Throughout MDSolids, the user is offered graphical or intuitive choices for all of the required data or units. In drawing shear force and bending moment diagrams, for example, the user can click on a picture of an arrow pointed down and enter the magnitude of the load to define a downward vertical point load rather than having to remember to enter a negative number for the load. In most cases, four common units (two US and two SI) are provided for each variable. For example, stress can be computed in psi, ksi, kPa, or MPa. The user is free to mix the units in any way desired. For example, a beam cross-section could be defined in millimeters, a beam length in inches, a moment diagram in kN-m, and the resulting bending stress could be shown in psi. All of these choices for forces and units are made by simply clicking the appropriate buttons on the displayed forms. The strength of materials concepts are difficult enough without adding confusion about software sign conventions and unit systems.

The software is written in Visual Basic to run in the Windows 95 environment. The software requires SVGA resolution (800 x 600). The software runs adequately on a 486-33MHz machine, but some of the graphics benefit from a faster machine.

• Segmented axial members
• A beam supported by two rods
• A two-bar assembly
• Hole Punch
• Bolted Connection
• Shear Key
• Bar and Pin
• Rod and Collar
• Bearing Stress
• Poisson's Ratio
• Stress-Strain Curves

1. For each problem type, the routine includes typical questions asked pertaining to the structure, common variations (such as double shear or single shear), and a picture or sketch that describes the problem geometry. After the student clicks the Compute button, the routine prepares a detailed explanation of the approach that should be taken to solve the problem using the user-supplied input data and units.

This module is devoted to a group of problems commonly used to introduce concepts of stress and strain. These problems feature a beam that is pinned at one end and supported by a rod, post, or strut at the other end. Often, these problem specify bolt or pin diameter sizes and either single or double shear configurations at the connections. The student may be required to determine the capacity of the structure considering limiting conditions on normal stresses in the strut and shear stresses in the connections. A beam and strut problem in any configuration can be solved by this module.

Statically determinate trusses can be analyzed for internal axial forces. Data input is visual and requires only the minimum definition from the user.

1. The overall dimensions of the truss are established by creating a user-defined grid of node points.
2. Truss members are defined by using a mouse to draw lines connecting the desired nodes. The software checks the members as they are defined to ensure that the truss idealization assumptions are satisfied (i.e., members connected only at the joints)
3. Supports and loads are also defined with mouse movements. The software checks to allow at least three support constraints and to accept loads only at the joints.
4. Labeling of joints is performed automatically. Angles of truss members are computed and displayed as the truss is created.
5. The analysis results are shown on the truss. Tension members, compression members, and zero force members are each indicated by a different color.
6. Optionally, normal stresses can be computed for the truss members, or given a stress limit, the required area for each member can be computed from the results of the truss analysis.

This module considers statically indeterminate axial structures comprised of two members. Problems of this type are usually stated in the following variations:

• Coaxial members
• End-to-end members with a load applied at the juncture of the two members
• End-to-end members with a gap between the two members and subjected to a temperature increase
• End-to-end members with a misfit between the two members that is closed before a load is applied to the structure (i.e., initial stress)
• Two axial members connected to a pinned rigid bar that rotates
• A bolt that passes through a sleeve with a nut that is tightened

Torsion of circular cross-sections is considered by the MDSolids software. Four different torsion member options are available. Notable features of these options are:

1. The user can define a simple torsion member (i.e., one shaft with one torque). This shaft is shown as a 3-dimensional representation. A grid is superimposed on the shaft to illustrate the twisting produced by a torque.
   
   
2. The drawing perspective is variable so that the user can look at the shaft from several viewpoints.
3. Optionally, an axial force can also be considered in the problem, and if the shaft is a pipe shape, the effects of pressure can be included. This permits problems with combined axial and torsion effects to be considered. Mohr's circle calculations can also be initiated from this torsion option.
4. Two torsion options consider power transmission problems. One of these options considers a single shaft connected to a motor while the second option considers a power shaft connected by gears to an idler shaft.
   
   
5. The power/idler shaft option also includes an animated motor and gear movement with simulated throttles so that users can observe the effects produced by changing motor power, speed, or gearing ratio.
6. Each of these three options feature a flexible problem definition format, similar to that used by TK Solver Plus. The user enters the known variables and the software solves for the remaining variables.
7. Extra explanations describe in words the specific procedure that should be used to solve each problem.
8. A fourth torsion option considers a single shaft with multiple torques. This option produces a torque diagram, a shear stress diagram, and a twist angle diagram.
   
   
9. Standard values for shear moduli are available to the user by simply clicking on the desired material.

Notable features of the statically determinate beam calculations include:

Notable features of the section properties calculations include:

1. Menus allow the user to calculate cross-sectional properties for 19 different generic shapes. General shapes include I-, T-, C-, L-, Z-, box, solid circle, pipe, and rectangular shapes. Double shapes include double I-, T, C-, and L-shapes.
2. Buttons on the display form allow the user to rotate the shape to the desired orientation. For example, a T-shape can be rotated so that the stem of the T points upward. This feature permits users to exactly match the orientation of the particular problem that is being solved.
3. The section properties calculated include the centroidal location, moment of inertia, section modulus, radius of gyration, plastic modulus, polar moment of inertia, and the maximum and minimum moments of inertia. The shape is redrawn to scale showing the centroidal axes.
4. The elastic modulus of the shape can be entered directly or the user can select from a list of common materials. For example, the user could simply click on "6061-T6 Aluminum" and the software will retrieve a value of 10,000,000 psi for the elastic modulus.
5. Section properties can also be computed for composite cross-sections. Two different materials can be selected and assigned to the desired portions of the cross-sections. For composite shapes, results are given in terms of the transformed area method for both possible transformations.
6. Dimensions and selected properties for the complete American Institute of Steel Construction listing of standard steel shapes in both US Customary and Metric designations is also included along with data on the various steel grades and the availability of specific shapes for each grade.
7. A tabular format is created for each shape analysis to give details on how to compute, for homogeneous shapes, (1) the centroids and moments of inertia, (2) the plastic neutral axis and plastic modulus, and (3) the product of inertia. For composite shapes, centroid and moment of inertia calculations are given converting material A into material B and vice versa.
8. The section properties calculations interact with both the beam and column routines. 

The column calculations are based on Euler buckling. Notable features of the column buckling calculations include:

1. Two elevation views (i.e., strong-axis buckling and weak-axis buckling) along with the corresponding cross-section views are shown for each column.
2. Any column end restraint (i.e., pinned, fixed, free, guided) can be selected for either column buckling direction.
3. The critical buckling load and stress is computed and the buckled shape is shown for the column buckling direction that controls.
4. The user can also add an intermediate support in either direction that can be positioned at any location between the two end restraints.
5. A plot of critical stress versus slenderness ratio is shown and the results of the two buckling directions are shown on the overall plot.
6. Optionally, the user may define the material yield stress and/or proportional limit so that the applicability of Euler buckling may be assessed.

Mohr's circle analysis for plane stress, plane strain, strain rosettes, and moments of inertia problems is available in MDSolids. Notable features include:

1. Normal stresses in the X- and Y-directions are specified in terms of either tension or compression stress rather than either a positive or a negative number. Shear stress is defined as either clockwise or counterclockwise on the X-face of the stress element.
2. An orientation diagram is displayed to show the stresses in the X- and Y-directions as specified by the user.
3. The Mohr's circle is drawn, labeling the points that correspond to the X- and Y-faces of the stress element. Separate pictures are drawn to indicate the orientation of the principal stresses relative to the XY coordinate system as well as the maximum shear stress orientation.
4. The drawings give users a clear visual depiction of the various angles in the X-Y space and the sigma-tau space as well as the directions of rotation in each coordinate system.
5. Stresses at any arbitrary orientation can also be investigated. A drawing surrounded with a protractor-like border enables the user to obtain stresses at any arbitrary orientation with merely one mouse click.
6. The Mohr's circle calculations can be accessed from both the beam and torsion member portions of MDSolids. Data from combined stress situations is automatically supplied from these routines to the Mohr's circle calculation.
7. Plane strain calculations can be made from normal and shear strain data.
8. Two types of strain gage rosettes (i.e., rectangular and delta) can be analyzed.
9. Principal moments of inertia can be computed from the moments of inertia about two orthogonal axes plus the product of inertia.