Standard Strength Test Research Articles

Braze microstructure evolution and mechanical properties of electron beam joined ceramics

A study was conducted to demonstrate the feasibility of ceramic joining using a high-energy (10 MeV) electron beam. Special emphasis was paid to define the beam operating parameters necessary to produce strong, hermetic seals. Electron beams with energies in this range penetrate through a significant thickness of ceramic (>1 cm), depositing their energy deep within a part. Thus, this process provides a special capability for producing joints at buried interfaces. Scanning electron microscopy (SEM) and an energy dispersive X-ray spectrometer (EDS) were used to evaluate the degree of reaction between buried braze metals and ceramic substrates. The mechanical integrity of cylinder joints was evaluated using a standard tensile strength test. The hermeticity of the joint was also tested. Specimens joined by electron beams were compared to specimens fabricated by conventional oven brazing. Prior to strength testing or sectioning for microstructural examination, some samples were examined non-destructively using ultrasound to evaluate the degree of bonding in the joint area. The microstructures of these ultrasonically identified ‘strongly’ and ‘weakly’ bonded regions were studied and compared. The sequence of phase formation at the ceramic-braze interface is explained in terms of changes in the chemical activity of titanium and microstructure in the solidified brazes. Mechanical strength and microstructural evolution appear to correlate well with the reaction kinetics involved at the ceramic-braze interface.

A Comparison of Functional Capabilities of Individuals With and Without Simulated Finger Disabilities: An Exploratory Study

Injuries to fingers remain the most pervasive nonfatal occupational injuries to the upper extremities in U.S. industries. It is logical to expect that work-related performance of individuals with finger disabilities (e.g., amputated fingers) will be inferior to those with all fingers intact and fully functional. However, the published literature does not provide any indication how much the functional capabilities of individuals with finger injuries differ from normal individuals. Knowledge of the nature and extent of decline in the functional capabilities of individuals with finger disabilities is necessary in order to make accommodations in the work place (including job, task, and equipment design), and meet ADA compliance. This laboratory investigation reports on the differences in the functional capabilities of individuals with and without simulated finger disabilities (amputations) when performing routine industrial tasks and standardized strength tests. Twelve male volunteers participated in the study. The finger disability simulated was of an extreme nature, and was defined as the loss of the use of four fingers in the preferred hand and the thumb in the nonpreferred hand. Subjects performed a variety of dexterity and strength exertion tasks. The dexterity tasks simulated finger dexterity in assembly work and manipulation of common hand tools and included: Modified Purdue Pegboard Test, O'Connor Tweezer Dexterity Test, Pennsylvania Bimanual Work Sample Test, and Hand-Tool Dexterity Test. The strength exertion tasks determined maximum volitional torque exertion capabilities when using common nonpowered hand tools, the psychophysical lifting strength, and standardized isometric arm, shoulder, back, and composite lifting strengths, and isokinetic lifting strength. Results indicated a significant reduction in performance for all dexterity tasks (p > 0.01). In comparison to normal individuals, the dexterity task performance times of individuals with finger disabilities increased by as much as 190%. The psychophysical lifting strength of the disabled was also significantly lower (<0.01), by as much as 35%. In contrast, reductions in standardized strength exertion capabilities of the disabled were smaller (between approximately 10% and 17%) and, for most tests, not significant (p ≥ 0.10). Strength exertion capabilities with hand tools reflected mixed results. While the torque capability of the disabled with both screwdrivers and wrenches went down, only the decline with screwdrivers was significant (p < 0.025). Overall, the results indicated that the performance of tasks that depended upon finger dexterity for completion, even those that required significant force exertions (e.g., psychophysical lifting strength exertion capability), declined significantly. While tasks that did not require appreciable dexterity and could be performed by the palm of the hand and thumb, or fingers, forming the two claws did not show a significant decline in capability. It is worth noting that the decline in capability in such cases, even though statistically insignificant, was very appreciable and of great practical consequence.

Experimental and analytical study of SIMCON tension members

The strength and ductility of slurry infiltrated mat concrete (SIMCON) tension members were investigated both experimentally and analytically to construct a mechanical model for simulating tensile force–displacement relationships. In addition to standard strength testing, special tests were conducted on tension specimens with preset cracks to determine the interaction between steel fibers and the cement matrix near an opening crack. These tests were conducted on two sets of preset-crack specimens: (i) with symmetrically inclined fibers and (ii) with aligned fibers having variable debonded lengths on each side of the crack. Using measured bridging forces of inclined fibers, an efficiency factor of plane random fibers, compared to aligned fibers, was determined to be approximately 0.58. It was found that the ductility of SIMCON mainly stems from plastic deformation of steel fibers rather than fiber pull-out. SIMCON tensile response was characterized by elastic, nonlinear hardening and softening regimes. The hardening response was notch insensitive without multiple crack formation. In the elastic regime, only minute stiffness reduction was observed. The nonlinear hardening regime was characterized by internal damage growth without visible crack formation and ended with the appearance of a co-linear set of partial cracks. The softening regime was described by a localized failure of fibers with variable failure strains at the co-linear cracks. Based upon the experimental observation that a co-linear set of partial cracks form at the ultimate composite stress, upper and lower bounds of the SIMCON stress–strain relation in the hardening regimes were obtained.

Interface Property and Apparent Strength of High-Strength Hydrophilic Fiber in Cement Matrix

This study addresses the characterization of fiber-matrix interfacial properties and the apparent strength of high-strength hydrophilic fibers. Single-fiber pullout bond tests and single-fiber pull-to-rupture strength tests were conducted by employing polyvinyl alcohol (PVA) fibers. The pullout bond tests showed that these fibers have surprisingly high chemical and frictional bond strengths. The chemical bond strength was relatively stable independent of a water-to-cement ratio of matrix and the fiber type tested, contrary to the friction bond strength. The pull-to-rupture strength tests revealed that the apparent strength of the PVA fibers in cementitious composites is considerably lower than that in standard fiber strength tests. The apparent strength was further reduced with inclining angle of fiber alignment. This effect was captured by a simple phenomenological model in this study, which introduces the apparent strength reduction factor. The combined effects of high bond strength and degraded fiber strength will likely contribute to composite performance less than would be expected from a high-performance fiber.

An Isoinertial Predictor for Maximal Acceptable Lifting Weights of Chinese Male Subjects

The practicality of using restrained as well as standard isoinertial strength tests in predicting the maximum acceptable weight of lift (MAWL) of Chinese male subjects was examined using a restrained strength test, which allows the subject to pull on the load in front of the body and to apply force in a functional free posture. Prediction models were constructed and evaluated under task conditions of two lifting ranges, two box sizes, and three lifting frequencies. The following measurements were taken for each subject in each test: (1) the body posture and joint angles, and (2) electromyographic activities of the arm muscles (biceps brachii), back muscles (erector spinae), and leg muscles (rectus femoris). Results indicate that the restrained knuckle height isoinertial strength (RK) was related significantly to the MAWL for all tasks, and the correlation coefficients ranged from 0.42 to 0.69. A step-wise multiple regression analysis based on data from the 22 subjects showed that RK, chest circumference, and thigh length accounted for 90 to 94% of the variance. A validation effort on a different sample (N=10) showed that the MAWLs can be predicted within an absolute mean (SD) error of 0.84 (3.30)kg. Percentages of muscle activation levels indicated that, other than strength from the erector spinae, the strongest contribution to the RK value was that of biceps brachii strength. Since the strength of the body's upper extremity was also recruited, the weak upper extremity strength of Chinese subjects was better reflected. Evidence for the existence of a close match between MAWL and RK values, and the conditions of the existence, suggest that RK is a good predictor for the MAWL.

The strength of auto‐cured and light‐cured materials. The shear punch test

This paper examines the versatility of the shear punch test as described by Roydhouse and suggests that it should be considered as an alternative to the present standard compressive strength test for glass ionomer cements and flexural strength for composite resins. The shear punch test can be used for examining small thin specimens, about 1.0 mm thick and 8.0 mm in diameter, of both auto-cured and light-cured restorative materials such as composite resins and glass ionomer cements. The preparation of the specimen is simple and does not require a precision mould or subsequent machining to size except that, after curing, it may need to be abraded gently to obtain flat parallel test surfaces. The test apparatus consists of a punch approximately 3.0 mm in diameter opposing a true fitting matching die. The specimen is supported over the die section and the punch is advanced through it in a compression cage. The formula used to calculate the shear strength allows for variation in specimen thickness and thus provides comparative data between materials. It also allows examination of the effects of variations in manipulation, maturation and storage of each material. It is suggested this test should be considered as an alternative to the present compression and flexural strength tests because it would provide a single strength test for a range of restorative materials being manipulated under a variety of circumstances. It is of particular significance for testing the light-cured materials because it examines a specimen size below that of the diameter of the exit window of a normal clinical light curing unit and also at a thickness where depth of cure of the material is not a problem.

Safety, health and hygiene in agriculture

Farming operations lack many of the constraints of factory work. Employees are isolated and work in very varied conditions with variable materials. In the past this has led to a poor accident record, but safety authorities have tackled the most severe problems through research, standardisation and legislation. This has produced a dramatic improvement in safety and health over the last 20 years. Tractor overturning used to be the main cause of fatalities. Analysis of accident behaviour, computer simulation and experiments have led to the development of standard strength tests for safety cabs and frames. An amount of energy, related to tractor mass, must be absorbed by the cab without deformation intruding into the operator space. These severe requirements have almost completely removed the risk of a cab collapsing, but drivers are occasionally thrown out and crushed. Research on stability should help to reduce the incidence of overturning. Ride vibration on tractors is consistently high enough to cause physiological damage. Suspension systems for cabs or wheels have been shown to overcome the problem but effective designs are only just beginning to be adopted commercially. Noise on tractors is difficult and expensive to suppress at source but insulation and isolation of the cab now provides acceptable levels for the driver. Other problems that have been improved through research include power transmission between tractor and implement, vehicle handling and braking, dust, heat and cold, workplace design and mental stress. Falls and falling objects are persistent causes of injury. In the future, robotics and autonomous vehicles may bring benefits in reducing the need for operators but generate potential safety problems.

Isometric Strength Tests: Predicting Performance in Physically Demanding Transport Tasks

A study explored the applicability of a battery of four isometric strength tests to steward, utility and warehouse jobs in a company that services offshore drilling and production facilities in the petroleum industry. The jobs involve frequently transporting materials up stairs, a category of tasks not prominent in situations where these tests have previously been applied. A job analysis established critical task requirements such as procedures, weights, distances, sizes of containers, etc. An experiment was then carried out with 25 male and 25 female subjects. The subjects performed two self-paced job-related tasks: transporting a 15.9 kg box up and down stairs and similarly transporting a 22.7 kg box. Measures included heart rate and amount of work performed, which, along with known task parameters, was used to calculate work power. Subjects also performed four standard isometric strength tests: grip, arm lift, back lift and arm press. Correlations between job task and strength performance indicated these tests are applicable to jobs with such requirements, thus extending the generalizability of the strength test battery.

Notch sensitivity of concrete and size effect Part I: Effect of specimen size and crack length by 3-point bending

The problem of notch sensitivity of concrete is discussed with the influence of size effect taken into account. The need to consider the size effect on the tensile strength of concrete was noted. It is shown that the critical stress intensity factor, K IC, is connected with the tensile strength of the material, which gives an opportunity to estimate the K IC-value on the results of standard strength tests of the unnotched specimens. In conclusion, a practical condition for quasi-brittle manner of failure has been found.

Low-cycle fatigue and cracking resistance of power plant boiler pipes and steam lines of 12Kh1MF steel

This paper examines the low-cycle fatigue and cracking-resistance characteristics of 12Kh1MF steel by testing specimens and full-size sections of steam lines produced from a single industrial batch of pipes with an external diameter of 194 mm and a wall thickness of 36-39 mm. The steel was also subjected to standard long-term strength tests and its chemical composition and mechanical properties were determined. The results of the investigation satisfied the technical requirements on the supply of steam lines and varied on the level of mean grade values.

Grafting starch xanthate with vinyl monomers and hydrogen peroxide in foam rubber production

AbstractStarch xanthate with degrees of substitution (D.S.) ranging from 0.12 to 0.56 reacted with vinyl monomers (acrolein, acrylamide, acrylic acid, acrylonitrile, methyl acrylate, or styrene) and hydrogen peroxide to form aqueous gels of starch–polyvinyl monomer graft copolymer. The same reactions conducted in a rubber latex medium resulted in a self‐acidifying, self‐heating, and self‐foaming coagulation to give a foam rubber. Such products were formed from several synthetic latices (NBR, SBR, polyisoprene, and polychloroprene types) and natural rubber latex; noted for each were the effects of the D.S., of monomer and peroxide concentrations, and of starch:elastomer ratios. The dried foams were evaluated by standard strength tests. Foam rubber of acceptable extensibility and enhanced tensile strength (up to 110 psi) was obtained with 0.12–0.15 D.S. xanthate and with proper balance of vinyl monomer, peroxide, and starch:elastomer ratio. Resilience was fair to good, but compression set was rather poor compared to most foam rubbers of general use.

An Indirect Tensile Test for Masonry Units

Abstract The failure of masonry in laboratory testing of walls and prisms and certain aspects of grouted construction is often the result of tensile splitting. These tensile stresses arise from differences in modulus of elasticity and Poisson's ratio between the masonry unit and mortar or grout. Since tensile splitting is so prevalent in masonry construction, a better means of evaluating the tensile strength of masonry units is needed. A splitting tensile test is proposed as a means of measuring tensile strength of masonry units. Splitting strength is compared to standard strength tests for 14 clay units and 14 concrete block units. Uniform failure modes and strengths support the adoption of a splitting test as a standard of masonry unit strength.

A computerized biomechanical model applied to analysis of skiing

Quantitative methods For the biomechanical analysis of sports activities are needed to guide teaching and safety practices and to evaluate the medical aspects of technique and equipment design. This paper describes a computerized model which was designed for the analysis of industrial tasks. The human body is treated as a series of seven links, enabling reactive forces and torques to be computed at each articulation. These can then be compared with maximum strength values determined by standardized strength tests in order to assess the likelihood of fatigue. The model may be usefully applied to the prediction of torques and forces in sporting activities as is illustrated here in a biomechanical analysis of downhill skiing. Methods are developed for determining heel lift force and gastroenemius tension. These tools are used to analyze two commonly taught downhill skiing positions, an erect basic running position and a crouched position, on different downhill slopes, and to compare these with the positions adopted by actual skiers. The model predicted that torques are greater relative to maximum strength at the ankle than at any other joint, especially in the erect position and in females. Ankle torques, heel lift force and gastrocnemius tendon preload may be reduced by adopting a crouched position, especially on steeper slopes. Fatigue inducing stresses are reduced by increasing the crouch and de-emphasizing the forward lean. Women should adopt modified body positions and have lighter heel binding settings. “Trade-offs” exist which refute the notion of a single “best” position.

Tensile strains in unreinforced concrete beams

Summary The behaviour of concretes and mortars subject to tensile strain was examined by measuring strains on the tension face of moist beam specimens during the standard flexural strength test. A wide range of concretes was examined with compressive strengths from 1,500 to more than 11,000 lb/in2 at 28 days. Initial cracking, as indicated by a significant deviation of the load-strain curve, was found to occur at tensile strains ranging from 41 to 158 × 10−6 for the range of concretes tested at 28 days. The corresponding average maximum tensile strains, measured before final crack propagation led to fracture, ranged from 75 to 240 × 10−6. These strains were affected by several factors but generally increased with increasing concrete strengths. The behaviour of mortars and concretes with high mortar content differed from that of normal concretes, and the tensile strains were much greater.

Study on the Strength of the Small Paper Bags

This paper discusses about the strength of two kinds of paper bags. One is a commercial packing bags made of bleached wrapping papers and the other, kraft paper bags. With the former, the results of falling test were compared with the Japanese standard strength test and special strength test.It was found that the _??_ type paper strengh, _??_ type paper strength and folding endurance have a good correlation factor to the results of falling test. (see fig 7-13, table 3) With the kraft paper bags, the rotation drum test and falling test by hand and by the instrument were experimented.It was found that the fluctuation of the rotation drum test is less than the fluctuation of the falling test by hand and by the instrument. (see table 5, 8, 9, 10).