中存在孔隙流动、孔隙流动-裂隙流动并存及裂隙流动等3种气体流动形式;含瓦斯煤冲击破坏后,随着气体压力增加以及气楔作用的增强,瓦斯流动形式可由孔隙流动依次转变为孔隙流动-裂隙流动并存和裂隙流动;裂隙扩展和流动形式共同影响含瓦斯煤渗流规律,含瓦斯煤渗透率随瓦斯压力的增大总体上符合先增大后减小的变化趋势。

单轴压缩下松软煤体波速演化与裂隙分布特征

为研究松软煤体超声波传播规律与破坏特征,选用型煤代替原煤,设定3条波速传播路径,运用MTS岩石力学实验机、PCI-Ⅱ声发射仪开展单轴压缩条件下煤体多路径波速同步监测试验,引入各向异性指数分析波速演化规律;选定3个横、纵向切面,采用CT扫描设备开展破坏特征观测试验,重构破坏后煤体细观几何结构,对比研究二维横纵切面裂隙分布差异性;探讨波速和三维裂隙体积的关系。结果表明:①随轴向应变的增加,平行、垂直加载方向及煤体平均波速均表现出先平稳后降低再平稳的基本规律,波速各向异性指数具有先平稳后增大再平稳的变化趋势;垂直加载方向波速最先下降,且降幅最大。②与纵向切面相比,破坏后煤体横向切面裂隙谱峰占比和裂隙分形维数均较大,裂隙密度较高,裂隙形态也较为复杂。③随裂隙体积的增大,破坏后煤体平均波速大致呈线性降低,单轴荷载作用下煤体内部裂隙扩展以平行加载方向为主,裂隙竖向线状扩展是造成各方向波速和横纵切面破坏特征差异性的主要原因。④与平行加载方向相比,采用垂直加载方向波速求得的损伤变量较大、评价煤体损伤破坏状态也更为可靠。现场采用声波评价煤体破坏状态时,将声波传播路径设置为垂直煤体受载(最大主应力)方向,有利于提高预测失稳事故的合理性。

基于CT断层扫描的木质家具与原木内部缺损三维可视化研究

研究木质家具与原木试件内部缺损三维可视化,有助于木质文物精准干预性保护与木材高效规划利用。凸显三维成像技术可视化优势,对木质文物保护具有重要意义。本文采用philips16排CT——A机型Brilliace16对试件三维断层扫描。通过对CT扫描后原始图像的分割,获取品质较佳的三维数字模型。继而对分割后的图像进行切面与断面两个维度的手工着色,随后通过三维重建可得到开裂、虫洞、朽坏等不同形式缺损的三维形态,并可得到与之对应的精准三维模型。试验证明:通过三维重建,可获取木质试件内部不同类型三维缺损形态的可视化分析,可对缺损形态进行360°观察,并可获取三维缺损形态的表面积、体积等精准物理参数。本技术可为木质文物修复提供三维缺损形态的精准参数及直观可视化三维模型。

肠腔内型机械性小肠梗阻13例的诊断和治疗体会

目的探讨肠腔内型机械性小肠梗阻的诊断和治疗体会。方法采用回顾性、描述性的研究方法。收集2016年10月至2022年5月首都医科大学附属北京友谊医院普通外科收治的13例肠腔内型机械性小肠梗阻的完整临床资料。所有患者术前均有不同程度的“痛、吐、胀、闭”等肠梗阻症状,术前均行急诊全腹CT平扫,并经过手术验证诊断。结果将13例肠腔内型机械性小肠梗阻分为4种病因:胆石性3例、非食源性异物1例、食源性粪石8例、血块性1例。胆石性组梗阻3例,均有胆囊结石病史且有典型的肠梗阻症状,全腹CT平扫提示Rigler三联征;3例患者均在急诊手术将梗阻远端约5~10 cm正常小肠对系膜缘纵行切开,将胆石挤向远端取出、近端肠管减压术。非食源性异物梗阻1例,有吞服胶囊内镜检查病史,术前出现肠梗阻症状;全腹CT平扫提示:小肠可见极高密度影(金属),近端肠管明显扩张、积液;术中将梗阻远端约10 cm正常回肠对系膜缘纵行切开,将异物挤向远端取出,近端肠管减压术。食源性粪石梗阻8例,有多次空腹食用“生柿子、生山楂、生李子或芒果”病史,术前出现肠梗阻症状;全腹CT平扫提示小肠病变完全充填梗阻节段肠腔,致使肠腔明显扩张;病灶密度均为夹杂气泡的“蜂窝状”或“筛孔状”,边界清楚有包壁征;术中将梗阻远端约10 cm正常小肠对系膜缘纵行切开,将粪石挤向远端取出,近端肠管减压术。血块性梗阻1例,患者有食用“生山楂”病史,术前出现肠梗阻症状;CT平扫提示肠道内多发小肠残渣征表现,故临床上误诊为“粪石梗阻”伴严重感染(白细胞快速异常增高)而行手术治疗,术中未发现明确机械性肠梗阻;术后胃镜提示胃贲门撕裂伤、活动性出血,予钛夹止血。结论肠腔内型机械性小肠梗阻病因繁杂,容易造成误诊,在临床实践中应该重视病史、查体,尤其是腹部CT扫描对诊断有重要价值。充分认识及时判定小肠梗阻的病因是及时制定合理治疗方案的关键。

3D打印混凝土抗碳化性能各向异性及成因分析

受挤出式工艺的影响,3D打印混凝土中存在较多的界面,影响着打印混凝土的耐久性能。为了探明3D打印成型混凝土抗碳化性能的各向异性变化规律,通过碳化试验研究了三种水胶比3D打印混凝土沿X、Y、Z三个方向的碳化行为。基于压汞试验和X-CT扫描获取了3D打印混凝土的孔隙特征和分布规律,从微观层面阐释3D打印混凝土抗碳化性能的变化机理。结果表明:孔隙与3D打印混凝土的碳化行为有着密切联系,层条间界面因条带堆叠产生了更多孔隙,因而CO_(2)在界面位置扩散速度更快,碳化深度更大;受界面的影响,打印混凝土的抗碳化性能具有明显的各向异性;基体部位材料的抗碳化性能优于层间界面,层间界面的抗碳化性能优于条间界面;水灰比越低,材料抗碳化性能越好;当CO_(2)在混凝土中扩散时,受层条间大孔隙的影响,打印成型混凝土中形成了未碳化岛。

基于CT扫描受压注浆体试块三维孔裂隙结构参数表征

目的为研究注浆体试块单轴压缩过程中孔裂隙结构演化特征,方法以级配砂砾注浆体试块为研究对象,对其单轴压缩过程分阶段进行工业CT扫描,并采用AVIZO对CT切片进行分析,重构孔裂隙结构三维模型,定量表征孔裂隙与孔喉特征参数。结果结果表明:单轴压缩下,试块依次经历孔裂隙萌生、发育、扩展与贯通阶段,孔裂隙演化特征比较明显,萌生阶段孔隙数增幅为14.41%,无明显贯通;发育阶段孔隙数增加326.91%,伴有一定数目孔隙贯通;扩展阶段孔隙数减少了57.79%,孔隙等效直径最大值增幅为223.45%,大部分孔隙贯通为裂隙;贯通阶段孔裂隙数目几乎不变,孔隙等效直径最大值增幅为92.83%,裂隙贯通后形成多个破裂面。峰值后试块出现连通孔隙,该阶段注浆体孔隙与喉道发育完全,试块破坏。结论研究结果可为后续破碎岩石注浆工程实践提供参考。

CT增强扫描灰度直方图纹理分析技术对肺癌患者术前恶性程度评估及对预后的预测价值

目的探究CT增强扫描灰度直方图纹理分析技术对肺癌患者术前恶性程度评估及对预后的预测价值。方法选择2018年5月至2022年9月在我院就诊的且经术后病理证实的肺癌患者580例作为研究对象。依据术后病理分期,将研究对象分为高分化组(183例)、中分化组(195例)、低分化组(202例)。根据预后情况,将其分为预后良好组(356例)和预后不良组(224例)。由2名医师提取患者CT增强扫描灰度直方图纹理参数。受试者工作特征(receiver operating characteristic,ROC)曲线分析特征参数对肺癌患者术前恶性程度的诊断效能及预后的预测价值。多因素Logistic回归分析预后不良的重要影响因素并构建人工神经网络模型。Pearson分析检验参数间的相关性。结果均值、10%分位、50%分位等参数在高、中、低分化三组中有显著差异。三个参数对评估肺癌患者恶性程度均具有一定的诊断效能,且三者联合诊断效能最佳。均值、10%分位、50%分位是预后不良的保护因素,三者联合预测肺癌患者的曲线AUC值大于各指标单独预测的AUC值。ROC曲线和累积增益图表明该模型预测能力良好。纹理特征参数中,69.44%的参数具有相关性。结论CT增强扫描灰度直方图纹理参数在一定程度上反应肺癌患者术前恶性程度信息,给术前预测以及预后提供了重要方法。

A shield of defense:Developing ballistic composite panels with effective electromagnetic interference shielding absorption

The primary goal of this study is to develop cost-effective shield materials that offer effective protection against high-velocity ballistic impact and electromagnetic interference(EMI)shielding capabilities through absorption.Six fiber-reinforced epoxy composite panels,each with a different fabric material and stacking sequence,have been fabricated using a hand-layup vacuum bagging process.Two panels made of Kevlar and glass fibers,referred to as(K-NIJ)and(G-NIJ),have been tested according to the National Institute of Justice ballistic resistance protective materials test NIJ 0108.01 Standard-Level IIIA(9 mm×19 mm FMJ 124 g)test.Three panels,namely,a hybrid of Kevlar and glass(H-S),glass with ceramic particles(C-S),and glass with recycled rubber(R-S)have been impacted by the bullet at the center,while the fourth panel made of glass fiber(G-S)has been impacted at the side.EMI shielding properties have been measured in the X-band frequency range via the reflection-transmission method.Results indicate that four panels(K-NIJ,G-NIJ,H-S,and G-S)are capable of withstanding high-velocity impact by stopping the bullet from penetrating through the panels while maintaining their structural integrity.However,under such conditions,these panels may experience localized delamination with variable severity.The EMI measurements reveal that the highest absorptivity observed is 88% for the KNIJ panel at 10.8 GHz,while all panels maintain an average absorptivity above 65%.All panels act as a lossy medium with a peak absorptivity at different frequencies,with K-NIJ and H-S panels demonstrating the highest absorptivity.In summary,the study results in the development of a novel,costeffective,multifunctional glass fiber epoxy composite that combines ballistic and electromagnetic interference shielding properties.The material has been developed using a simple manufacturing method and exhibits remarkable ballistic protection that outperforms Kevlar in terms of shielding efficiency;no bullet penetration or back face signature is observed,and it also demonstrates high EMI shielding absorption.Overall,the materials developed show great promise for various applications,including the military and defense.

煤张开型裂隙三维宏细观演化特征及扰动因素探究

裂隙演化方式受控于诸如矿物特征及围压条件等内外环境,为探究含裂隙煤体裂隙宏细观演化特征及影响因素的围压效应,基于工业CT扫描系统及其搭载的三轴加载系统对含裂隙煤体开展三轴静载试验,以多角度联合表征,对原生裂隙、矿物及围压的内外条件相互作用机制做出合理解释。结果表明:①围压会改变煤体初始损伤显著区位置,使其随围压升高由裂隙尖端过渡至煤体上、下端,且微孔隙和大尺寸裂隙之间比微孔隙和微孔隙之间更易相互贯通,并产生新的宏观裂纹。②围压升高使得三维动态分形维数由缓慢增加、快速增加和平稳增加转变为平稳增加、快速增加和缓慢增加的发展阶段,可表征裂隙的时间演化规律。③含裂隙煤体在单轴或低围压下呈纵向拉伸破坏,高围压会使其破坏方式趋于剪切,并通过2种途径提升煤体强度。④起裂角理论值偏离试验值程度随围压增加而增加,与煤体由矿物分布引起的离散度数值关系一致。⑤根据裂隙的受力成分及矿物分布特征将裂隙扩展行为分为直驱、绕核和错核3种类型,该扩展行为受围压对裂隙的作用力成分影响,由相对纯粹拉应力、拉伸–剪切复合应力和相对纯粹剪应力作用的裂纹分别对应以上3种扩展行为,即对裂隙的扩展影响形式表现为以围压为主,矿物赋存形态为辅。

爆后岩石裂隙结构可视化及定量表征方法

爆后岩石破坏特征的定量表征一直是工程爆破领域急需解决的关键问题,爆后岩石裂纹萌生、扩展演化直至贯通的过程是导致岩石破裂的主要原因。为了研究被爆岩石内部裂纹扩展和断裂模式的演化过程,利用工业CT对爆后岩石进行扫描观测,通过图像堆栈矢量化处理构建岩石三维裂隙模型,并对裂纹结构特征参数进行统计分析,定量化表征岩石破坏程度及裂纹扩展情况。结合数值模拟分析爆炸冲击波压力的衰减规律,通过SEM电镜扫描试验研究爆破过程中不同位置岩石的微观形貌特征,对比断口元素成分变化与断裂模式的关联机制。研究结果表明:用等效球体方法对岩体内不同尺度裂隙结构进行统计分析,微裂隙数目多且分布均匀,主裂隙体积大且连通性较好。随着裂隙等效球体直径的增加,裂隙表面积和体积整体上呈上升趋势;三维重构裂隙结构中裂隙率可以表征岩石局部裂纹扩展特征,爆炸近区裂隙率和三维分形维数远大于爆炸中远区的裂隙率和分形维数,说明岩石破裂过程中裂隙扩展演化主要在此阶段进行;相较于爆炸中远区,爆炸近区冲击波压力峰值高且衰减速率慢,使得整个爆破过程岩石微观断裂模式变化较大,大致呈现出由沿晶断裂向穿晶断裂、脆性断裂向塑性破坏的方向进行,非金属元素质量的变化对于各阶段断裂模式转变具有显著影响,断裂模式转变区域非金属元素质量发生明显减小。随着爆破作用的减弱,岩石破裂逐渐趋于无序和紊乱,破裂时断口也不限于解理面和晶粒边界。