Experimental investigation on hard rock fragmentation of inserted tooth cutter using a newly designed indentation testing apparatus

This investigation aims to explore the effects of stress conditions and rock cutting rates on hard rock fragmentation through indentation tests on a newly designed triaxial testing apparatus.This apparatus was designed to realize a triaxial loading and indentation test of cylindrical specimens using inserted tooth cutter.The boreability and crushing efficiency of granite rock was investigated by analyzing the change rules of the thrusting force,penetration depth,characteristics of chippings and failure patterns.Several quantitative indexes were used to evaluate rock boreability in this investigation.The granite rock samples all had a chiselled pit and a crushed rock core.Under initial stress conditions,only flat-shape chippings were stripped from the rock surface when the thrusting force reached 20 kN.The rock cutting special energy had a close correlation with the initial stress conditions and inserted tooth shape.Moreover,a thrusting force prediction model was proposed in this paper.The contribution of this study is that for the first time the influence mechanism of the initial triaxial stress conditions on rock fragmentation is investigated using an inserted tooth and the newly designed testing apparatus.This study has a crucial importance for practical underground hard rock crushing in geoengineering.

Occlusal tooth wear in human sculls of antique period from Vendenis and Municipium Dardanorum DD, Kosovo

Aim: To describe the presence, frequency of attrition in permanent dentition of human skulls from two ancient archeological locations. Aims: To determine the rate of attrition using a specific quantitative and qualitative method. Methods: Twenty one human skulls from two ancient archeological necropolises (Vendenis and Municipium Dardanorum DD) were included in the analysis of samples for this study. A total of 498 teeth were present in all human skulls. The skulls (with their accompanying teeth) were then divided into groups according to locality of origin, age and sex. Macroscopic (observational) analysis of the teeth relied on inspection and exploration of the teeth in their totality. The classification system that was used to rate tooth wear was Tooth Wear Index (TWI). Statistical analysis used: Chitest for small samples was used to evaluate the observations obtained from the study. Multiple Logistic Regression Analysis was not performed due to the small number of teeth and the content of zero values in respective age groups. Results: The results show that out of total 498 teeth, 89.35% had attrition and 10.65% had no attrition or Grade 0 TWI. 21.48% were Grade 1, 28.71% Grade 2, 26.90% Grade 3, 7.42% Grade 4 and 4.81% Grade 5. Conclusions: Grade 2 and higher rate of attrition, was predominantly present in first permanent molars.

Micro-scale Abrasion and Medium Load Multiple Scratch Tests of PVD Coatings

Micro-scale abrasion testing is widely used to determine the abrasion resistance of thin film coatings; it is a simple technique that can easily be used as part of a quality control procedure, but it has got the disadvantage of not allowing an easy study of the wear mechanisms involved: it is difficult to estimate the load applied on each abrasive particles in the contact between the loaded ball and the specimen. The possibility of using progressive loading scratch testing, a method widely used to assess the adhesion of thin film coatings, to model the abrasive wear of coatings has been studied in the past; the use of multiple scratch tests to study the wear mechanisms corresponding to a single abrasion scratch event has also been studied in the case of bulk materials (ceramics and hard metals). Two coatings, deposited by Closed Field Unbalanced Magnetron Sputter Ion Plating (CFUBMSIP) on ASP23 powder metallurgy steel substrate are chosen to be representative of the use of protective coatings in industry: titanium nitride, which is widely used to prevent tool wear, and TCL Graphit-iC?, which is widely used as a wear resistant solid lubricant coating. The two coatings are first characterised by using a standard quality control procedure: their thickness is determined by the cap grinding method, their adhesion by progressive loading scratch. Then micro-scale abrasion tests performed with a slurry at a concentration which promotes grooving wear, and medium load multiple scratch tests performed with diamond indenters are completed; the results of these tests are analysed and compared to determine if there is any correlation between the two sets of results; the multiple scratch tests wear tracks are also observed to determine the wear mechanisms involved.

Nine-hole Peg Test and Ten-meter Walk Test for Evaluating Functional Loss in Chinese Charcot-Marie-Tooth Disease

Background：The 9-hole peg test （9-HPT） and 10-meter walk test （10-MWT） are commonly used to test finger motor function and walking ability.The aim of this present study was to investigate the efficacy of these tests for evaluating functional loss in Chinese Charcot-Marie-Tooth （CMT） disease.Methods：Thirty-four Chinese CMT patients （CMT group） from August 2015 to December 2016 were evaluated with 9-HPT,10-MWT,CMT disease examination score,overall neuropathy limitation scale （ONLS）,functional disability score,and Berg Balance Scale （BBS）.Thirty-five age-and gender-matched healthy controls （control group） were also included in the study.Student＇s nonpaired or paired t-test were performed to compare data between two independent or related groups,respectively.The Pearson test was used to examine the correlations between recorded parameters.Results：The mean 9-HPT completion time in the dominant hand of CMT patients was significantly slower than that in the healthy controls （29.60 ± 11.89 s vs.19.58 ± 3.45 s;t =-4.728,P 〈 0.001）.Women with CMT completed the 9-HPT significantly faster than men with CMT （dominant hand：24.74 ± 7.93 s vs.33.01 ± 13.14 s,t =2.097,P =0.044）.The gait speed of the average self-selected velocity and the average fast-velocity assessed using 10-MWT for CMT patients were significantly slower than those in the control group （1.03 ± 0.18 m/s vs.1.44 ± 0.17 m/s,t =9.333,P 〈 0.001;1.31 ± 0.30 m/s vs.1.91 ± 0.25 m/s,t =8.853,P 〈 0.00 1,respectively）.There was no difference in gait speed between men and women.Both 9-HPT and 10-MWT were significantly correlated with the ONLS,functional disability score,and BBS （P 〈 0.05 for all）.Conclusion：The 9-HPT and 10-MWT might be useful for functional assessment in Chinese patients with CMT.

Reliability of Sawai's classification for dental cervical abrasions:A pilot study

AIM To test the reliability of the Sawai’s classification for dental cervical abrasions.METHODSIntraoral photographs of 70 teeth from 23 patients with tooth abrasions were taken by the first examiner MS.The teeth were marked and the photos were maintained in a soft copy sequentially.Two other examiners FA and SC were trained in the use of the classification and any clarifications needed were provided at the beginning of the study.Each examiner was then given the soft copy of the complied photographs and was asked to classify the dental cervical abrasion according to their understanding of the Sawai’s classification.They were given sheets to write their responses for every marked tooth.All the examiners were blinded to each other’s observations which were then tested for inter-rater agreement among the three examiners.RESULTSThe 70 teeth with tooth abrasions from 23 patients were examined by 3 investigators(MS,FA and SC)to test the reliability of the Sawai’s classification system for tooth abrasion.Each examiner marked their responses in separate sheets which were blinded to each other.The kappa statistics were performed for inter-rater agreement among the three examiners.The level of agreement was evaluated according to the six-level nomenclature given by Landis and Koch.ICC and 95%CI between two examiners,i.e.,the inter-rater agreement among 1^(st) examiner(MS) and 2^(nd) examiner(FA) was 0.89.The inter-rater agreement among 1^(st) examiner(MS) and 3^(rd) examiner(SC) was 0.89.And the inter-rater agreement among 2^(nd) examiner(FA) and 3^(rd) examiner(SC) was 0.83.All the three comparisons show an almost perfect agreement between them.CONCLUSIONThere is an almost perfect agreement between multiple observers for classifying dental cervical abrasions using Sawai’s classification.Hence,this classification is reliable.

不同几何尺寸SiC微粒对机床导轨材料GCr15的磨损机制

目的探究不同几何尺寸SiCf/SiC陶瓷基复合材料切屑对机床精密部件磨损性能的影响机制及磨损机理,为机床防护提供理论参考。方法以机床精密部件——导轨运动副为例,利用SiC磨粒代替SiCf/SiC陶瓷基复合材料切屑,采用机床导轨运动副材料GCr15轴承钢,在不同几何尺寸磨粒条件下进行销盘摩擦磨损试验,采用宏观摩擦因数和微观磨损形貌对磨损表面进行表征,探究磨损机制。结果相较于无磨粒条件下,在加入磨粒后其摩擦因数更高、更不稳定。在磨粒条件下,GCr15轴承钢的磨损表面存在大量的平行凹槽和不规则压痕,并伴随着少量的剥落坑。随着磨粒尺寸的增加,损伤加重,平行凹槽磨损更深、更宽,表面材料的剥落坑更密集,同时,磨粒几何尺寸的增加导致更深的磨痕深度及更高的磨损量。结论磨粒在摩擦界面存在游离和结合等2种运动形式,磨损机制为滚动挤压磨损与滑动开槽磨损的结合,且随着磨粒几何尺寸的增大,磨损机制由磨粒滚动挤压过渡为滑动开槽主导;1μm和5μm磨粒对摩擦进程的影响主要体现在剧烈磨损阶段,而10μm和20μm磨粒对整个进程都有明显影响,且大尺寸磨粒的加入会使摩擦副提前进入剧烈阶段;对比不同条件下的磨损形貌、摩擦因数及磨损量可知,1μm和5μm的磨粒对摩擦的影响较小。

Research of Test Method on Abrasion Resistance at Elevated Temperatures of Refractories

In this work,the factors and parameters of a test method on abrasion resistance at elevated temperatures were discussed and researched.First of all,the precision tests of the test method on abrasion resistance at elevated temperatures were conducted in 8 laboratories.The results such as the standard deviation and reproducibility show good repeatability and reliability.The relationship between the stability of refractory performance and the standard deviation of their wear value was analyzed.Then the impact of the heat treatment condition of unshaped refractories and oxidation of SiC sand as abrasive on the lost volume of the tested specimens was researched.

A New Test Method for Hot Abrasion Resistance on Refractories

Test methods for hot abrasion resistance of refractories in China and overseas were briefly introduced. A new test method for hot abrasion resistance was researched. The new method inherits test principle of cold abrasion resistance in Chinese standard totally, adopts compressed air pre-heating and electricity heating sam- ples, and is featured with complete structure, good con- trollability, simple operation, and small size. The characteristics and operating procedure of HAT-14A tester were introduced. The hot abrasion resistance of various refractories at different temperatures was tested.

Chinese Standards on Refractories Refractory Products-Determination of Abrasion Resistance at Ambient Temperature GB/T 18301-2012

This standard specifies the terms and definitions, theory, apparatus, specimens, test procedures, calcu- lation results, apparatus check and test reports, etc. of abrasion resistance at ambient temperature of refractory products.

Effects of personalized oral hygiene management on oral health status of pregnant women

BACKGROUND The Cariostat caries activity test(CAT)was used to evaluate the effectiveness of personalized oral hygiene management combining oral health education and professional mechanical tooth cleaning on the oral health status of pregnant women.AIM To investigate whether personalized oral hygiene management enhances the oral health status of pregnant women.METHODS A total of 114 pregnant women who were examined at Dalian Women’s and Children’s Medical Center were divided into four groups:High-risk experimental group(n=29;CAT score≥2;received personalized oral hygiene management training),low-risk experimental group(n=29;CAT score≤1;received oral health education),high-risk control group(n=28;CAT score≥2),and low-risk control group(n=28;CAT score≤1).No hygiene intervention was provided to control groups.CAT scores at different times were compared using independent samples t-test and least significant difference t-test.RESULTS No significant difference in baseline CAT scores was observed between the experimental and control groups,either in the high-risk or low-risk groups.CAT scores were reduced significantly after 3(1.74±0.47 vs 2.50±0.38,P<0.0001)and 6 months(0.53±0.50 vs 2.45±0.42,P<0.0001)of personalized oral hygiene management intervention but not after oral health education alone(0.43±0.39 vs 0.46±0.33,P>0.05 and 0.45±0.36 vs 0.57±0.32,P>0.05,respectively).Within groups,the decrease in CAT scores was significant(2.43±0.44 vs 1.74±0.47 vs 0.53±0.50,P<0.0001)for only the high-risk experimental group.CONCLUSION Personalized oral hygiene management is effective in improving the oral health of pregnant women and can improve pregnancy outcomes and the oral health of the general population.

网格化磨料射流割缝辅助截齿破岩试验研究

针对煤矿岩巷掘进过程中截齿破岩能力不足、效率低、磨损快等问题,提出了网格化磨料射流割缝辅助截齿破岩方法,并进行了正交化物理模拟试验,研究了工况参数对破岩效果的影响。结果表明:(1)磨料射流对岩石预制割缝,能够显著提高截齿单位时间的破岩体积,且试验中网格尺寸和割缝深度取值越大,破岩效率越高。(2)当射流割缝辅助破岩时,截齿等效应力峰值和均值均显著降低,有效减少截齿磨损。(3)网格化磨料射流辅助截齿破岩参数的优选工况组合为:横向和纵向网格尺寸分别为44、30 mm,喷嘴进给速度为600 mm/min。研究成果为网格化磨料射流辅助机械截齿破岩技术推广应用提供了理论基础与数据支撑。

复杂内孔结构磨粒流加工的检测评价与优化

为提高军工零件的内孔加工的可靠性和加工质量,通过正交试验法,分析磨粒流加工中,磨料粒度、磨料质量分数、磨粒流工作压力和循环加工次数对阶梯内孔倒圆角半径、材料去除率、内孔表面粗糙度的影响规律,磨粒流工作压力是内孔倒圆角半径的首要影响因素,较为显著,材料去除率的首要影响因素是磨料质量分数,而内孔表面粗糙度的首要影响因素是循环加工次数,通过非线性回归分析建立了复杂内孔磨粒流加工效果评价的模型。以改进的带精英策略的快速非支配排序遗传算法(NSGA-II)进行多目标工艺参数寻优,得到了综合平衡权重下的最佳工艺方案(磨料粒度1 000#,磨料质量分数为50%,工作压力为7.5 MPa,循环加工次数为30次),验证试验表明优化结果和实际加工效果具有较好的一致性。

镐齿滚刀的齿形及布齿参数优化试验研究

为研究镶齿滚刀上镐齿的齿形参数以及齿间距、排间距对其破岩效率及齿下岩石损伤区的影响规律,选用不同齿形的镐齿对尺寸为300 mm×300 mm×300 mm北山花岗岩进行侵入破岩试验,对镐齿侵入试验过程、侵入力、破岩体积、破岩效率、齿下岩石损伤区特征进行分析。试验结果表明:1)所选试验齿形中直径为18 mm镐齿破岩效率最高;2)齿间距和排间距为35~40 mm时,镐齿侵入破岩效率最高;3)应用荧光裂纹显现法分析齿下岩石裂纹分布特征,获得了不同齿形参数下岩石损伤区范围及裂纹扩展模式、裂纹特征分析结果,与通过侵入力、破岩比能分析得出的破岩效率结论一致。

基于滚刀Cerchar磨蚀性指数的滚刀磨损量预测方法

为探究正常磨损机制下的滚刀磨损特性及对滚刀磨损量进行预测,根据盘形滚刀实际几何尺寸制作了比例为1∶10的缩尺滚刀,使用SP3-I滚刀复合磨蚀实验平台开展6种硬度刀具的滚刀旋转磨蚀试验,分析滚刀硬度对滚刀磨损量的影响规律。利用ATA-IGG I类岩石磨蚀伺服实验仪器进行不同硬度滚刀的Cerchar磨蚀试验,引入滚刀Cerchar磨蚀性指数,通过滚刀Cerchar磨蚀试验测得滚刀CAI(cerchar abrasivity index)值,基于滚刀CAI值提出了基于滚刀Cerchar磨蚀性指数的滚刀磨损量预测方法。结果表明:不同硬度滚刀在同种岩石条件下,其滚刀磨损量随着滚刀硬度增大呈现出先减小后增大的趋势,对于同一种岩石类型,存在一个最佳的刀具硬度区间,使用该硬度范围的滚刀可以提高施工效率;依据滚刀CAI值及其滚刀千米磨损量之间的拟合曲线,得出当前工况下花岗岩、砂岩、玄武岩中的滚刀磨损量计算公式,选取单一滚刀在花岗岩中进行旋转磨蚀试验,通过验证对比,该预测方法得出的预测磨损量与实际磨损量的平均误差在10%以内。

硬岩地质下镶齿滚刀齿形对破岩性能影响研究

为了降低镶齿滚刀的破岩比能耗和刀齿接触面应力,提高镶齿滚刀在硬岩地质下的破岩效率和使用寿命,采用LS-DYNA建立显示动力学仿真模型,并通过实验验证模型的可靠性。仿真分析镶齿滚刀的破岩机理及不同齿形的破岩效率,确定较优的齿形。通过正交试验法,分析齿宽、齿高、齿顶半径和齿数对破岩效率以及接触面应力值的影响,确定齿形参数对破岩性能影响权重。研究结果表明:在118 MPa硬岩地质下,镐齿滚刀的破岩效率最高,齿顶半径为破岩效率的最主要影响因素,权重达到50%,齿数与齿顶高为接触面应力值的主要影响因素,权重分别占31%、36%。齿形最优参数组合是齿宽为11 mm、齿顶高为1 mm、齿顶半径为10 mm、齿数为36个。该研究对于镶齿滚刀的齿形选择及参数优化具有参考价值。

放矿作用下改性尾砂覆盖层颗粒磨蚀性实验研究

作为覆盖层的改性尾砂损耗程度对露天转地下矿山的安全起着重要作用。为此,依托庙沟铁矿露天转地下矿山回采条件,采用模型试验方法,研究了改性尾砂作为覆盖层在放矿过程中的运动规律与磨蚀性。实验结果表明:受侧面墙体限制的左右区域的改性尾砂颗粒,其整体运移要比中间区域的改性尾砂颗粒整体运移量大;在放矿过程中改性尾砂颗粒的质量损失与其运移距离成正比;根据区域初始总质量、放矿循环数与放矿后的区域质量拟合得到放矿循环数与放矿后改性尾砂颗粒整体质量的关系式,由此得到了改性尾砂颗粒磨蚀性在前三个循环放矿过程中不断降低,之后其磨蚀性相对稳定的结论。研究成果对覆盖层磨蚀导致的安全问题有一定的理论参考价值。

基于应变测试的风电齿轮箱行星轮轴承载荷作用中心的确定

行星轮轴承是风电齿轮箱的关键部件,因其位置的特殊性和受载的复杂性,在风电齿轮箱的设计开发过程中,如何准确分析行星轮轴承的载荷作用中心往往成为设计难点。根据当前风电齿轮箱的设计规范,在10MW负荷试验台上,对两台3MW风电齿轮箱进行背靠背测试,试验中对行星级齿轮进行了应变测试。以此次测试的输入级行星轮轴承为例,基于齿轮的应变测试结果,进一步挖掘应变测试数据的应用,使用最小二乘法原理,给出了确定行星轮轴承载荷作用中心的精确方法。

循环荷载下重载铁路道砟磨耗破碎及力学特性试验研究

为深入研究重载列车循环动载作用下散粒体道砟的颗粒磨耗破碎和力学行为劣化等特征,开展3种不同动应力幅值下的室内大型动三轴试验。通过对染色道砟颗粒进行激光扫描和三维重构,量化分析不同循环加载应力状态下不同粒径道砟颗粒的磨耗破碎特征,深入分析循环加载下试样的宏观力学特性和力学行为劣化等。研究结果表明,循环加载后道砟颗粒普遍从原始粒径破碎至相邻粒径,偶尔出现破碎至相隔粒径的现象,另有质量占比1%左右的少量道砟颗粒破碎至最小粒径4.75~22.4 mm;在相同的循环加载动应力幅值下,随粒径的增大,道砟颗粒破碎至相邻粒径的质量占比总体呈增大趋势;循环加载过程中颗粒磨耗存在尖角磨损、棱边磨耗与表面纹理改变等3种典型类型,动应力幅值230 kPa下颗粒最大磨耗深度为0.36~5.2 mm,平均磨耗深度为0.03~0.62 mm,颗粒磨耗程度随粒径的增大而逐渐加剧,尖角磨损出现的数量更多且概率更大,其次为棱边磨耗;循环加载三轴试验前后各粒组颗粒含量变化幅度与级配曲线偏移距离随动应力幅值的增大而增大,Bg、Br与BBI 3种颗粒破碎指标均随动应力幅值的增大而增大,Br与BBI两者对动应力幅值的变化反应程度一致,并且更为灵敏;试样轴向累积塑性应变、阻尼比与回弹模量均随动应力幅值的增大而增大。研究结果可为重载铁路散粒体有砟道床长期服役性能劣化评估及其养护维修提供理论依据和技术参考。

不同拔牙方式对骨性Ⅱ类错[牙合]畸形Bolton指数及咬合关系的影响

目的探讨不同的前磨牙拔除方式对骨性Ⅱ类错[牙合]畸形Bolton指数及咬合关系的影响。方法筛选62例符合研究标准的骨性Ⅱ类错[牙合]畸形患者的记存石膏模型,通过iTero Element扫描仪将石膏模型转换为数字化模型,每一例模型均按照常见的4种前磨牙拔除方式进行数字化拔牙,并进行拔牙后的排牙实验,计算拔牙前后的Bolton指数,并对排牙实验所建立的咬合关系进行评估,探索其变化规律。结果对于骨性Ⅱ类患者,四种前磨牙拔除方式均会导致Bolton指数全牙比明显减小,且相比于上4下4和上4下5的拔牙方式,上5下4和上5下5的方式会导致Bolton指数全牙比减小更多(P<0.001)。对于骨性Ⅱ类患者,在建立磨牙中性关系的基础上进行排牙实验,上4下4和上4下5的拔牙方式获得的前牙覆盖均值在正常值范围内(<3 mm);上5下4和上5下5的拔牙方式获得的前牙覆盖均值大于正常值(>3 mm),且差异具有显著统计学意义(P<0.001)。结论对于骨性Ⅱ类错[牙合]畸形的患者,上4下4和上4下5的拔牙方式更有利于使拔牙后Bolton指数全牙比趋于正常,也更有利于建立更良好的咬合关系。

基于锥形铣刀的渐开线齿轮两轴仿形倒角计算与加工

圆柱齿轮的加工毛刺与运输磕碰会对齿轮副的传动性能产生重要影响。对圆柱齿轮齿廓倒角加工技术进行研究,构建齿廓倒角加工的数学模型,基于仿真软件构建机床模型,编写加工程序完成齿廓倒角的仿真与分析。以此为基础,在铣齿机上完成了倒角加工实验,验证了齿廓倒角加工技术的可行性,为工业生产中渐开线齿轮齿廓倒角加工提供了新的解决方案。